I have a 95 GMC Jimmy that has a minor issue I've never encountered before. The AC blows cold and works when turned on, but the compressor continues kicking on and off anytime the vent is on, such as running the heat or defrost. What might be causing this?

 

There are three possibilities:

1. The system is operating as intended. There is a low pressure cutoff switch on the accumulator that shuts the compressor off if the low side falls below around 35 psi. When the ambient temp (sensible heat)and/or humidity (latent heat) are high there is a high load on the system. The high and low side pressures are much higher especially at system start up (95F, 90%, hot cabin). As sensible heat, latent heat and/or cabin temp drops the load on the system drops and high and low side pressures begin to drop. In this lower load scenario the compressor can start cycling as the low side pressure bounces above and below 35 psi. This is normal.
2. There is a fault condition and the system is operating as intended to protect the system. There is also a high side cutoff switch if liquid line pressures become dangerous. Dirty condensor, pluged orifice tube, low refrigerant, failing compressor, etc. There is a fault that needs correction.
3. The system has failed and is not operating as intended. Bad voltages/grounds, failing controler, relay, wiring, compressor sensors, etc.

George

 

Thank you, any ideas where to start to figure out which one of those possibilities it is?

 

Buy an old school round stick vent thermometer and run the system on max cooling max fan. If the temp is around 40F while the compressor is cycling and you have good temp control then most likely your good. After that you need a good set of gauges.

George

 

Thermometer in the center vent.

George