[bjedruszczak]

On 1994 S500, A/C just stopped working. It worked OK (not very cold) untill a few days ago.
I tried to charge it with R134a, but nothing goes into the system.
I noticed the compressor is not running. Sometimes it will turn for a few seconds when I first push the A/C button, and then it stops. Usually will not turn on again untill I shut off the engine and wait for a couple of hours.

I checked the refrigerant Hi / Lo pressure and it is about 70psi on both sides.
It seems like the compressor is being shut off because the pressure is too low. If so, How can I charge it if the compressor is not running.
Is there some kind of an reset button, or a way to force the compressor ON temporarily, so the system can be charged?
Any help appreciated.
Thanks,
BJ

 

[bluerooster]

On 1994 S500, A/C just stopped working. It worked OK (not very cold) untill a few days ago.
I tried to charge it with R134a, but nothing goes into the system.
I noticed the compressor is not running. Sometimes it will turn for a few seconds when I first push the A/C button, and then it stops. Usually will not turn on again untill I shut off the engine and wait for a couple of hours.

I checked the refrigerant Hi / Lo pressure and it is about 70psi on both sides.
It seems like the compressor is being shut off because the pressure is too low. If so, How can I charge it if the compressor is not running.
Is there some kind of an reset button, or a way to force the compressor ON temporarily, so the system can be charged?
Any help appreciated.
Thanks,
BJ

May be time for a new orifice tube. it has a screen in it that can get stopped up.
Also there may be a bad high pressure cutoff switch , leading the compressor to think it's running too high pressure, or the low pressure switch may be stuck, not letting the compressor know that it needs to engage.
with the compressor not running, both high and low will be the same. but 70 seems a little low, I would think it should be in the 100-150 range. When running it should be around 40 (give or take 10) and 250.

On most systems, (generic) the high pressure switch is located on the compressor, and the low pressure switch is located at or near the accumulator/dryer. usually, one can "short" the low pressure plug wit a paper clip, and force the compressor to run. but beware the pressures when you do this. Excessively high pressures and no cooling, means something is stopped up, probably orifice tube, or accumulator/dryer.
Remember, by no means am I an HVAC expert, but have experienced similar problems in the past, on other vehicles.