A/C issues

PeteB

GT40s Supporter
When the car is cold, the A/C is working correctly with low side pressure around 40 psi and vent air is 45 degrees with 85 degrees ambient air. However, after the car has been running for a while, the low side pressure is going to high (~60 psi), causing the trinary switch to disconnect the compressor clutch. As soon as the compressor clutch disconnects, the pressure goes back down and turns the clutch back on. It then just constantly cycles and the vent temp is running 58-62 degrees. Any ideas on what the problem could be? :huh:
 
Your metering device is plugged i.e. orfice or expansion valve. Or you have moisture in the system that is freezing in the metering device or the moisture is turning into steam and expanding and causing ultra high pressures. Remove refrigerant and I would change the dryer and put on a vacuum pump get to at least 800 micron in vacuum. Change oil in your vacuum pump and let it run overnight to boil off any trapped moisture.
 

Allan

Supporter
Do you have the probe wire that goes into the evaporator core in place?
Did you try changing the setting on the ac temp knob?

The core may be freezing up.
 

PeteB

GT40s Supporter
Do you have the probe wire that goes into the evaporator core in place?
Did you try changing the setting on the ac temp knob?

The core may be freezing up.
I do have the probe wire in place. I tried adjusting the ac temp knob - no change.
 

PeteB

GT40s Supporter
Your metering device is plugged i.e. orfice or expansion valve. Or you have moisture in the system that is freezing in the metering device or the moisture is turning into steam and expanding and causing ultra high pressures. Remove refrigerant and I would change the dryer and put on a vacuum pump get to at least 800 micron in vacuum. Change oil in your vacuum pump and let it run overnight to boil off any trapped moisture.
Ok, I'll try that.
 
Is your radiator cooling fan running? Sounds to me like there is no heat being extracted from the condenser.......

Edit to add....that is the only thing that makes sense here unless you are grossly overcharged with refrigerant. The evaporator absorbs the heat from the air and the compressor compresses the refrigerant at the condenser to get rid of the heat.....the only way you can get high pressure on the high side is if you have a ton of heat build-up in the high side.....like no air flowing thru the condenser. High side pressure is directly linked to temp. It is impossible to have extremely high high-side pressure without having equally extremely high high-side temperature. If there is a restriction in the low side (plugged orifice or metering valve)....as my AC instructor in tech school used to tell us, "if she can't suck, she can't blow". In other words, if the orifice is plugged and nothing is getting thru, then the compressor has nothing to suck. If it has nothing to suck, it has no way to build pressure......just like if your PS pump has no PS fluid in it, it has no way to suck that fluid out of the reservoir to pump it and build pressure. Everything you describe here fits perfectly with no heat being extracted from the condenser. Once the entire system is "heat soaked" to max capacity (because none of the heat is being extracted from the condenser) it can't cool anymore and goes over-pressure.
 
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PeteB

GT40s Supporter
The cooling fans are running. It happens when driving at highway speeds also, so I'm not sure airflow is the issue.
 

PeteB

GT40s Supporter
Well, finally got a chance to call Vintage Air. Apparently their systems should only be charged to 10 psi on the low side. The shop that charged my system charged it to 30psi, so it was way overfilled.
 

Dan Carter

Supporter
Pete

Not an AC guy so if 10 is the low side what should high side read? I'm next on filling the system, I was watching your thread.

Thanks
 

PeteB

GT40s Supporter
Pete

Not an AC guy so if 10 is the low side what should high side read? I'm next on filling the system, I was watching your thread.

Thanks
The guy at Vintage Air said to only put two 12oz cans in the system. He didn't say what the normal high side is, but mine seems to stable out at about 180-200psi.
 
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