Expansion valve?
 

Has anyone experienced an open stuck AC expansion valve?

My AC holds charge, no leaks. The compressor runs continuously when required, but does not cool. No codes, the control valve solenoid gets correct current during the diagnostic run. The low side pressure is high and high side low.

So it's either the compressor or an expansion valve stuck open.

Thanks,

Tapani

Re: Expansion valve?
 

Those are the symptoms of an open expansion valve or a bad suction valve on the compressor. You can test it by running the engine at 1500 rpm and watching the gauges. Increase the rpm upward to about 2500 RPM. If
the low side pressure drops slightly, the expansion valve is
bad. If the low side pressure increases slightly, the problem is
in the compressor. Good luck!

Re: Expansion valve?
 

Ok, thanks for your response !

110 PSI engine not running, but hot. Ambient only 15C.... some kind of mixed juice in the R12 system. Was the same with R12 though.

High side 150 PSI, low side 54 PSI @ idle and 1500 rpm

High side 130 PSI, low side 60-65 PSI @ 2500 rpm.

Interestingly enough the low side never went down below 60 PSI again.

I will order a new compressor - do you know if the later compressor fits my 1992 for sure? I will charge with R134a. I know the expansion valve should be replaced with one with correct calibration, but it is quite a hassle... oh well.

Any thoughts?

Tapani

Re: Expansion valve?
 

i recently replaced a bad expansion valve on a 1970 super bee and when it came it was labeled r134a. since i intended to use r12 i contacted the manufacturer and they stated that since the opening rate was dictated by the temps and pressures it would operate properly. they said the only difference between the valves was the o-rings were meant for pag oil instead of ester oil. so you can probably use whatever you can find if you replace the o-rings. what kind of "mix" do you have? that freeze 12 stuff isn't supposed to be mixed with r12 that could be part of your problem. the newer compressor will fit.

Re: Expansion valve?
 

Well, the pressure of R134a is different from R12 at a given temp - so I've been told that the valves are calibrated differently. An R12 valve in an R134a system will hold the evaporator at a higher temp, so it won't cool as effectively. i was told that in an opposite situation the evaporator might freeze if the conditions are right. I swapped the valve in my Range Rover when the system was converted. This is all I know :-). The juice is supposed to be something to be used in a converted system. They are mixes of different stuff - the ingredients are the same as in R134a - only the %:ages are different. I forget the details. The symptoms were exactly the same with R12 - I just recharged it to check if it was low. Thanks, Tapani

Re: Expansion valve?
 

i was told the same thing in ac class in school about the valves. however the person i talked to at the manufacturer claimed it wouldn't matter because the different characteristics of the refrigerants would cause the valve to act differently. i would personally just continue to use r12 or change the valve if i converted but the guy did make a very technical argument.