A/C compressor won't shut off

Check the pressure switches on the firewall I had one do that last summerr turned out to be the relay in the fuse box swap it with the horn relay to see if it fixes it

 

The thermal switch would be at the evaporator, but I don't recall your truck using one. It's possible that you have a bad expansion valve and being covered up by an overcharge of refrigerant.

 

I have never been able to replace just the clutch on a A/C compressor on a Peterbilt. Peterbilt always says it can not be done. There are other trucks that run a different compressor that you can do it on.

I had the same problem last year on mine and was told to replace breakers and sensors, never worked. The problem was the front seal on the compressor was leaking causing it to be low on freon but not low enough to shut it down completely. It would run for awhile then freeze up, thaw it out and it would do the same all over again.

Run a leak test on the front of the compressor and you should find your problem.

There are 2 small aluminum lines on the firewall and they both have a sensor in them. One is for high pressure and one for low pressure. These two sensor control the compressor and are what make the compressor cycle. So if you are low on freon the low sensor will cut the compressor out and when the freon comes back to it turn it back on.

 

Unplug the clutch and check and make sure there is a gap in the clutch (Air gap or back spacing). If there is no gap the clutch can not disengage even when it is not powered. If a shop did the work take it back, they may need to shim the clutch.

Best regards

 

The one on the condensor is for the engine fan the switch on the line next to the accumulater is the low aide switch and the other one on the firewall is the high side switch

 

Sounds like your under charged I usually set my low side around 25-30 psi and high side will be roughly 200 fan kicks on between 300-350 but this all depends on outside temp and altitude and I always charge the a/c with the engine fan on man