A/C issues: Compressor will not turn off when switched off

[nightman61]

Good day everyone, checking my A/C system today while I am waiting on new windshield. Started car, let it run. I turned on A/C to check to see if compressor was working, seemed fine, just need a charge. I cut the switch off and noticed the compressor did not turn off with system turned off. I turned on defrost and moved temp up and noticed compressor turned off. When I bought this car, the control panel was in pieces. I replaced all of it. Is there another switch or relay to replace that maybe bad ? New switch on panel.

 

[Davea Lux]

Good day everyone, checking my A/C system today while I am waiting on new windshield. Started car, let it run. I turned on A/C to check to see if compressor was working, seemed fine, just need a charge. I cut the switch off and noticed the compressor did not turn off with system turned off. I turned on defrost and moved temp up and noticed compressor turned off. When I bought this car, the control panel was in pieces. I replaced all of it. Is there another switch or relay to replace that maybe bad ? New switch on panel.

On some models, the compressor will run with the defrost cycle to de-humidify the incoming air. If the system is discharged, the compressor should be off as the low pressure switch should disable the compressor circuit. You should not run the compressor if the system is low on gas as this will cycle the oil out of the compressor and burn it out. Have you replaced the vacuum switch in the control unit? A bad switch can cause the compressor to run all the time. You can disable the compressor manually by disconnecting the blue lead to the compressor clutch.

Dave

 

[Ripinator]

Good day everyone, checking my A/C system today while I am waiting on new windshield. Started car, let it run. I turned on A/C to check to see if compressor was working, seemed fine, just need a charge. I cut the switch off and noticed the compressor did not turn off with system turned off. I turned on defrost and moved temp up and noticed compressor turned off. When I bought this car, the control panel was in pieces. I replaced all of it. Is there another switch or relay to replace that maybe bad ? New switch on panel.

You didn't say what year, make and model your car is, but if it is a '73, your A/C compressor is behaving normally. To get it to turn off, move the temperature lever slightly to the right (warmer direction), and the compressor will turn off.

 

[bronze turbine]

The on/off control of the compressor is different for different years and models. It's more complicated than you'd think. There's a Chrysler Master Tech video on youtube that explains it.