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 correctly.

griffiths

If you did not, you should also replace the 3 case o-rings and 4 manifold o-rings, as well as everything other o-ring in the system.

"If" the system was properly evacuated, there is no 'air' and no moisture,
and the compressor is pumping, and you have the near correct amount of refrigerant, you should see a reasonable spread between the low side pressure and the high side pressure as you noted. The high side pressure will vary more greatly than the low relative to what the outside air temperature is; your tech should be charging based on "pressures and temperatures" and he should know what the high side is based on the outside air temperature.

If your expansion valve was stuck closed you would see a lower low side pressure. Ice in the line at the drier will do the same thing.
The most common problems with a suspect expansion valve is not the valve but rather moisture in the valve (that's why we replace driers).

The rise in high side pressure you noted, although not drastic, could be quite a few things:
1) When the compressor shuts off the high side will start to drop, when the compressor turns on the high side rises.
2) A faulty condenser fan will cause pressures to rise.
3) A failed hot water heater valve could raise vent temps.

There is only one way to 'test' the system correctly and that is to start off fresh with new orings, the right amount and type of oil, a new drier. Then evacuate, charge and test. And you should document it all, this means noting the ambient outside air temp, the amount and type of oil, the amount of refrigerant and type used, the low side and high side pressures at idle, vent temps at idle as well a driving vent temps.

fred27

Hi onedroppr,
second the very good points griffiths has pointed out.
Best to replace the receiver drier and evacuate your system. (and check your heater valve is operating ok)
Your high and low side pressures are similar to what I get and my system is cold.
What temperatures are you getting at your vents?
Good luck with it.

onedroppr

Ok, first of all thanks to Griffiths and to fred27 for their replies.

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?

NoRush993/951

Everything I've read said to replace the drier if the system is opened. It's not an expensive part. Get the seal kit so you have all the o rings. Made it easy.
The new drier is slimmer than the original one, so you'll need to rig the holding clamp up a bit to secure it tight.

griffiths

onedrop, let's go back to basics, grab your service gauges:

1)At idle, windows up, ac on max cold, compressor clutch engaged, what is the low side and high pressures at idle, and what is the ambient air temp when you are noting this? What kind of refrigerant is in the system and how much is in there?

2) Same conditions as above, locate the expansion valve inlet and outlets (thin tubing is inlet, large tube is outlet), what are the temperatures of each side (cold, warm, hot), if either side is sweating, which one?

3) Same conditions as above, locate the drier, inlet is from the condenser, outlet is to the expansion valve, what are the temperatures of each side (cold, warm, hot)?