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My AC burns me up --- Summary of fix

My AC went progressively warm over time... to the point of being useless (in Miami.) After spending $$s after $s with mechanics over the years---who I now realize knew shi* about 911 AC---paying others for mediocre AC results is over. Here's a condensed Summary from over 100 pages and 2,300 posts from the now closed "My AC Burns Me Up" threads 1 & 2. With Pelican ACbrainTrust input, this thread documents the DIY journey to diagnose what went wrong... and make it right.


Beginning & Ending Delta Snapshots

Here's where we started. Outside ambient & driving vent temps shown...




Here's where we arrived... 52 degree delta.*



* Delta = temp difference


AC Operation Nutshelled

Refrigerant is pumped by compressor through AC system in two states: 1) gas state is "low" pressure side and 2) liquid state is "high" pressure side. As liquid refrigerant passes through thermal expansion valve (TXV) it expands into a gas. This phase change from liquid to an evaporated gas creates a temperature drop making the evaporator cold. Air from cabin passes through "evap" where cabin heat is transferred into refrigerant inside evap. Gas refrigerant is sucked from evap back to compressor. Once pumped beyond compressor, refrigerant moves through condensers where heat energy in refrigerant is transferred to outside atmosphere and gas condenses into liquid. Receiver / drier (R/D) provides space for liquid to accumulate before it once again enters TXV to begin cycle anew. A drying agent (desiccant) is incorporated in R/D to trap moisture. This prevents water from entering expansion valve where it can turn to ice and freeze the system.

Correction: Swap # 2 and # 3 in profile reference.


Project Car Notes

AC's in '80 911 with '85 3.2 engine. Has stock front & rear lid condensers and Sanden compressor purchased new 13 years ago (in 2001.) Kuehl upgrades to system were made in '06 including: complete barrier hose kit, high efficiency serpentine evaporator, fender condenser with fan, 3 under dash vents, and receiver / drier. While your car & system may be different, AC operation, components and repairs are same in principle.

______________________

Beginning the Diagnosis

First inspection checks level of refrigerant / pressure currently in system. Manifold gauge is needed along with an understanding of how to attach & use it. Blue gauge = low pressure readings. Red = high pressure. "Static" pressure reading is with AC OFF. Based on 74 psi static reading, there's some refrigerant in system, but... a little low. Given this AC system having NOT been serviced in roughly seven years, this slightly low pressure is not considered abnormal.

Next, engine is run at idle and AC is turned ON. Thermostatic (climate control) knob is turned full clock-wise (CW). Compared to static reading, high side pressure has increased---compressor is successfully compressing high side of system into liquid. And, low side pressure is lower---compressor is successfully sucking gas from evaporator. This suggests compressor working as it should. Pressure reading = 175 high psi / 29 low psi. High side pressure should be around 220'ish at idle. So, high side is slightly low. Given low refrigerant level indicated by static reading, this is not a concern at this stage of diagnosis.




Evap Inspection

To visually inspect bottom of evap, passenger's foot rest is removed first. Then resistor that's fastened to bulkhead is removed... 4 screws. With resistor out, there's access to underside of evaporator (through hole where resistor was.) Pictures are taken of underside with pocket camera. CAUTION: avoid bending evap fins when entering this area. Below is bottom of evap. Clogged like this, evap will cool but only marginally... just as is happening. This evap needs to be removed and cleaned. Later, a look at why this clog occurred and how to prevent it.




Evaporator Removal

911 evaporator is located in forward trunk inside smugglers box. Before removing evap from plenum (evap box,) refrigerant needs to be removed (recovered) from AC system. NOTE: It's illegal in most if not all states to discharge refrigerant into atmosphere. Recovery systems can be purchased or an automotive AC resource can do it. After recovering refrigerant, top half of plenum is removed first. This top section houses AC's blower. To begin extraction, the cable feeding power to AC blower is disconnected at cable junction (near top of box.) Next, a thermostatic probe is stuck down vertically into plenum & evap near where plumbing enters plenum. That probe is pulled straight up and out of plenum. Then the tube the probe resides in is pulled up and out. (Tube may be buried under a black tar-like substance.) CAUTION: avoid kinking / crushing thermostatic probe line. Next, black tar'ish stuff on plenum and around plumbing is carefully removed. This material is both a seal for the gap between plumbing and plenum and an insulator for "pig tail" sensor (that's buried under a metal clip under the tar on lower pipe.) CAUTION: avoid kinking or cutting into thin copper lines in this area. Those lines are sensor lines.




If there are brackets securing top half of plenum to car, those are disconnected at plenum. Next, retainer clips that secure top and bottom of plenum to each other are removed. Best to slide these clips off sideways. Prying them off typically snaps the plastic tangs off the plenum halves---particularly true on older 911's where plastic is aged & brittle. These clips rust so sliding them off sideways is easier said than done. Because connection system for this plenum will be modified, clips are pried off with no worries. When plans call for removing bottom of plenum from smuggler's cavity as will be done here, there's no concern for retainer clips dropping down when pried off---they will easily be retrieved later. CAUTION: When not removing evap from plenum, best not to let these clips fall as it's difficult to retrieve them. Finally, air duct is disconnected from plenum.




Top of plenum lifts up & off easily now. CAUTION: If binding... STOP. Make inspection. Determine why binding, and correct. CAUTION: Avoid damage to evap fins. A thin rubber seal exists between the top and bottom halves of box. If this seal is holding together and remains in place, best to leave it be. With top of plenum (AC blower housing, also called cage) removed, top of high efficiency Kuehl serpentine evap is visible here.




Crud on blower and housing reduce efficiency. These parts will be cleaned later. For time being, they're set aside in secure place.




To remove evap from bottom half of plenum, high and low side plumbing is disconnected. CAUTION: Use both a turning wrench and stationary wrench on these connections. Using just one wrench creates uneven pressure which can damage parts. High pressure fitting is disconnected first (top plumbing connection.) O-ring is then removed and both open ends are plugged / capped immediately. High side plumbing is moved out of way and same disconnect procedure is done to low pressure fitting (lower plumbing connection.) NOTE: there is no pressure in system after refrigerant is removed... except perhaps for a very small burst that may occur when loosening fittings. Photo below is view of high and low side fittings looking from behind plumbing towards front of car.



Above, arrows show refrigerant flow direction. High pressure liquid (red) comes from R/D and enters TXV... is misted and so expands creating low pressure and temperature drop in evap. After exiting evap, low pressure gas (blue) departs and heads back to compressor through hose typically located below floorboard on outer edge of passenger's side of car.

Continued

__________________
Karl ~~~

Current: '80 Silver Targa w /'85 3.2
Prior: '77 Copper 924. '73 Black 914. '74 White Carrera. '79 Silver/Black/Anthracite 930s.

Last edited by Discseven; 11-21-2014 at 08:08 PM.. Reason: Clarity
Old 10-15-2014, 07:25 AM
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Old o-rings are saved to ensure correct size of replacements. After plugs / caps (in all ports here) are inspected for security and plumbing is out of way, evap is lifted up and out of plenum. (Plenum is box evaporator resides in.)




Another look at evap. Welded appearance of debris is due to evap having been flushed with coil cleaning solution before visual inspection of bottom was made. Flushing top down = waste of time & money here.




Evaporator Cleaning

Large debris is pealed off by hand.




Evap is soaked in pure bleach. CAUTION: Ensure plugs / caps are secure. Also, bleach will eat aluminum. No distractions once 10 - 12 minute soak is begun. Only fin section of evap is immersed.




Once removed from bleach, plugs / caps are again checked for security. Evap is immediately rinsed thoroughly with clean running water. In this case, with GF absent, evap is run through dish washer a few times. CAUTION: Evap is positioned in washing machine taking water jets and supports into consideration. Don't want evap's fins bent during wash.




After rinsing, visual inspection of all evap channels is made. All channels are clear. This evap will now perform in high efficiency mode as it was designed to. If channels are not entirely clean throughout, repeat cleaning process. (With work required to get to this point, makes no sense to reinstall even a slightly dirty evap.)




Diagnosing Compressor Condition Via Oil In Evap

Oil exists in AC systems to lubricate compressor. Too much oil and AC system will choke on it and not function well. Too little oil and compressor can starve for lubrication and die... the "black death." (For correct amount of oil for your system, best to contact Kuehl for details.) To make inspection, the plug from evap's bottom port is removed and coin-sized sample of oil is poured onto white paper. Additional sample is poured onto plastic wrap to preserve oil sample (if needed.) Inspecting oil in this manner works best when AC has been run just prior to removing evap as doing so suspends undesirable material in oil. This oil is clear & clean with no suspended metal particles---suggesting the compressor being in good operating condition. If your oil appears murky, grey'ish in color, or contains metal particles, take a picture (save sample) and contact Kuehl for further recommendation.



Oil notes for R134a refrigerant is in post #6.


Removing Bottom Half of Plenum

With evap removed, empty bottom half of plenum looks like this (below). Tangs used to secure top and bottom halves can been seen along perimeter---partly missing in this case. Will resolve missing tangs later.




If resistor duct is not already out, it needs to be removed from passenger's intake area before bottom of plenum will come out. Resistor duct is attached to bulkhead behind passenger's foot rest. There may be a sticky seal of some sort on inside of plenum connecting it to resistor duct (as duct protrudes slightly into plenum.) If so, remove seal. (NOTE: Resistor is already removed from passenger's side intake in photo above.) There may also be duct tape connecting driver's side intake duct to plenum. If so, remove tape. With disconnects made, plenum now lifts easily out of smugglers box. Condition of driver's side duct seal to plenum is immediately inspected. Below, this seal is inadequate---it's allowing warm air from smugglers box / front trunk into AC system. This will be corrected later to ensure only cabin air being recirculated through AC system.




Smuggler's box is seen below before and after cleaning (with soapy water.) CAUTION: Rinsing this area with water is done conservatively or water will spill over passenger duct hole and into cabin. Collection of wood chips indicates stock, wooden foot rest deterioration. 2 small drain holes for smuggler's cavity are pointed to. Larger hole to left of small drain hole is evap drain hole. Black hose running vertically is drain from fresh air handling box situated under dash board.



Continued
__________________
Karl ~~~

Current: '80 Silver Targa w /'85 3.2
Prior: '77 Copper 924. '73 Black 914. '74 White Carrera. '79 Silver/Black/Anthracite 930s.

Last edited by Discseven; 10-28-2014 at 05:15 AM.. Reason: Clarity
Old 10-15-2014, 07:39 AM
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One "trick" on removing the clips that hold the evaporator box together: Put a piece of string through the little holes on the spring. When they fly off, you can retrieve the clip.

It is a shame the other threads were polluted with crazy theories and pointless BS.

This thread will be a great place for future searchers for AC problems to find some real answers and see that a total beginner with AC repair can indeed learn and figure out what really works and what is a waste of time.

Thanks for all the work to make this summary and the excellent documentation of your process of fixing the system. Enjoy the cold air of your AC!
__________________
Glen
43 Year member of the Porsche Club of America
1985 911 Carrera; 2017 Macan
1986 El Camino with Fuel Injected 350 Crate Engine
My Motto: I will never be too old to have a happy childhood!

Last edited by GH85Carrera; 10-15-2014 at 07:54 AM..
Old 10-15-2014, 07:47 AM
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Blower Cleaning

To remove blower from its housing, the mounting plate is first separated from blower housing by disconnecting the 4 corner nuts & bolts. Wires to motor were disconnected from motor noting which wire goes where on motor. CAUTION: If reconnection of power & ground to motor is not right, blower will spin in wrong direction.




Set screw that retains blower to shaft is loosened. Loosening agent is sprayed on shaft & blower and allowed to soak a few hours. With careful prying, blower and shaft part company. Blower is placed in a ZipLock bag... soaked, shaken, and rotated in a solution of CLR for about 3 hours. When removed from bag, blower is brushed with soapy water and rinsed to remove remaining crud. While not restored to like-new condition, this blower will now work far more efficiently than before. Bead blasting would have been the way to bring this part back to like-new condition.




Blower and housing parts before & after cleaning. Thin seal between top and bottom of plenum can be seen drooping down from top of box in "before" photo.




Prior to installing blower back on motor, the shaft---where it enters motor (arrow below)---is lubricated with drop of oil on each side. Blower is then reinstalled on shaft making sure there's clearance between blower and mounting plate (so blower rotates without touching mounting plate.) Before mounting blower plate to top housing, a small bead of silicone is placed around the surface of the plate that will meet the housing. This seals the two parts and precludes vibration. CAUTION: Avoid over-tightening nut's & bolts that secure mounting plate to housing as this plastic crushes easily. Lock nuts are advised here. Result of over tightening these nuts & bolts is seen below... Bottom left corner is cracking. Top left corner is half departed. Bottom right corner is entirely gone. A screw replaces the "gone corner" nut & bolt.




New Retainer System for Plenum

The older a plenum is, the more prone to cracking it is. Inspection and repairs are made as needed. Regardless of whether tangs on each side exist or have been snapped off, now is the time to decide how to secure top and bottom halves together. If tangs remain, stainless wire wraps can be used in place of clips as seen below. Credit: Ronnie's.930 / Ron for input & photo here.




When tangs are mostly gone as is case with plenum on hand, pressure supplied by closed smuggler's hatch will be used to secure plenum halves. High compression foam will be placed atop plenum to fill void between top of blower housing and inside of smuggler's hatch. While plenum halve mating surfaces have a male & female config to keep halves from shifting once joined, teeth will be made & installed so there'll be no doubt about plenum halves staying in place. Teeth material is 3/4" strip aluminum. It's cut into short segments, then bent to appropriate angles for each side, then drilled and riveted into place. On short sides of top housing, double rivets keep teeth from turning. On long sides, only one rivet is needed as tooth is butt against ceiling and so will not turn once riveted.




Thin rubber seal between top and bottom halves is worn out here. It's removed and gutter is filled with silicone... then about 2/3rds of silicone is removed to retain the gutter. With teeth installed, very little pressure is now needed to keep top and bottom halves of plenum correctly aligned---even if car takes significant jolt.



Solution chosen to join halves of plenum depends on condition of plenum tangs and personal preference.


Reinstalling Plenum

Before placing plenum in smuggler's box, a thin cushion is placed at bottom of smuggler's box where plenum rests. This "rest area" is specifically in area of evap's drain hole. Foam insulated AC duct tape is placed here with an "X" cut into drain hole area of tape. Plenum's drain spout will plunge through this X-slit when installed. Area around driver-side air intake is provided thick foam seal that's tack-glued into place.




Plenum is now positioned and driver-side intake seal is inspected (when plenum is resting fully down in smuggler's box.) To complete driver's intake seal, metallic duct tape joins driver's duct to plenum. Next, before installing evap, thin cushioning material is placed in each corner of plenum for evap to rest on. Where a high efficiency serpentine evap exists, the corner where plumbing meets serpentine requires slightly more depth in box. A thinner pad is therefore used in this corner to accommodate deeper plumbing. CAUTION: Keep corner padding to minimum thickness as evap should sit as low as possible inside box to gain as much top clearance from AC blower as possible.




Looking from passenger floor level into bottom of plenum. Four holes that secure resistor duct to bulkhead are pointed to. Gap between passenger's bulkhead and plenum is closed off by resistor duct. Resistor is now installed and sealed to inside plenum with "AC black tar" (or similar sealer.)



Continued
__________________
Karl ~~~

Current: '80 Silver Targa w /'85 3.2
Prior: '77 Copper 924. '73 Black 914. '74 White Carrera. '79 Silver/Black/Anthracite 930s.

Last edited by Discseven; 10-29-2014 at 09:14 AM.. Reason: Clarity
Old 10-15-2014, 07:53 AM
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Gaps created by serpentine plumbing are sealed off on bottom side of evap with thin plastic sheets cut and positioned as highlighted below. These two seals keep air moving through the finned area of evap. With plastic sheet seals in place, evap is lowered into plenum and it's stability on new padding checked. Kuehl evap is excellent fit in stock plenum.




Before making high & low fitting reconnections at evap, fittings---with plugs remaining in place---are cleaned with a clean rag soaked with brake cleaner. New o-ring sizes are compared to old then lightly lubricated with same type of oil already in AC system... PAG in this case. Two wrenches (as described in disconnect procedure) are used to reinstall low pressure fitting first. Then same procedure for high side fitting. Nuts are secured tightly---not super tight as o-rings exist here to make the seal.




After connecting high and low plumbing, plenum top (the blower housing) is lowered into place. Electrical junction serving power to blower is connected. Ignition is turned ON (accessories only) and AC is turned on to check blower working & spinning in correct direction. With blower operation confirmed, tube for thermostatic probe is inserted into plenum & evap making sure it makes good contact with evap fins---should feel friction on tube when inserting. CAUTION: If tube is loose, probe's temperature sensing ability will be compromised, potentially resulting in evap freezing. Next, probe is inserted in tube. Area around plumbing and plenum is now sealed with AC black tar and pig tail clip is completely buried (insulated). In photo below, equalizing capillary runs from TXV... behind TXV... and makes connection at low pressure line. This is not "preferred path" for this capillary. Preferred path is from TXV... ahead of TXV... to connection at low side plumbing. In preferred position, this capillary is out the way of any work preformed on nearby steering and/or brake lines.




Area surrounding plenum and air duct to cabin is insulated with 3/4" thick, high compression foam. Together with smuggler's hatch, this foam applies the necessary pressure to secure plenum halves (when hatch is closed.)




Receiver / Drier Replacement

Given last servicing of this AC system being about 6 years ago, and with AC system now "open," it's time to replace receiver / drier (R/D.) CAUTION: Avoid using an R/D that is received in unsealed condition. REASON: Desiccant in unsealed R/D is likely not good. Am using Kuehl R/D that comes sealed along with new o-rings, adapters if needed, and plug to protect sight glass.




Located in driver's side front wheel well, R/D is strapped to car with 2 screw clamps. There are also 2 (high side) hoses to disconnect/reconnect to make R/D replacement. 90 degree fitting goes at top of R/D. Removing wheel makes job easier. When installing, new R/D is opened and attached immediately with new o-rings that are lightly lubricated with same AC oil type already in system. CAUTION: Avoid opening sealed R/D and not installing it immediately as this degrades internal desiccant. Before final clamping, sight glass is positioned so it's as visible as possible when looking into wheel well at it. Plug located in sight glass is left in place to protect glass from driving debris. Below: Hose at far right holds refrigerant coming from compressor > rear lid condenser > fender condenser and is going to front condenser. Hose feeding into side of R/D serves refrigerant from front condenser. Hose connected to top of R/D feeds refrigerant to TXV & evap.




When replacing AC components, R/D in this case, it's necessary to replenish AC system oil that the removed AC part takes with it. For a Kuehl R/D, 1 fl oz of AC oil (PAG in this case) will be added to feed hose when charging system.

Schrader Valve Replacement

Schrader valves exist in high and low pressure ports near compressor. While not leaking in this system, with the system open the choice is made to replace them given how inexpensive they are. Buying them with the tool to remove and install them is a good idea as the right tool makes this job easier. Both high and low port Schrader's are same size. Old ones screw out... new ones screw in. CAUTION: Schrader's have plastic seals so no need to screw these in super tight---tight will do. Open ports are plugged / capped / or covered when making the switch.




Why This Evap Clogged... and How to Prevent It

There are two air intakes leading to plenum... one behind passenger's foot rest, the other to right side of driver's pedal cluster. Stock foot rests for both these areas are made of wood. Depending on conditions in a 911, these wooden rests can & do deteriorate. In this case, water in the cabin caused both foot rests to deteriorate. Driver's side had been updated to plastic but broke (below) and was removed years ago. At same time, carpeting that covers it was removed. Removing these two parts = bad idea.




With no cover over pedal cluster, light-weight debris near cluster has relatively easy entry to driver-side intake duct seen below. Gas pedal linkage is foreground. Entire area is thoroughly vacuumed after this photo is taken.




Cabin air entering AC plenum from driver's side makes passage through car's center tunnel. At rear of center tunnel, there's a hole for the shifter linkage to pass through. A large rubber seal should exist at this pass-through. Seals should also be in place for other portals in this bulkhead. All serve to isolate tunnel from engine area. Large rubber seal exists in this case but is loose. ZipTie is used to secure it. All other seals are in place here.



Continued
__________________
Karl ~~~

Current: '80 Silver Targa w /'85 3.2
Prior: '77 Copper 924. '73 Black 914. '74 White Carrera. '79 Silver/Black/Anthracite 930s.

Last edited by Discseven; 10-29-2014 at 09:25 AM.. Reason: Clarity
Old 10-15-2014, 08:10 AM
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Pedal cluster back plate is repaired. A notch is cut that now allows clutch pedal full forward movement. Not the most attractive fiberglass job but patch is solid and not headed for beauty pageant. NOTE: With this area restored to stock config, and with more attention given to minimizing debris brought into floor area, one cause for this AC's demise is corrected. Essentially, pedal cluster plate with carpeting prevent debris from reaching evap.




Deterioration of wooden passenger's side foot rest is also to blame for AC's performance decline. Wood inside smuggler's box comes from this board with the only plausible explanation (credit: Will) being that resistor duct was not attached for some extended period of time. Long term water leaks from around windshield, water bypassing windshield glass & seal, water from Targa roof leaks... all caused a slow deterioration of bottom edge of this rest. Wood is replaced with plastic. (While water leaks are now inconsequential with wood removed, they're repaired to about 98%.)

New foot rest is cut from 1/4" plastic Starboard. With this installed, second cause of this AC's demise is corrected.




To Prevent Clogged Evap:
  • Wood foot rest and pedal cluster back plate updated to plastic
  • Added slot cut in plastic back plate to allow clutch pedal full travel --- prevents clutch from breaking back plate
  • Carpeting over back plate is positioned
  • Carpeting near intake areas are configured to provide open / easy air flow through the 2 air intake channels
  • Floor area maintenance is improved


Charging Equipment

Modified manifold gauge, digital scale, vacuum pump, PAG oil (in the case of this AC), 30 lb R134a refrigerant tank, heating pad (or hair drier), and thermometer are used to charge this AC system.

Manifold gauges run the gamut in price points depending on how sophisticated you want to get. The gauge being used here (shown below) is economical at just below $90.




Purposely modified with +$50, the manifold configuration below includes an additional 3' hose and 2 in-line ON/OFF ball valves. The added hose is connected where the cap was on the "T." This modification allows both vacuum pump and refrigerant tank to be connected to manifold simultaneously. With this configuration, there's no disconnection of parts once evacuation and charging process is begun. This benefits the evacuation and charge procedure by keeping air out. Shut off ball valves on vacuum and refrigerant feed lines allow pump and refrigerant tank to be easily isolated from rest of system as needed.




Digital scale provides accurate way to weigh installed refrigerant. Scale must take at least 40 lbs minimum weight (given approximate 35 lb total weight of refrigerant tank when full.) This scale is from Harbor Freight for under $40. Problem with this scale is it has automatic shut off if weight does not change within a short period of time. (I have yet to check if this feature is adjustable.)




30 lb tank of refrigerant (R134a) allows charging without having to make hose disconnects/reconnects as is required when using 12 oz cans (unless multiple hoses are provided for multiple 12 oz cans.) CAUTION: Disconnects once a system is being evacuated & charged can invite unwanted air & moisture into AC system. $120 non refillable tank.




Oil

There are 2 types of R134a oil.

Ester:
1) Can mix ester with residual R12 mineral oil
2) Should not mix ester and PAG
3) Ester can absorb moisture so avoid leaving oil exposed to atmosphere. Ester absorbs less moisture than PAG
4) Ester comes in various viscosity's (Griffiths has been using 100 weight for the past 20 years without any 'wear' issues)

PAG (polyalkylene gylcol):
1) Avoid mixing PAG with with residual R12 mineral oil
2) Should not mix PAG and ester.
3) PAG's can absorb moisture so avoid leaving oil exposed to atmosphere. PAG's absorb more moisture than ester
4) PAG's come in various viscosity's


AC Evacuation & Charging

Evacuation removes air & moisture from AC system via vacuuming, purging, and holding vacuum. The more thorough this procedure is performed, the better the resulting AC performance is. Vacuuming is done with a vacuum pump. Purging is done with either refrigerant and/or nitrogen. The evacuation formula used to achieve 32 dF in this project is proprietary to Kuehl / Griffiths Technology as made available to Kuehl customers like myself. Step-by-step installation and high performance evac & charging instructions are part of Kuehl AC solutions. Personally speaking, Charlie offers more comprehensive support than anyone I know of, i.e., I called him after having purchased my system upgrades from him 7+ years ago... he was still more than willing to help me out with my AC. More, he's the AC genius in this and every AC thread giving more of his time and expertise than seems possible.

Liquid Charging is seamless to evacuation process as preformed here. With entire system including all hoses up to tank valve under vacuum from evacuation, and with:
  • AC OFF
  • AC system proven to be absent leaks
  • low side coupling Schrader valve open
  • high side coupling Schrader valve open
  • low side manifold valve closed
  • high side manifold valve closed
  • vacuum pump line ball valve closed
  • vacuum pump off
  • refrigerant feed line ball valve closed
  • manifold positioned so that touching / turning manifold valves will not effect scale readings
  • refrigerant tank positioned upside down on scale
  • refrigerant tank valve... is now opened and short line between tank valve and closed ball valve is now charged with liquid. Remainder of manifold hose is dry. This is a "dry hose" charge.

    System is now liquid charged by:

  • zero'ing out scale
  • opening refrigerant hose ball valve
  • opening high side manifold valve
  • ... 25 "dry hose" ozs of R134a from a 30 lb tank is injected in system. "Dry hose" meaning there is no refrigerant in manifold system / hoses when tank weight is zero'd out on scale (except for short length from 30 lb. tank valve to refrigerant hose ball valve.)
  • with slightly warmed tank, charge takes 15-20 seconds. (Heat pad is used to warm tank slightly.) CAUTION: Too much heat applied to tank is invitation to potential BOOOOM.
  • 2/10's of an oz before target weight is achieved, high side manifold valve (situated in a position that does not effect scale readings) is closed... and weight dribbles up to target weight.
Current status:
  • refrigerant target weight resides in system including manifold hoses (so entire scale weight is not in car's AC system.)
  • both high and low side manifold valves are closed
  • both coupling valves remain open
  • pressure in AC system is now allowed time to equalize... meaning both high and low pressures shown on gauges are moving to the same PSI pressure reading. (High reading is decreasing and low is increasing.)
Once high & low pressure is equalized:
  • engine and AC are turned ON
  • thermostatic (climate control) knob is turned full clock-wise (CW)
  • engine lid is down (blue painters tape can be used to seal lid to car for increased airflow over condenser)
  • condenser fans front & rear are checked to ensure running
  • engine is let idle for a few minutes... then run at 2,000 rpm for a minute or two... then let idle for a minute...
  • readings are taken.
This final sequence & timing (after equalization) is not necessarily "the way" to do this. What's important is doing this procedure the same every time pressures & temp readings are taken. The purpose being to reduce variables during testing. A variety of charge weights were tested. The lowest pressures & vent temps achieved to date in this 3 condenser system are based on a 26 oz "dry hose" liquid charge.




Liquid & Gas

Liquid is one way to charge. Gas is another. Liquid followed by gas can also be done. When accomplished correctly, either way or combo can be successful. CAUTION: Liquid and gas are both charged differently. Not knowing how to correctly charge AC system can potentially ruin compressor.

Vent Temps & RPMs

V-temps are typically lower when driving than when taking initial idle readings. This is due to increased air flow over rear condenser(s) and higher compressor rpms. Knowing this, it's not necessary to check v-temps and/or pressures at rpm's above idle... unless you like to do so.

System Freezing

Operating an evap below 32 degrees for an extended period can plug evap due to condensation in evap freezing. The exception to this rule is in exceptionally dry areas due to the lack of moisture in the air. In consistently humid locales, goal for vent-temps is just above freezing---which means evap is operating at freezing threshold. Thermostaic probe & switch serve to turn compressor OFF to prevent evap freezing.

Condensate

Water condenses out of warm air when warm air meets a cooler surface. This occurs in plenum on evap. Condensate from evap drains from plenum through bottom of car. Checking the drain once in a while is a good idea to ensure it's not plugged. (Exposure time for photo below makes water appear to be flowing from drain when actually it's dripping.)



Continued

Last edited by Discseven; 11-21-2014 at 08:18 PM.. Reason: Clarity. Add Thermometer.
Old 10-15-2014, 08:25 AM
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My Errors Along the Way
  • Mechanics - 7 + years ago when I did my system upgrade to Kuehl products, I changed parts, then handed car over to my mechanic to evacuate & charge. Recognizing now that it requires specialized knowledge to maximize AC performance, handing car / AC off to a non AC expert was error.
  • Tank vs Cans - When charging, started out using 12 oz refrigerant cans. Should have gotten 30 lb tank right away as learning & testing required more refrigerant than expected.
  • Tool inspection - Failed to inspect entire manifold system upon purchase. Bad coupling existed and so return to retailer was needed.
  • Matching threads - Failed to bring manifold along when getting associated parts. Mismatched fittings & threads required return trip to retailer.
  • Forgetting tools - Left manifold gauge & hoses tucked in engine compartment overnight (to hold a vacuum.) Forgot... and drove off in the morning. Manifold hoses ruined from engine belts cutting into them. Dodged very large caliber bullet on this one as carnage to engine could have been severe. Replaced high & low manifold hoses.
  • Oil overfill - After removing and draining oil from compressor, filled compressor with 6 fl ozs of PAG oil --- the TOTAL amount for entire AC system. Dodged another large caliber bullet here in that this error was discovered BEFORE running engine / AC. Removed compressor and drained. Also siphoned low pressure line as oil had drained into that line. Took a few hours to correct this error. Because only 3.5 fl ozs was recovered, oil for new R/D and back flushed evap is NOT added back to system. Calculation: Allowing 1 fl oz for compressor, 1 for R/D and 1 - 2 for evap, the missing 2.5 fl ozs not recovered from the compressor error leaves the system with a suitable amount of oil (based on there being 6 fl ozs in system to start with.)
  • Flushing TXV - Back flushed evap with TXV on evap. TXV should NOT be flushed in any direction. New TXV is installed.
  • Mishandling Schrader valves - Due to number times this system was tested combined with mishandling the Schrader valves, Schraders were replaced twice. "Mishandling" in this case refers to turning manifold coupling knobs too far when opening Schrader valves. Doing so can bend these valves and cause them to leak as I experienced. With pressure in AC system, this can be avoided by watching manifold gauges when turning coupling knobs to open Schraders as gauge will show when Schrader valve is open. In absence of pressure in system, it's necessary to know how many turns is required of your coupling knob(s) to open your Schrader(s).
  • Vent noise - Failed to check centering position of AC blower when blower was first removed. It was later discovered to be off center. Together with loose motor, this combination resulted in subtle but annoying vibration noise coming from vents. Repair is covered in post #86, #90, and #93.
  • Pro advice - Failed initially to pay attention to Kuehl. BIG mistake.

Hopefully, you'll bypass errors I made.


Extras

Following work was done but is NOT considered to have had an effect on lowering vent temps.

Nothing Working - At one point during project, AC was turned on and nothing worked. Unusual since it had been working moments ago and no adjustments to anything were made. A light tap on the AC relay inside smugglers box is solution. That relay is known to stick. 25 amp relay is advised here by Kuehl. (Credit to Ron for solving this issue over the phone.)

No Cooling From AC - When first pressure readings were taken, somehow upon completing this process, system pressure was completely lost. At the time, loss of pressure was not realized. What signaled something being wrong was AC no longer cooling after completing pressure readings.

Diagnosis of zero cooling went like this: Thermostatic (climate control) switch is suspected and diagnosed first. Volt test says switch has power and is conducting through switch. Next, pressure switch is suspected and diagnosed. It's bypassed and compressor clutch engages with ignition ON (accessories only in order to NOT run compressor), AC on, and climate control knob turned full clock-wise. Clutch engaging means either PS is bad or there's a lack of pressure in the system (or too much pressure which is unlikely in this case.) A manifold gauge is attached to reveal... no pressure in system---so PS switch is functioning as it should by cutting off (protecting) compressor. With no AC cooling immediately following the first pressure readings and no pressure in system currently, conclusion is something happened after completing the first pressure readings. Exactly what occurred still remains a mystery. Below, wiring diagram shows how to test switches by bypassing them.




Hose Inspection - To rule out any issue with the system's barrier refrigerant hose being kinked or similar, entire 40' of hose is visually inspected along with front and rear fender condensers. Nothing unexpected is found. Below, 2 of several inspection perspectives.




Compressor Oil Inspection - Even though oil inspected from evap suggests compressor being in good condition, to remove any doubt... compressor is removed and its oil drained and viewed. Below, oil is being emptied from open high and low ports into cup with paper towel filter. Oil is clean & clear confirming this compressor's good condition. (When replacing compressor oil, error was made as is noted in the "Errors" section above.)




Back Flush Evap - With evap removed, and to be sure no buildup of oil within it might be effecting evap's efficiency... evap is back flushed with off-the-shelf pressurized solution shown below. CAUTION: Remove TXV BEFORE doing this. What came out was clean (again suggesting compressor in good operating condition.) Evap internals are immediately dried after flush... then capped and set aside. 1 - 2 fl ozs of AC system oil should be added to system when evap is replaced or flushed. (When back flushing here, error was made by leaving TXV attached to evap. This ERROR as noted in Error section above.)




Thermostatic (Climate Control) Switch - 7+ years ago, thermostatic (climate control) switch was replaced. The new one, being wider than old, did not fit into console. Solution back then was to turn climate control knob full clock-wise and tuck switch behind console. It has never been touched since until this project. With AC now cooling to just above 32 dF at vent, a correctly operating thermo switch is necessary to both modulate cabin air temps and prevent evap freezing. Having kept old switch (and recalling that I had changed it out years ago only to change it,) the old switch is tested... and works. While console's inner walls can be cut to accommodate a wider switch, having to do so was avoided by using the old, smaller switch. Below, two similar-purpose thermo switches are compared. And smaller switch positioned in console tray.




Thermostatic Tube & Probe Location - Due to number of times tube & probe have been in and out of this evap, the necessary tight fit between tube and evap is gone. So old tube is replaced with tighter aluminum version and it's positioned at evap's center. CAUTION: Thermo probe needs to be kept at least 1/2" above bottom of evap. Going too deep with probe places it in warmer air below evap rendering its temp sensing incorrect. When an evap is cooling efficiently as this one now is, improper placement of the thermo probe can result in evap freezing.




"Thanks!"

Participants in the two prior and now closed "My AC Burns Me Up" threads... without you guys & girl, this knowledge wouldn't be here, and I'd not be the "ice man" I am today. Credit due and my thanks to:

Kuehl - a.k.a., Godzilla / CG / Grif / Charlie
Ronnie's.930 - MONSTERON / Atilla / Ron
BobKontak - Honey Badger Narrator / Bob
JakeKooser - Jake
Stormcrow - Stormy / Steve
West - WW / Will
Crownarch - Cornstarch / Gary
DBCooper - DB
GH85Carrera - Glen
SilberURs6 - Eric
Ganun - George
Tirwin - Tim
DaveMcKenz - Dave
Pazuzu - Mike
Rick-I - Rick
Billybek - Bill
Hey April... you too
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Prior: '77 Copper 924. '73 Black 914. '74 White Carrera. '79 Silver/Black/Anthracite 930s.

Last edited by Discseven; 11-01-2014 at 08:53 AM.. Reason: Clarity. Add Schrader valve Error.
Old 10-15-2014, 08:35 AM
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Excellent post, thank you for detailing this.
Old 10-15-2014, 08:39 AM
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Quote:
Originally Posted by GH85Carrera View Post
One "trick" on removing the clips that hold the evaporator box together: Put a piece of string through the little holes on the spring. When they fly off, you can retrieve the clip.

It is a shame the other threads were polluted with crazy theories and pointless BS.

This thread will be a great place for future searchers for AC problems to find some real answers and see that a total beginner with AC repair can indeed learn and figure out what really works and what is a waste of time.

Thanks for all the work to make this summary and the excellent documentation of your process of fixing the system. Enjoy the cold air of your AC!
Hopefully people will read "rules" at beginning and understand the purpose. (EDIT: Rules have been deleted.)

TY for "thanks." Was a long haul project that turned out really well. Am pleased to load up Summary so others can benefit. I've gotten so much from forum... it's my way of giving back.
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Current: '80 Silver Targa w /'85 3.2
Prior: '77 Copper 924. '73 Black 914. '74 White Carrera. '79 Silver/Black/Anthracite 930s.

Last edited by Discseven; 11-21-2014 at 08:26 PM.. Reason: Rules deleted
Old 10-15-2014, 08:42 AM
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This would be a nice addition to the tech articles section.
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Old 10-15-2014, 09:27 AM
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Well, Karl, it sounds like you made it through. And just in time for Fall. LOL.

I read one thing I think you need to correct. It's about condensation. Water condenses out of warm air when that air meets a cooler surface. Why? Because warmer air has a higher capacity for water vapor, and colder air has a lower capacity. This is why in cold weather, the windows on your car will fog up. Warmer air inside the car meets a cold surface (your windows) and condensation occurs.

But overall, a damn nice write-up on how to (and how not to) make your 911 AC work well.
Old 10-15-2014, 09:29 AM
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Well done, well written, PP tech note?

Still confused about wood chips in bottom of smuggler's box, how did they get "there".

Also, I have seen posts, right or wrong, wherein the factory positioned T-stat is "calibrated" via changing the distance it is inserted into the evaporator core. Not to worry in your case with your placement the evaporator can never reach the factory low temperature.

Additionally, low Rh only means it will take longer for a sub-freezing evaporator to freeze up.
Old 10-15-2014, 10:03 AM
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Just a note..

Many years ago the "omega" spring, clutch pedal pressure helper, went "PING", lost somewhere out there, as I depressed the clutch. Was soon to learn that the clutch pedal "STOP" had functionality that I had not discerned when I repaired the pedal cluster. Allowing the pedal to over-travel will often break the spring or overstress it to the point that it "dismounts".
Old 10-15-2014, 10:14 AM
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Thank you very much Karl for a clear and concise write up. Now I will be able to see thru all the BS that got caught up in your project. Thanks!!
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Old 10-15-2014, 10:22 AM
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Quote:
Originally Posted by SilberUrS6 View Post
Well, Karl, it sounds like you made it through. And just in time for Fall. LOL.

I read one thing I think you need to correct. It's about condensation. Water condenses out of warm air when that air meets a cooler surface. Why? Because warmer air has a higher capacity for water vapor, and colder air has a lower capacity. This is why in cold weather, the windows on your car will fog up. Warmer air inside the car meets a cold surface (your windows) and condensation occurs.

But overall, a damn nice write-up on how to (and how not to) make your 911 AC work well.
Yeah... in the nick of time. Nice refinement on condensation. Will edit later today... TY Eric.
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Old 10-15-2014, 10:26 AM
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Quote:
Originally Posted by wwest View Post
Well done, well written, PP tech note?

Still confused about wood chips in bottom of smuggler's box, how did they get "there".

Also, I have seen posts, right or wrong, wherein the factory positioned T-stat is "calibrated" via changing the distance it is inserted into the evaporator core. Not to worry in your case with your placement the evaporator can never reach the factory low temperature.

Additionally, low Rh only means it will take longer for a sub-freezing evaporator to freeze up.
Kindling and loss of pressure after first test... still a mystery. Would be interesting to see someone figures out the wood in smugglers.
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Current: '80 Silver Targa w /'85 3.2
Prior: '77 Copper 924. '73 Black 914. '74 White Carrera. '79 Silver/Black/Anthracite 930s.

Last edited by Discseven; 10-15-2014 at 01:53 PM.. Reason: SP
Old 10-15-2014, 10:29 AM
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Quote:
Originally Posted by wwest View Post
Just a note..

Many years ago the "omega" spring, clutch pedal pressure helper, went "PING", lost somewhere out there, as I depressed the clutch. Was soon to learn that the clutch pedal "STOP" had functionality that I had not discerned when I repaired the pedal cluster. Allowing the pedal to over-travel will often break the spring or overstress it to the point that it "dismounts".
TY Will. Gonna have a look at that.
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Old 10-15-2014, 10:30 AM
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Originally Posted by NY65912 View Post
Thank you very much Karl for a clear and concise write up. Now I will be able to see thru all the BS that got caught up in your project. Thanks!!
Yaya... those threads got a wee off track on occasion. We'll see about keeping this one focused. My pleasure on Summary post Mike.
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Old 10-15-2014, 10:32 AM
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Quote:
Originally Posted by Discseven View Post
Kindling and loss of pressure after first test... still a mystery. Would be interesting to see someone figure out the wood in smugglers.
I'm "settled" that the loss of refrigerant was due to a 7 YO Schrader valve not seating. Were either of you aware, at the time, that over tightening the quick connect R-134a adapters could result in damage to the Schrader valve(s)?? Damage (internal, spring?) to a Schrader valve might prevent seating but still not be visible IMO.

Wood in bottom of smuggler's box almost had to be the result of operating the system with the passenger footwell inflow duct not in place for an extended period of time. You have had "possession" of the car for the entire ~8 year period?

Last edited by wwest; 10-15-2014 at 10:49 AM..
Old 10-15-2014, 10:41 AM
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Incredible writeup and summary. Saved for later and thank you!

Make sure you host your photos in a long term location.

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Old 10-15-2014, 11:45 AM
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