confusing AC gauge readings

[88911coupe]

Just completely replaced all hoses and added a rennaire evaporator (removed Procooler) in attempt to finally get ac going well. I took out the Procooler to simplify and some do well without it). Throughly flushed (used ac flush) original condensers and the new one added last year in wheel well. Nothing odd came out other than oil which was only faintly dirty, no particles of anything. Hooked all back up and, surprise, held vacuum for 14 hours. Ambient temps around 95 t0 100 here in Dallas. I added one can R134 using liquid charge into the high side with all off. Took most of can then shut all valves, started car and began to add 2nd 12 oz can. Trunk lid down with towels to keep air through spoiler vent. Temps getting cool inside car but not really COLD. Car ran several minutes then decided to check pressures and lower can into warm water to heat it up a bit. Lid down and I noticed low side about 25 to 30ish with high side fluctuating wildly and seemed high. I lifted lid and put RPMs up to 2k ballpark then high side settled down and was about 350 which seemed really high for less than two cans. Then...heart attack....connection into lid condenser let go and scared crap out of me. This is the 180 degree one which I was worried about crimping successfully. Yes, I know, get pressure switch. have ordered one but wanted to just see if ac was working generally.
So my question...are these pressures telling me something else is wrong? Sanden compressor that feels smooth as glass but a little noisy, not really sure what to compare it to. Not original but installed by PO so well over 15 years old. I don't know exact model but it has SD 7 on it IIRC.
Thanks

[wwest]

16-18 Oz fill..?

Repair the hose and charge, to "begin", with at least 36 Oz (considering the extra condenser)....

"Removed pro-cooler"... Good move, more of a detriment than otherwise.

At 95-100dF OAT canister pressure should be ~120 PSI, so you shouldn't need to heat the canister.

[wwest]

Originally Posted by 88911coupe

Just completely replaced all hoses and added a rennaire evaporator (removed Procooler) in attempt to finally get ac going well. I took out the Procooler to simplify and some do well without it). Throughly flushed (used ac flush) original condensers and the new one added last year in wheel well. Nothing odd came out other than oil which was only faintly dirty, no particles of anything. Hooked all back up and, surprise, held vacuum for 14 hours. Ambient temps around 95 t0 100 here in Dallas. I added one can R134 using liquid charge into the high side with all off. Took most of can then shut all valves, started car and began to add 2nd 12 oz can. Trunk lid down with towels to keep air through spoiler vent. Temps getting cool inside car but not really COLD. Car ran several minutes then decided to check pressures and lower can into warm water to heat it up a bit. Lid down and I noticed low side about 25 to 30ish with high side fluctuating wildly and seemed high.


I lifted lid and put RPMs up to 2k ballpark then high side settled down and was about 350 which seemed really high for less than two cans.

Lid remained up? The fender condenser's cooling fan working?

Then...heart attack....connection into lid condenser let go and scared crap out of me. This is the 180 degree one which I was worried about crimping successfully. Yes, I know, get pressure switch. have ordered one but wanted to just see if ac was working generally.
So my question...are these pressures telling me something else is wrong? Sanden compressor that feels smooth as glass but a little noisy, not really sure what to compare it to. Not original but installed by PO so well over 15 years old. I don't know exact model but it has SD 7 on it IIRC.
Thanks

[88911coupe]

I would "estimate" 20 ozs or so.

[kuehl]

Air in the system.

Ignore Wwest

[88911coupe]

Thanks, I had the vacuum on it for some time...maybe didn't get it all out. Thanks Griff. I was somewhat confused seeing those pressure with a "relatively" small r134 charge. I'll re do it and hopefully have better results.

[wwest]

Originally Posted by kuehl

Air in the system.

Ignore Wwest

When you revved up the engine the needle smoothed out, more compressor RPM will make up for low charge....

"listen" to Porsche, after all, they designed the system, not Charlie. Use the sight glass to charge the system, you can go back to Kuehl's method at any time if that doesn't prove satisfactory.

Use of the sight glass will assure that you get the right level of refrigerant, once you know that then you can record it. h.

Use of r134a might prove to be problematic had you not already added addition condensing capacity. Hopefully Zims, not adversely affected by the 500-800dF nearby (just inches away) IF heat source.

When you add the pressure switch please consider the Red Dot trinary, not only seriously extends the life of the fan(doesn't run if the engine fan suffices), but will help to keep the high pressure in the most optimal level for heat transfer.

Also, the Red Dot switch has a "safer" upper level compressor cut-out at 325 PSI, while many others go to 425dF or more.

[SilberUrS6]

Originally Posted by wwest

"listen" to Porsche, after all, they designed the system, not Charlie. Use the sight glass to charge the system, you can go back to Kuehl's method at any time if that doesn't prove satisfactory.

Hopefully Zims, not adversely affected by the 500-800dF nearby (just inches away) IF heat source.

Hey, instead of derailing this thread, why don't you start your own?

[SilberUrS6]

Originally Posted by 88911coupe

Thanks, I had the vacuum on it for some time...maybe didn't get it all out. Thanks Griff. I was somewhat confused seeing those pressure with a "relatively" small r134 charge. I'll re do it and hopefully have better results.

Listen to kuehl and ignore wwest. You'll get there. How long did you pull vacuum, and did you purge your gauge and fill lines of air, too?

[kuehl]

Originally Posted by 88911coupe

Thanks, I had the vacuum on it for some time...maybe didn't get it all out. Thanks Griff. I was somewhat confused seeing those pressure with a "relatively" small r134 charge. I'll re do it and hopefully have better results.

Pulling a 'vacuum' does not mean you have removed all of the ambient gases (air) from the system. Hence, pulling a vacuum and letting it sit for a day does nothing.

Telltale signs of an imperfect evacuation or lingering ambient gases (including water) in a system are:

A) High system pressures after only putting in part of the estimated refrigerant. Refrigerant does get along with ambient gases and drives up pressures.
B) Symptoms that mimic a closed TEV (water frozen inside the TEV due to a poor evacuation). I've seen more techs replace TEV's when there is nothing wrong with the TEV; the issue moisture freezing inside the TEV causing it to stick open, partially open or closed.

PS... Ignore Wwest

[88911coupe]

OK...as usual I learn a lot from Griff. Based on his last post it appears I did not completely evacuate the system. I truly believe he's fortgotten more than most of us know about AC systems. However, I'm confused about what i did wrong when vacuuming the system. I hooked up the high and low side then hooked up the common/central line to the vacuum pump and left it going for couple of hours. I closed the valves and let it sit...no loss then ran pump again. Is there a "dummies" version for this process somewhere on Pelican I can reference?

[Ronnie's.930]

Buck, here's what works for me to remove air/gasses from the system and keep outside air from re-entering during charging.



1) Manifold (gauges) hooked to service ports (high and low side) and vac pump (yellow hose).

2) Screw down manifold hose taps at compressor service ports to open Shrader valves (if your manifold taps have those type fittings).

3) Turn on vac pump.

4) Open manifold taps (both high and low side) and allow vac pump to run for 3 hours. If everything is hooked up right, and you have a vac pump that is strong enough, you will see the gauges bottom out very quickly (just a minute or so).

5) After three hours or so, close both manifold taps but leave the service port taps open, and observe the gauges - if no change in 30 minutes (vac holds), turn the vac pump back on, open the manifold taps, and allow the pump to work for one more hour or so.

6) Close manifold taps (leaving the service port taps in the open position), shut off vac pump, disconnect yellow hose from pump and attach to fitting on can or tank.

7) Open tap on can/tank (manifold taps still closed) and purge the refrigerant hose (yellow hose)of air by either using the purge valve on the manifold set (if it has one) - this is a Shrader valve that you push in with a small screwdriver, or the like, and refrigerant from the can/tank will shoot out pushing whatever air is in the hose with it - or lightly loosen the hose at the manifold connection until you hear refrigerant gas escaping. It doesn't take much refrigerant gas to purge the hose - just a couple of seconds worth.

8) Once the yellow hose is purged, open the low side manifold tap (can/tank tap still open) and allow refrigerant gas to enter the system statically (engine & compressor not running) for a minute or two. I have found that if the system is evacuated properly, that in about only a minute (with a 30 pound tank - don't know about cans) enough gas statically enters the system so that you do not have to bypass the pressure switch to get the compressor clutch to activate.

9) After initial static fill, start the engine, turn the thermostat and evaporator fan knobs to max, and check to see if the clutch has activated. I usually close the tap on the tank (leaving the others alone), start engine/compressor and then re-open the tank tap.

10) Observe vent temperatures and system pressures (car windows up and doors closed) and continue adding refrigerant gas until you are satisfied with everything or a problem shows up.

11) From time to time while charging, you will need to close the low side tap on the manifold (high side always closed during charging, BUTTofcourse) and observe pressures - they are different (at least the low side is) when the low side tap is open and refrigerant is entering the system than they are when the manifold taps are closed - you want to establish the closed tap pressures.

12) When satisfied with temps and pressures (with manifold taps closed), close the can/tank tap (if you haven't already), and turn the service port taps to the "closed" position and remove them from the service ports. If you want to avoid the "sort of" big hiss when you disconnect them, purge the excess gas trapped in the manifold and its hoses with the purge valve before you disconnect.

13) Check for refrigerant leaks. I use soapy water, that I dab on with a small paint brush, on every fitting I can get to.

Note - as a point of reference, and so I can brag some more , with my three condenser system (1 serpentine and 2, tube and fin) and serpentine evaporator, on a 95 degree day, I get high 20s vent temperatures with 30 low side and 220 high side pressures at the completion of charging. And no gauge needle fluctuations/flutterings what so ever.

PS - When wwest pipes up with some criticism, or doubt, of my method, or offers contrary advice and/or sight-glass malarkey (even though he has never done any kind of vac & charge procedure himself), weeellllll, you know exactly what to do!

[wwest]

Originally Posted by Ronnie's.930

Buck, here's what works for me to remove air/gasses from the system and keep outside air from re-entering during charging.



1) Manifold (gauges) hooked to service ports (high and low side) and vac pump (yellow hose).

2) Screw down manifold hose taps at compressor service ports to open Shrader valves (if your manifold taps have those type fittings).

A note of CAUTION: Some manifold r134a service port adapters have the ability to damage the Shrader valves if turned to far in.

3) Turn on vac pump.

4) Open manifold taps (both high and low side) and allow vac pump to run for 3 hours. If everything is hooked up right, and you have a vac pump that is strong enough, you will see the gauges bottom out very quickly (just a minute or so).

5) After three hours or so, close both manifold taps but leave the service port taps open, and observe the gauges - if no change in 30 minutes (vac holds), turn the vac pump back on, open the manifold taps, and allow the pump to work for one more hour or so.

6) Close manifold taps (leaving the service port taps in the open position), shut off vac pump, disconnect yellow hose from pump and attach to fitting on can or tank.

7) Open tap on can/tank (manifold taps still closed) and purge the refrigerant hose (yellow hose)of air by either using the purge valve on the manifold set (if it has one) - this is a Shrader valve that you push in with a small screwdriver, or the like, and refrigerant from the can/tank will shoot out pushing whatever air is in the hose with it - or lightly loosen the hose at the manifold connection until you hear refrigerant gas escaping. It doesn't take much refrigerant gas to purge the hose - just a couple of seconds worth.

8) Once the yellow hose is purged, open the low side manifold tap (can/tank tap still open) and allow refrigerant gas to enter the system statically (engine & compressor not running) for a minute or two. I have found that if the system is evacuated properly, that in about only a minute (with a 30 pound tank - don't know about cans) enough gas statically enters the system so that you do not have to bypass the pressure switch to get the compressor clutch to activate.

9) After initial static fill, start the engine, turn the thermostat and evaporator fan knobs to max, and check to see if the clutch has activated. I usually close the tap on the tank (leaving the others alone), start engine/compressor and then re-open the tank tap.

10) Observe vent temperatures and system pressures (car windows up and doors closed) and continue adding refrigerant gas until you are satisfied with everything or a problem shows up.

You need to define "satisfied with everything".

11) From time to time while charging, you will need to close the low side tap on the manifold (high side always closed during charging, BUTTofcourse) and observe pressures - they are different (at least the low side is) when the low side tap is open and refrigerant is entering the system than they are when the manifold taps are closed - you want to establish the closed tap pressures.

12) When satisfied with temps and pressures (with manifold taps closed), close the can/tank tap (if you haven't already), and turn the service port taps to the "closed" position and remove them from the service ports. If you want to avoid the "sort of" big hiss when you disconnect them, purge the excess gas trapped in the manifold and its hoses with the purge valve before you disconnect.

13) Check for refrigerant leaks. I use soapy water, that I dab on with a small paint brush, on every fitting I can get to.

Note - as a point of reference, and so I can brag some more , with my three condenser system (1 serpentine and 2, tube and fin) and serpentine evaporator, on a 95 degree day, I get high 20s vent temperatures with 30 low side and 220 high side pressures at the completion of charging. And no gauge needle fluctuations/flutterings what so ever.

11)...

An improved procedure would be to track the level of refrigerant charge in ounces and once you reach 75% of optimum level close the low side manifold valve enough to highly restrict the rate of refrigerant flow into the system.

That way the low side gauge will only show the suction side pressure and NOT the probable higher pressure of the supply tank.

Makes it less probable that you will overshoot the charge level.

[wwest]

Originally Posted by 88911coupe

OK...as usual I learn a lot from Griff. Based on his last post it appears I did not completely evacuate the system. I truly believe he's fortgotten more than most of us know about AC systems. However, I'm confused about what i did wrong when vacuuming the system. I hooked up the high and low side then hooked up the common/central line to the vacuum pump and left it going for couple of hours. I closed the valves and let it sit...no loss then ran pump again. Is there a "dummies" version for this process somewhere on Pelican I can reference?

It would help if you could more closely define "fluctuating wildly"..

Dither or jitter of the needle so fast as to only see the needle reversing at max and min readings?

Or so slow that the needle is visible throughout.

Actual range of jitter/dither or fluctuation...?

The kind of fluctuation that an intermittently slipping v-belt drive would cause?

And to "steal" from another post, did you purge the yellow hose of air each time you attached a canister?

And was the high pressure reading while the lid was open? And have you assured that the fender condenser fans runs?

[wwest]

According to the linked document a low charge such as you have would result in reduced "sub-cooling"(basically cooling of the refrigerant after it condenses into liquid) and thereby cause TXV "hunting".


Tips for preventing superheat hunting in TXVs

[88911coupe]

Thanks, to the best of my recollection I followed Ronnies process EXCEPT I allowed the R134 to flow in through the HIGH side. I thought I'd read that was ok but will let the refirigerant in from the low side next time. As far as the "flutter" it was very rapid and across a range of 50 to 75 pounds (rough guess from memory) It was so rapid the needle was practically a blur. Definitely not just moving back and forth from, say, a slipping belt.

[kuehl]

Originally Posted by 88911coupe

As far as the "flutter" it was very rapid and across a range of 50 to 75 pounds (rough guess from memory) It was so rapid the needle was practically a blur. Definitely not just moving back and forth from, say, a slipping belt.

Slipping belts are either a lose belt, compressor locking up, clutch slipping. Not common things to see. If you eliminate those, then its 'air' in the system related to inadequate evacuation. Damaged reed valve is not common. Read the Discseven threads, the gauge flutter was air.

Inadequate evacuation... use the 3M rule to solve.
Man,
Method,
Material.

Man... is not following correct procedures.
Method... incorrect procedure or misunderstanding.
Material.. components, gas, tools.

1) Test your tools. See if your pump can pull down as close to 30" as practical before you connect it to the system. This means fresh vacuum oil, good sealing points where service hoses connect to gauge set and ditto on service ports at compressor. A good compressor will pull a vacuum on the service hoses in seconds. Getting down to 30" can be impaired by your altitude. And remember that a gauge reading on an analog gauge is only as good as your: reading glasses, the width of the hash lines, the width of the needle, the accuracy of the gauge.
2) Insure your system is tight, new o-rings, barrier hoses, connections snug, not overtightened.
3) Since the system has over 40 linear feet of hose, plus condensers, evaporator, and drier, it is possible to initially pull a vacuum down to 30" and still have ambient gases or moisture in a system. AND... it is possible to pull a vacuum down to 30" or so and freeze trap the moisture inside a system before it 'boils off'. When you pull a vacuum know what the minimum vacuum level needed vs. ambient temperature to boil off the moisture.
4) Only use virgin R134a.
5) As noted, purge your service hoses before injecting gas.
6) Charge by 'gas', can upright, through suction side. You can charge by liquid however for DIY stick with gas procedure
7)Know how much refrigerant you are putting in, don't guess, document.
8) Document everything, system pressures, ambients, vents, etc.

Charging a stock system is a challenge for anyone. Charging a modified system is a challenge for a Pro. Doing it first time with out a hitch is like hitting the lottery.

[wwest]

Originally Posted by 88911coupe

Just completely replaced all hoses and added a rennaire evaporator (removed Procooler) in attempt to finally get ac going well. I took out the Procooler to simplify and some do well without it). Throughly flushed (used ac flush) original condensers and the new one added last year in wheel well. Nothing odd came out other than oil which was only faintly dirty, no particles of anything. Hooked all back up and, surprise, held vacuum for 14 hours. Ambient temps around 95 t0 100 here in Dallas.

I added one can R134 using liquid charge into the high side with all off.

The only potential problem would be if you didn't wait long enough for the liquid fill to vaporize before starting the compressor. Single can, 95-100dF OAT that would have happened quickly.

Took most of can then shut all valves, started car and began to add 2nd 12 oz can. Trunk lid down with towels to keep air through spoiler vent. Temps getting cool inside car but not really COLD. Car ran several minutes then decided to check pressures and lower can into warm water to heat it up a bit. Lid down and I noticed low side about 25 to 30ish with high side fluctuating wildly and seemed high. I lifted lid and put RPMs up to 2k ballpark then high side settled down and was about 350 which seemed really high for less than two cans. Then...heart attack....connection into lid condenser let go and scared crap out of me. This is the 180 degree one which I was worried about crimping successfully. Yes, I know, get pressure switch. have ordered one but wanted to just see if ac was working generally.
So my question...are these pressures telling me something else is wrong? Sanden compressor that feels smooth as glass but a little noisy, not really sure what to compare it to. Not original but installed by PO so well over 15 years old. I don't know exact model but it has SD 7 on it IIRC.
Thanks

What was the state of the system after fender condenser/fan was installed?

Was this the first fill after the new evaporator (and TXV?) was installed and pro-cooler was removed..?

PS: when trouble-shooting remotely the only dumb questions are the ones not asked...

[wwest]

14 hours of vacuum with OAT of 95-100dF any ice in the system would have evaporated away or been removed via sublimation.

A bit more concerned about "dirty" oil removed after only a year of operation.

"Charging a modified system is a challenge for a pro.."

Only if a certified A/C technician, "pro", or a DIY'er chooses not to use the factory recommended procedure.

[Pazuzu]

Originally Posted by wwest

14 hours of vacuum with OAT of 95-100dF any ice in the system would have evaporated away or been removed via sublimation.
.

??
Evaporated WHERE? Once he stopped pulling a vacuum and sealed the system, any moisture inside, iced or not, will remain...INSIDE. It won't evaporate away anywhere!

Want to remove ice? Pull a vacuum, then backfill with an inert gas to some pressure (maybe 30, 40psi?). Rinse, repeat. Backfilling with gas under pressure will keep the system clean, but allow that ice to melt and move around a bit. You need the mean free path of the water molecules to be long enough that they can actually fall into the pump, otherwise, they ain't going anywhere no matter how good the pump is or how long you pull vacuum. Deep vacuum systems don't work the way anyone thinks they do, and vacuum pumps do not "pull" stuff out of a system.


Hard chemical flush of system. This is doing most of the water removal.
Backfill with gas to check system under pressure (might leak under pressure even if it doesn't under vacuum)
Pump down for hours in high temp environment
Backfill with gas
Pump down for hours.
Maybe repeat again

THEN you might have a clean dry vacuum in your system. Also, adding heat at any point helps, you can activate molecules to jump off of the inner surfaces that they are stuck to with heat. That's the real problem, deep vacuum systems are essentially empty space and lots of crap sticking to the walls refusing to move. It doesn't matter how clean the empty space part is if you have lots of crap stuck to the walls.





Hey OP, how long did your system remain exposed to air? Is there a chance that your new dryer might be charged with moisture, and loading your system with water even after you pump it down?