A/c Help Needed. Expansion Valve? Bad compressor?

[onedroppr]

Hi,

My car is a 1987 944 NA and this is my case. We are working on a tight budget. I removed air compressor to replace a worn pulley bearing. Main seal was also replaced, refilled with oil and installed back.

Because I got the car like 8 months ago, the compressor were never used. Just to test it, I threw in 2 cans of 134a without making vacuum; the compressor kicks on, verified the pressure and everything was working perfectly. Low side hose at the firewall was pretty cold and making nice condensation.

Next day on the morning, I take the car to my friends a/c shop to recover the refrigerant and make vacuum. Then after making vacuum I noticed system temperature where warmer and no was blowing nice cold air as when I test it the first time. Also low side hose at the firewall is no more making lots of condensation and to the touch is chill, but not cold. Also at idle air starts to feel warmer. At high speed, system seems to work good blowing cold air, but not as supposed.

So I put on the gauges and looked at the pressures.

With the system running:
Low side 40, so I assumed charge was good and no more gas is needed, pressure dropped significantly when car was accelerated, I understand compressor is making good suction.

Then high pressure was at 205-210, and keep rising to almost 230.

I know I didn't changed the dryer, but we were just testing the system on a pretty tight budget. What can be causing this problem. My tech says compressor seems to be working properly based on the pressure readings. I could be a stuck expansion valve problem? Any other idea that can help me resolve this problem?

Thanks and excuses for the long write, but it needs to be explained good.

[djnolan]

I am no expert, but the pressure sounds OK to me. The high side will creep up if the car is not moving.

Check your vent temps after driving the car for a few miles on the highway. R134a should get down to the low to mid 40's.

It won't get this cold at idle or in traffic, though, due to the inefficiency of 134a and the system being optimized for R12.

But if it gets down to the low to mid 40's while cruising that is an indication it is working correctly, and is probably as good as you will get.

Did you also make sure the system held a vacuum for 30 minutes or more? And you added two cans of R-134a, no more? You should add a little less 134a than what is called for for R12. Did you also add the proper amount of oil when you had the compressor open? Somewhere between 3-6 ounces is recommended.

[onedroppr]

Thanks djnolan for your response.

Yes, compressor was recharged with the correct amount of oil. The fact that make me curious is that before vacuum was done, i was sure temperatures where rounding mid 40's and the low side line at the firewall was pretty cold and sweaty. After the vacuum, vent temps rose to about mid 50's 60's and no more low side line being almost freeze to touch, now it's cool, never cold.

I got my doubts about the expansion valve being clogged when vacuum was done??

[onedroppr]

Reading at clark's garage I found some information about the pressures. I'm in the south part of Puerto Rico, with ambient temperatures rising up to 95-100F at midday, and I'm sure engine bay temperatures going over 150F easily.

So the recommended low pressure for an ambient temperature of 100F is 40-50psi, and the high side 200-250psi . I'm staying near low 40psi/ high 200psi to be safe with the system.

can I rise safely my car pressures to the recommended pressures given by clark's for my normal ambient temperature?

[aj951]

Those pressures and temps sound pretty normal to me with 134a. I use Freeze 12 (similar to 134A) and have the same type performance. I live in the south and the temps here in the summer run the same as you described above along with high humidity. It takes my system a while cruising at highway speeds to get the car cooled down, especially if it has been sitting outside in the hot sun. Once its get cooled down in the cabin, I switch on the air recirculate button.

AJ

[onedroppr]

The air recirculating button also works with vacuum?

[v2rocket_aka944]

Expansion valve clog would be more evident If the low side pressure were crazy high

[djnolan]

If the car is really warm, it is best to run with recirculate on and the windows open for a few minutes until the hot air has been. Leave the recirculate on and you are cooling air that has already been cooled, rather than sucking in hot humid air from outside. Also park the car so the dash is not in the sun or with a sunshade and it will cool down quicker.

[onedroppr]

Thanks! My main doubt is for the absence of condensation on the low side line going through the firewall onto the evaporator. Before vacuum system was cooling pretty good and almost frosting that line, now there's zero condensation on that line. Something had happen that prevent that.

[djnolan]

I feel your pain but the vent temp is the easiest way to see if the systems is performing . You need to have a dial thermometer to check the vent temps. Just put it in the center vent, turn on recirc and air and cruise to see what it cools down to.

I think they are under $10 at Autozone. OEM/1 in. dia. dial instant read pocket thermometer - Temperature Range -40 to 160 degrees Fahrenheit (24350) | Thermometer | AutoZone.com

[onedroppr]

Will do that tomorrow.

[onedroppr]

I take vent temperatures at afternoon at like 80-85F, 50% humidity: 60F at the vents.
At night vent temps remain the same, maybe 58F.

To reach that vent temps I made a 10 minute trip on the freeway cruising on 4th gear, more or less at 4k revs. During city cruising, vent temps were rounding 65, and getting warmer at red lights.

I'm sure before vacuum was made vent temps were close to 45-50F, and as I stated low side line was making a good amount of condensation, things that's not happening right now after vacuum.

Fans are working perfectly, and there's no chance of hot water at the heater because heater valve was bypassed.

Then a faulty drier can be causing this?

[djnolan]

It may improve with driving as the freon and the oil mix more. I think the proper system charge is 24 oz of R134a and 6 oz of Ester oil. Is there dye in the system so you can check for leaks? From your pressures above I would suspect the amount of freon was not correct, too little possibly. Or you have a leak and enough has been lost to affect performance.

There are several excellent threads on A/C system charging and conversion on this board.

Quick A/C filling question


BTW what year and model is your car?

[onedroppr]

1987 944 na.

[djnolan]

Good luck, let us know how it works out.

[mattdavis11]

Sounds like there is too much oil in the system and/or overcharged. Reduce to 80% of refrigerant charge from what it was with R12. Now that you have no idea how much oil is in the system, you may have to bleed some off. This is how you do it. Run the ac with the gauges on, place a rag over the charge hose (yellow) then open the high side valve. Watch the low, it should come down to about 35, high should be about 190.

Good luck.

[Bradical]

Expansion valve clog would be more evident If the low side pressure were crazy high

That is not true. A clog would cause lower than normal low side pressure. The more restriction, the higher the pressure drop entering the evaporator.

High suction pressures would be from high temperature load, refrigerant overcharge or a failed compressor.

[Bradical]

I take vent temperatures at afternoon at like 80-85F, 50% humidity: 60F at the vents.

At night vent temps remain the same, maybe 58F.



To reach that vent temps I made a 10 minute trip on the freeway cruising on 4th gear, more or less at 4k revs. During city cruising, vent temps were rounding 65, and getting warmer at red lights.



I'm sure before vacuum was made vent temps were close to 45-50F, and as I stated low side line was making a good amount of condensation, things that's not happening right now after vacuum.



Fans are working perfectly, and there's no chance of hot water at the heater because heater valve was bypassed.



Then a faulty drier can be causing this?

A clogged drier would result in lower than normal suction (low side pressures) and a low or normal high side pressure. One way to check for certain is to take a temperature reading entering and leaving the drier. If there is any temperature difference, then it is clogged.

I would check and ensure the condenser and evaporator coils are cleaned. Take a water hose and flush the condenser and radiator coils with just an opened end and make sure all of the sand and dirt is removed.