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troubleshooting AC compressor is this safe?

Lucky the Smiling Pirate

Lucky the Smiling Pirate

roadkill
Joined
Aug 4, 2005
Location
Phoenix, AZ, USA
so I'm pretty sure the AC compressor has been kicking on and off as recently has a month ago but it isn't now. None of the wiring leading to it appears to be damaged but in any case even a month ago when it was kicking on it took forever to get cold if it got cold at all.

This leads me to think that I'm low on refrigerant. The problem is that with the compressor not kicking on, I can't get an accurate pressure reading from the system and I'm worried I'll pop something if I overfill the thing.

I have one of those large cans with a gauge and filler attached to add some refrigerant and it says that if the compressor doesn't kick on to add half a can and then measure again. Is this safe? Right now, with the compressor off, the gauge reads something north of 150psi (the gauge goes to psi and the needle is pegged).
 
With the compressor off you should be reading 70 - 90 psi or less depending on ambient temperature. I would NOT try to charge into 150 psi static reading.
 
went and jumpered the compressor directly off the battery. it went and read about 18psi. I've filled it up to 30 now, though properly filled would need to be 45-50. Anyone know what pressure level it has to be at for the system to be willing to kick on the compressor automatically? When I plugged it back in, even at 30psi it wouldn't kick on on it's own.
 
Before you start adding refrigerant, get some proper gauges and hook to low & high side ports so you can read pressures on both sides of the system. Just because one gauges says your pressures are fine doesn't mean ****.

20 psi minimum with the compressor off, 50 psi maximum with the compressor on, give or take 2-3 psi.

If you're getting 150psi static you have other issues, it should read right around ambient temp.
 
well, it's a 92 740 so it's been 134retrofitted but not had the highside fitting converted.

It was about 1.4lbs low on refrigerant so it's back up to where it should be but the compressor still wont kick on. at the moment I have it wired directly to the battery through a switch so i can at least have some cold air while I figure out which point along the line is keeping the compressor from getting 12volts.

so far today I had the time to try jumpering the pressure switch on the dryer. that didn't kick things on. I got the air control module out and pulled off the metal panel that hides the pcb, but had to put things back together (left the panel off) before I could see if the solder joint to the relay is bad.
 
2.1lbs sound about right, sounds like you have a bad low side pressure switch. Compressor should kick on when you jump it.
 
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