A/C Upgrade Project starts tomorrow!

[mthomas58]

Holy crap was it hot today! Fine tuned A/C charge today. Evac'ed system, drained 1 oz oil from the compressor bringing my total oil charge to 6 oz and recharged 134a at 38oz using a 30lb container and scale vs 12 oz small cans . System was working great < 80 degrees, not great > 85 degrees. On max cool setting, I was getting some evap freezing and had to back temp setting down to avoid. As a result, > 85 degrees I was getting sustainable vent temps of about 43 to 48 degrees. Per discussions with Griff, I probably had some air in the system charging with 12 oz cans and I may have had a little too much oil in the system that may have saturated the evaporator and reduced heat transfer efficiency.

Temp above rear deck condenser (deck lid was down while charging)


Indoor temp in garage/ outdoor temp on top of the rear deck condenser


New charging set-up: 30 lb 134a container and scale.

[mthomas58]

Preliminary results are looking good after recharging with 38 oz using 30lb canister. Yesterday's commute home was 45 minutes in stop and go traffic at 98 degrees. Had temp set to max cold and fan at med speed. Vent temps held steady at 35 - 36 degrees and never cycled above 40 - 41. No evap freezing on max cold setting. Big improvement over prior charge.

[JFairman]

Hi Mark, could you mention what the low and high side pressures are in your AC system at 2000 rpm on a 88-90 degree day?
I have been through so much frustration with my new AC system and just can not get anything below 46 degrees out of my vents with the fan on high.

My car is an '87 930 and the system has a new Sanden 507 compressor, origonal 930 rear condensor with a high CFM 10" fan on the bottom of it pulling air through it during stop and go driving.
I have a rocker switch in the car mounted in the side of the auto heat box to turn off that fan when on the highway.
I'm using R134 from a 30 pound container, and I purge the yellow hose of air before charging and have the same new robinaire vacuum pump you have. I change the oil every other time I use it with the robinair "high vacuum" oil.
I've been doing 3-4 hour evacuations every time.

I also installed the narrow diameter barrier hoses, large aluminum serpentine front condensor, serpentine evaporator with new R134 expansion valve, and a procooler.
Also wrapped the evaporator box with closed cell aluminized thermal wrap and sealed the return ducts with foam rubber going to it.

If I check the system pressure when it's sat overnight and everything has equalized I'm at approx 95 psi when it's around 90 degrees out.

I've tried higher pressure charges and lower pressure charges and I can't get the vent temps any cooler than 46 degrees in 88 degree weather.

The place I bought all the stuff from has been very helpful and I can't complain because they have good honest customer service and they want to get to the bottom this too.

Anyway, I'm confused at what the R134a high and low pressures should be in 90 degree weather at 2000 rpm and you're having more success with this than me so any help is appreciated.

thanks in advance,
Jim

[mthomas58]

Originally Posted by JFairman

Hi Mark, could you mention what the low and high side pressures are in your AC system at 2000 rpm on a 88-90 degree day?
I have been through so much frustration with my new AC system and just can not get anything below 46 degrees out of my vents with the fan on high.

My car is an '87 930 and the system has a new Sanden 507 compressor, origonal 930 rear condensor with a high CFM 10" fan on the bottom of it pulling air through it during stop and go driving.
I have a rocker switch in the car mounted in the side of the auto heat box to turn off that fan when on the highway.
I'm using R134 from a 30 pound container, and I purge the yellow hose of air before charging and have the same new robinaire vacuum pump you have. I change the oil every other time I use it with the robinair "high vacuum" oil.
I've been doing 3-4 hour evacuations every time.

I also installed the narrow diameter barrier hoses, large aluminum serpentine front condensor, serpentine evaporator with new R134 expansion valve, and a procooler.
Also wrapped the evaporator box with closed cell aluminized thermal wrap and sealed the return ducts with foam rubber going to it.

If I check the system pressure when it's sat overnight and everything has equalized I'm at approx 95 psi when it's around 90 degrees out.

I've tried higher pressure charges and lower pressure charges and I can't get the vent temps any cooler than 46 degrees in 88 degree weather.

The place I bought all the stuff from has been very helpful and I can't complain because they have good honest customer service and they want to get to the bottom this too.

Anyway, I'm confused at what the R134a high and low pressures should be in 90 degree weather at 2000 rpm and you're having more success with this than me so any help is appreciated.

thanks in advance,
Jim

Jim, the ambient conditions you are describing mirror my orig attempt at charging. Per the attached P/T chart link

http://www.ackits.com/aacf/ptchart.cfm

My pressures came in at 20 and 235 but I believe I had some air and too much oil in the system.

On Sunday after recharging at 100-110 ambient my pressures were 30 and 270 to 280. At 38 oz of 134a, I'm right at 80% of the R-12 capacity (47.2 oz.) even though I have two addl condensers vs the stock set-up.

With a 930 you may want to think about adding an additional condenser to your system. I think condenser capacity is the real key to these systems at higher ambient temps.

I'd rely heavily on your component supplier as they should have some good empirical performance data on your setup to benchmark your results.

One thing for sure, there are lots of vairables to deal with!

Good luck!

[CatSkynr]

Originally Posted by JFairman

If I check the system pressure when it's sat overnight and everything has equalized I'm at approx 95 psi when it's around 90 degrees out.

I've tried higher pressure charges and lower pressure charges and I can't get the vent temps any cooler than 46 degrees in 88 degree weather.

The place I bought all the stuff from has been very helpful and I can't complain because they have good honest customer service and they want to get to the bottom this too.

Anyway, I'm confused at what the R134a high and low pressures should be in 90 degree weather at 2000 rpm and you're having more success with this than me so any help is appreciated.

thanks in advance,
Jim

A quick test you can run is to get a can of freeze spray. A can of air will work also, just spray it with the can upside down so you get the liquid coming out. With the AC running and your gauges connected, spray the bulb on the expansion valve. Your low-side should drop to almost zero. Now monitor your vent temp with your hand, it will happen fast. Do you feel a drop then rise in temperature? If so, this is where you need to look. Also, a tell-tale that your bulb pigtail could be the culprit will be lower than normal hi-side reading and higher than normal low-side readings.

Make sure the pigtail on your bulb is secure. I don’t use cork tape personally, I use silicone self adhesive tape (no sticky residue, good insulation properties and unaffected by temperature, doesn’t go soft or get hard). This keeps the pigtail snug on the lowside and is much cleaner IMO. Otherwise you want everything nice and clean (use brake cleaner, it will dissolve the cork-tape residue) and ziptie the pigtail snug on the lowside pipe before cork taping it. I have seen where the pigtail is actually on-top of cork tape, insulating it from the low-side pipe it needs to monitor temp from. Natural movement, bumps, improper install, messing with it, or whatever, it does happen.

Also, where did you get the expansion valve from? It may be needing adjustment.

As for charging 134A, rule of thumb I run is 30/250 at idle. I want to hit ONE of these numbers first, then I STOP. Next you walk it in slowly checking the temp difference at the center vent. I NEVER exceed 250 on the hi-side and you shouldn’t go beyond this or very far beyond it on a properly working AC. Remember, your low-side pressure represents your core temperature. So 32 PSI = 32deg F. (It’s not a perfect match nor ideal math, but that is the thinking behind it. Follow it and your job will be easier.)

[kuehl]

Originally Posted by CatSkynr

...... Also, a tell-tale that your bulb pigtail could be the culprit will be lower than normal hi-side reading and higher than normal low-side readings.

Not necessarily. More often this is a sign that compressor has a problem, such as reed valves or pistons and bores.

Also, where did you get the expansion valve from? It may be needing adjustment.

. The stock 911 expansion valves superheat setting typically works fine with R134a. Before you start messing around with what little room there is in the range of adjustment you would be better off measuring the superheat first.

As for charging 134A, rule of thumb I run is 30/250 at idle. I want to hit ONE of these numbers first, then I STOP. Next you walk it in slowly checking the temp difference at the center vent. I NEVER exceed 250 on the hi-side and you shouldn’t go beyond this or very far beyond it on a properly working AC. Remember, your low-side pressure represents your core temperature. So 32 PSI = 32deg F. (It’s not a perfect match nor ideal math, but that is the thinking behind it. Follow it and your job will be easier.)

No. The "rule of thumb" for R134a comes in two flavors:
A) 70-90% or 85% mean weighted value of the original R12 amount (ounces or grams), and
B) "R134a tends to run 10-15% higher in psi on the high side".
These industry "rule of thumbs" are generalizations. Your best method of charging is by P&T or Pressures and Temperatures. Your high side pressure compared to the ambient outside average temperature.
And the low side PSI is a "marker" of what your evaporator core temperature might be, other things that will affect the low side pressure are blockage in the system..... ice.

[JFairman]

"Your best method of charging is by P&T or Pressures and Temperatures. Your high side pressure compared to the ambient outside average temperature."

That must be good to know, but there's no explanation...

Would anyone be so kind as to say how the high side pressure should compare to ambient?
I remember someone saying the high side should be about 2.2X the ambient temperature. Is that correct?

I've been told to check the low and high side pressures at 2000rpm, not at my 800rpm idle. The low side pressure is a bit higher at idle than at 2000rpm.
Should I be going for a low side pressure of around 30psi at 800rpm or 2000rpm on a 90 degree day?

I can't go by the loss of weight in the 30LB bottle of R134 because I put in a thicker front serpentine condensor, a serpentine evaporator, and the high pressure barrier hoses are thinner than the origonal hoses.
I also don't have a scale for measuring it even if the sytem was unchanged from stock.

The expansion valve I have is set up for R134. I've tried 2 of them now and there was no difference. The curly end of the copper capillary tube from it is carefully hose clamped against the aluminum low side line and wrapped with tarred cork insulation tape.

Would the $500 serpentine rear condensor for a 930 from Griffiths, and the 10" puller fan I already have then mounted under it possibly make much difference in vent temps?

Thanks again for any help, in advance.
Jim

[mthomas58]

Originally Posted by JFairman

"Your best method of charging is by P&T or Pressures and Temperatures. Your high side pressure compared to the ambient outside average temperature."

That must be good to know, but there's no explanation...

Would anyone be so kind as to say how the high side pressure should compare to ambient?

Jim, the P/T chart that I linked gives you the acceptable range of High pressure temps for a given ambient while charging the system. Exceeding or being below the range would be indicative of an over or under charge (assuming there are no blockages or leaks......there I go with variables again)

[JFairman]

Thanks again but there are huge variables in that chart!
It's totally confusing to me.
According to the variables in that chart.. there are 2 seperate lines with 90 degrees in the spread which tells me that at 90 degrees ambient the low side could be anywhere from 25-39 psi.
Thats a really big make or break difference so maybe I'm just stupid but that chart just confuses me more.

I just want to know what the low and high side should be at 90 degrees ambient and then tell me what engine rpms that should be at... 800rpm or 2000rpm.


thanks again for trying to help.

[CatSkynr]

Originally Posted by JFairman

Thanks again but there are huge variables in that chart!
It's totally confusing to me.
According to the variables in that chart.. there are 2 seperate lines with 90 degrees in the spread which tells me that at 90 degrees ambient the low side could be anywhere from 25-39 psi.
Thats a really big make or break difference so maybe I'm just stupid but that chart just confuses me more.

I just want to know what the low and high side should be at 90 degrees ambient and then tell me what engine rpms that should be at... 800rpm or 2000rpm.


thanks again for trying to help.

Start with the low end of the spectrum at idle, check your vent temps. Run the engine to 1500rpm and verify pressure. I start at idle and verify at 1500, the second check. Work up not to exceed any of the hi end of the spectrum Idle or 1500. During the entire process, monitor your vent temp. Once you reach or get closest to the low end temp stated in your evap temp chart from your center vent, STOP. If you see your temp going up, STOP. Pay attention to what your pressures are and your center temp. That way if you go over and temp goes up, you can bleed off back to your known best.


Straight from the Federal Refrigeration License book from years ago.

Dealing with the hiside.

“if the refrigerant is behaving properly, the refrigerant gas will enter at a high temp, and the refrigerant liquid will exit at a lower temp. This is because it has transferred heat to the outside air. The difference is the temperature drop across the condenser which could be approximately 30F to 40F degree drop at idle or 40F to 60F degree drop at 1500 RPM, and the high pressure gauge reading will correspond to your value on the temp/press chart for the lowest temperature on the high side. Meaning the high pressure reading on a R134a system should be 212 PSI if the refrigerant is exiting the condenser at 135F degrees. If you don't have enough temperature drop across the condenser and high side pressure is too high, look at the possibility of an overcharge, air in the system, condenser, air flow and fans for a problem.”

Lowside

“if the refrigerant is behaving properly, at the evaporator the refrigerant liquid will enter and boil at a low temperature, approximately 35F degrees. There should be approximately a 10F to 20F degree difference between the evaporator outlet pipe and the line at the compressor suction port at idle, or 2F to 10F degree drop at 1500 RPM, and the low pressure gauge reading will correspond to a value on the temp/press chart, meaning the high pressure reading on and R134a system should be 30 PSI if the refrigerant is boiling in the evaporator at 35F degrees. If you don't have enough or any temperature drop from the evaporator outlet pipe to the line at the compressor suction port and the low pressure reading is high, look at the possibility of an overcharge. The correct charge will cause the line at the compressor suction port to be slightly warmer than the evaporator outlet, ensuring that liquid refrigerant will not be sucked back into the compressor. An overcharge will cause the system to not cool as well, pressures will be higher, and liquid refrigerant being sucked back into the compressor, shortening it's life. If you have very low pressure on the low side, the evaporator outlet pipe is much warmer than it should be, check for a low charge or restriction at the orifice tube or TX valve.”

::::added the chart for your reference to this:::::
http://home.earthlink.net/~bob1.gardner/sitebuildercontent/sitebuilderfiles/3refrigerantpressuretemp.pdf

[kuehl]

Originally Posted by JFairman

Thanks again but there are huge variables in that chart!
It's totally confusing to me.
According to the variables in that chart.. there are 2 seperate lines with 90 degrees in the spread which tells me that at 90 degrees ambient the low side could be anywhere from 25-39 psi.
Thats a really big make or break difference so maybe I'm just stupid but that chart just confuses me more.

I just want to know what the low and high side should be at 90 degrees ambient and then tell me what engine rpms that should be at... 800rpm or 2000rpm.
thanks again for trying to help.

The OFFICIAL 2000 RPM TEST published in the P shop manual (ref 800-10) reads something like this: at 77F, 2000 rpms, deck lid down, low side 12-30 psi, high side 115-205 psi. Now, why is this somewhat useless. Well you can see from the rather liberal ranges that it is a "double or nothing" standard, probably written by a conservative tech guru a P that most likely bet all his horses to show.
For example, if a you did have 77F ambient and your high side was only 115 psi chances are you don't have your gauge set connected to a stock factory air two condenser 911 using R12. If you do have your gauge set on a 911 then either you will find you are very low on refrigerant or your compressor is just about shot.
Looking at the low side suggested readings if this same stock factory ac 911 had low side of 12 psi chances are, again low refrigerant levels or problems starting after the receiver drier or expansion valve. Is there any benefit to the 2000 rpm test? Yes. But only if you know what the pressures and temperatures are at idle. That is the way most of the auto industry as well ac other ac industries gauge, calibrate and test ac systems.. generally at idle. Can you imagine your local HVAC tech coming out to your house to work on your refrigerator or home ac unit and saying to you "Ah. Fred. Could you crank up the voltage there for a moment, say from 115 vac to 175 vac, and ah, just hold it there for me. Will you?"
If you take your psi readings at idle chances are you will have a better idea as to whether everything is working properly. Then if you want to crank up the rpm's then be my guest. There are a few benefits, such as seeing whether you have clutch or belt slippage, maybe some obstructions in the system, maybe a noisey compressor. So, most the psi readings for establishing refrigerant capacity are done at idle. Now, you can find out whether you might be near peak or optimum charge capacity by checking the superheat however that is another subject.

With P&T charts, such as for R12 chart, if you were to look at a rather more detailed chart, such as in a MAC (Mobile Air Conditioning Society) training manual or maybe Snap-On's manual (I mention these because the are readily available), you might find specific ranges of ambient temperatures with a corresponding specific ranges of high side pressure. And I will digress for a moment here: When I (IMO) say "ambient" I mean the average temperature around the car. The reason I say "average" is because if you are testing on black asphalt compared to cement surfaces you are going to get higher ambients, or if the vehicle is between buildings or in an alley and there is a breeze you will find temperature swings or variations from the front of the car to back of the car. These differences can be enough to make you neurotic. So "we" say average ambient temperature. So these P&T charts have specific ambients with correlating high side psi's. If you look closely at them you will find that the correlation or factor is simply 2.4 This means that for a give ambient F temperature the suggested high side mean pressure should be 2.4 times the temperature, for example with R12 at 85F the
bogey in a perfect world to shoot for is 85F X 2.4 = 204 psi, and if you look at 100F you will find that 100F x 2.4 = 240 psi....... all of this in a "perfect world".

A perfect world means that for given ambient temperature the refrigerant pressure on the outlet of the compressor, in a system without any "air", must be xxx psi for the given type of refrigerant to work perfectly, with a perfect condenser system and perfect evaporator system..... and that leaves out the 911 stock factory system. Unfortunately some ac auto techs assume that with only 45 minutes of evacuation time the system is free of air and moisture. That may be possible with a front engine car with a front condenser and nearby evaporator system, however not true with the 911 which has typically 40 approximate feet of rubber hose plus two condensers and the evaporator. For systems like this "no air" is the rule!
This is where the P&T chart helps you to determine not only optimal charge (amount of refrigerant by pressures and temperatures) but whether you have an "air problem". With respect again to the low side pressure in the system, "if" you don't have any air or problems with residual moisture, then you might consider that 30 psi on the low side might reflect 32F in the evaporator core.

To find a better P&T working relationship with R134a there is a rather good "rule of thumb" stated by the manufacturers of R134a and the auto industry in general and that is "with R134a pressures tend to be 10% greater". However this rule of thumb is specific to an ambient temperature range. What I mean by specific range is that starting near 80F ambient R134a tends to run at a higher pressure than R12, and that difference is is more like an upward curve moving away from the R12 diagonal line. Once you start moving toward 95F ambients the curve shoots upward and the higher you go the straighter it climbs. So "we" have new factors or multipliers which we can safely apply to R134a or given "normal ranges of operation", say anywhere from 85F to 110F (desert people don't use refrigeration systems anyway, they use swap coolers). So this is how you estimate to a better finite target with R134a:
you recall the relationship with R12 was "2.4" (2.4 times the ambient should be the mean target for the high side pressure). The ranges for R134a "we" work with look something like this:

80-85F = ambient times 2.4 X 1.05 or the + 5% rule
86-90F = (ambient times 2.4) X 1.1 or the +10% rule
91-95F = ambient times 2.4 X 1.13 or the +13% rule
96-100F = ambient times 2.4 X 1.15 or the +15% rule
101-105 = ambient times 2.4 X 1.17 or the +17% rule
106-110 = ambient times 2.4 X 1.20 or the + 20% rule

Here is how you apply the rules:
Say you have charged the system with a known quantity of R134a refrigerant (grams or ounces or whatever) and the ambient temperature is 95F. Take 95 and multiply it by 2.4 = 228 psi and then multiply that by 1.13 = 258 psi. Now consider if you really had this pressure well that would be in a perfect world. Depending upon whether you parked on black asphalt or if the expansion valve was opening or closing this mean target of 258 might swing up to 270 or so and frankly that is pretty good in a 911 with R134a at 95F. Or, if you are testing with the deck lid down and your services hoses are holding the deck lid up an inch or two that would reduce the effective air flow across the deck lid condenser and drive pressures upward. Other things that can drive up the high side might be the sun beating down on the deck lid or maybe you just completed a few 0-120 mph test runs up and down your driveway (like I do).

And then you ponder your low side psi. Is it within a typical norm of 20-40 psi? : however knowing low sides usually move upward with the high side. The low side pressure does not mean a thing unless you have some vent temperature readings, and vent temperature readings, although low ones are your goal, don't really tell the true story unless you thermostat probe in the evaporator core and check the core temperatures.


So... to answer your question, at 90F what should you try to target on the high side using R12 the answer is 2.4 X 90 or 216 psi and with R134a it would 216 X 1.10 or 238 psi.... all in a perfectly KUEHL world..... at idle!

Reading Materials:
http://www.griffiths.com/porsche/ac/ice/index.html

[Mitch Leland]

Now that's impressive... A white paper from the King of Kuehl...

[mthomas58]

Originally Posted by Mitch Leland

Now that's impressive... A white paper from the King of Kuehl...

If you think thats impressive you ought to buy product from him and see what kind of support you get! Pretty rare these days

[JFairman]

Wow
That was excellent!
Thanks for all that, I hope it helps everyone as much as me.
Jim

[PSJoyce]

Thanks Griff! That's a huge help.

Paul

[Sunroof]

Best information I ever gathered.............thanks

Quick questions, please........

I plan on taking off my compressor to repair that high pressure hose fitting. It was an R12 set up and I have no idea if the AC guys at AutoKool here ever made a change in the oil in the compressor to R134 (what do I know?!). I have been reading about changing the oil, but am not sure of the procedure...........

Just what do you have to do with the compressor out.....................
Open a port and shake it out? Via gravity dump? Pressure purge? Vacuum suck?
Change any seals or gaskets? Are the R134 seals all "green"?
Top it off or leave some breathing room once empty when filling with R134 oil?

Should I take my compressor to be bench tested and have a shop change the oil?

Sorry for so many questions fellas, but this is why the Pelican board is such an awesome place to learn and share. I confess AC is not my best subject!

Thanks
Bob
73.5T

[mthomas58]

Originally Posted by Sunroof

Best information I ever gathered.............thanks

Quick questions, please........

I plan on taking off my compressor to repair that high pressure hose fitting. It was an R12 set up and I have no idea if the AC guys at AutoKool here ever made a change in the oil in the compressor to R134 (what do I know?!). I have been reading about changing the oil, but am not sure of the procedure...........

Just what do you have to do with the compressor out.....................
Open a port and shake it out? Via gravity dump? Pressure purge? Vacuum suck?
Change any seals or gaskets? Are the R134 seals all "green"?
Top it off or leave some breathing room once empty when filling with R134 oil?

Should I take my compressor to be bench tested and have a shop change the oil?

Sorry for so many questions fellas, but this is why the Pelican board is such an awesome place to learn and share. I confess AC is not my best subject!

Thanks
Bob
73.5T

What kid of compressor is it? If its a Nippo, remove the service H/L service port connections (on the bench) turn upside down to drain the oil and rotate the clutch using a socket wrench to cycle the pistons (forwards and backwards). Ester oil for 134a is compatable with mineral oil used with R12 so you should be ok.

More here:

http://www.autoacforum.com/messageview.cfm?catid=20&threadid=12050

[mthomas58]

Originally Posted by mthomas58

What kid of compressor is it? If its a Nipo, remove the service H/L service port connections (on the bench) turn upside down to draing the oil and rotate the clutch using a socket wrench to cycle the pistons (forwards and backwards). Ester oil for 134a is compatable with mineral oil used with R12 so you should be ok.

More here:

http://www.autoacforum.com/messageview.cfm?catid=20&threadid=12050

Some more related info from one of our resident experts - Jim Sims, copied from an old thread:

"Typically receiver/driers should be replaced whenever the system is opened for servicing. An old R/D designed for R-12 is not compatible with R-134a.

Cans of R-12 are not available "over the counter" to consumers. Do not mix R-12 and R-134a. When converting to R-134a the refrigerant oil must be changed. The system, if still holding pressure, should be taken to shop and any remaining R-12 extracted and recycled. Have them leak check the system. Then begin the conversion process:

Recommendations for good performance and value when converting a 911 from R-12 to R-134a:

- Extract any remaining R-12 refrigerant and recycle.
- Open all lines at low points and drain out mineral oil.
- Flush all condensers (this can be done on the car) and then allow them to fully dry out; again this is to remove the R-12 mineral oil.
- Do not flush the evaporator unless you remove it from the car and remove the expansion valve first. If the evaporator is out, clean the air side of dirt and lint and when reinstalling ensure the the foam air side seals are in good condition.
- Do not attempt to flush a compressor or a receiver/drier.
- Drain the compressor of mineral oil and replace with the appropriate amount of ester oil (POE). Use a fresh unopened bottle of ester oil; buy it in the 8 fluid ounce size bottles (NAPA and AutoZone sell this oil). If no other information is available regarding the amount of oil to add then replace what was drained from the compressor plus a ounce for every other component flushed or changed. For example, if two condensers were flushed and the receiver/drier replaced then add an additional three ounces over what was drained out of the compressor. Excess oil will impede performance as will R-12 system mineral oil left in the condensers.
- Install a new receiver/drier with XH-7 desiccant prior to evacuating the system. Most receiver/driers sold today contain the XH-7 desiccant. Inexpensive receiver/driers (less than $30) may be purchased from NAPA or AutoZone and can be used with some "hose flipping" if your wheel assemblies are not too big. Otherwise one will need the use the slender OEM Behr receiver/drier ($90+).
- Hoses if in good condition do not need to be changed to barrier style unless there is some other problem like a leaking fitting. If one is adding new fittings or components (such as a condenser or compressor) and can change both sides of the fitting convert to the o-ring style whenever possible.
- Replace all fitting o-rings using new HNBR rubber compound (usually colored a light green or blue) o-rings; coat the o-rings with Nylog (HFC compatible, part no. RT201B from Refigeration Technologies) gasket thread sealant and assembly lube. Also use Nylog on the metal to metal sealing surfaces of the flare type hose fittings.
- Install R-134a servicing fittings or adapters to both the high and low side; on some R-12 fittings it is necessary to remove the old Schraeder type valve core.
- Install a high pressure shutoff switch (wired into the compressor) in the high pressure line between the compressor and the first condenser. EPA requires that pro A/C shops do this when making the conversion to R-134a along with a sticker noting the conversion.
- Evacuate the system and leak check; if leak tight then evacuate for three hours using a good two-stage vacuum pump that can at least reach 40 microns of pressure; new dry vacuum pump oil in the pump is helpful as is having the car sit in the hot sun during evacuation.
- Charge the system using refrigeration pressure gages and thermometers) one at dash air vent closest to evaporator and one on the air inlet side of the main condenser) - the sight glass method doesn't work with R-134a. Air must be flowing over the condensers for proper charging - on a 911 have the engine deck lid down and the engine running at 2000 rpm. Do not over charge; converted systems will use less R-134a as compared to the original R-12 charge. Leak check the system at pressure.

If you do not understand these systems nor have the proper equipment seek experienced assistance and the right gear. A/C systems can blind, maim or kill you. Always wear eye protection.

A subcooler may be installed either before or after the receiver/drier in a 911. After the receiver/drier and as close to the evaporator as possible is better but not always feasible.

For improvements in performance I recommend (in order):
Proper conversion, charging and maintenance.
Better and leak tight air flow in dash and evaporator area.
Clean condensers with air moving over them (fans for slow traffic conditions- triplex pressure switched is the ideal).
Subcooler.
Better and more condensers.
Improved evaporators.

[Sunroof]

This is a fantastic site...........

Lots on upgrades, but I need some guidance on removing the evaporator, which I fee is the oldest component and in need of a cleaning. When I look into that smugglers box its intimidating!!

Removing hoses is straight forward, but how do you remove the evaporator? Are their any hidden connections (fan wiring, thermostat connection, drain hoses, etc) that are hidden and need special attention?

Is this a big undertaking? HELP

Thanks again

Bob
1973.5T Dealer installed AC

[Jim Sims]

"1973.5T Dealer installed AC"

Post a photograph of the evaporator/blower as installed (open the lid of the "smuggler's box" and capture an image of what is inside) - dealer installed can be several possibilities.