A/C compressor runs while heater is on?

CVILLA

MEMBER
2001 CHEVROLET SUBURBAN
V8
2WD
AUTOMATIC
170,000 MILES

My heater heats less even while the temperature control is on hotest. I noticed that the a/c compressor is cycling on. What could be causing this? I tried putting the defrost mode on, then back to heater because I know that the defrost mode sometimes forces the a/c compressor on. Any ideas for me to trobleshoot?

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

More than likely you have a humidity sensor issue. On this vehicle, there is not a dedicated sensor for humidity but it is calculated based on temp sensors and sun load sensor input. The module will turn the compressor on even when the heat is on just to control moisture.

So we need to do two things. First if you have a scan tool we need to check for codes. Hopefully we have a code pointing to one sensor.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

If we don't have any codes then we need a scan tool that can monitor the input of each of these sensors. Basically we are looking for a sensor that is not reading close to the others. This will cause the A/C to come on as it thinks there may be humidity based on an erratic temp sensor reading.

I attached the info below for each of these sensors.

Please run through all this info and let us know what you find with this. Thanks

Images (Click to make bigger)