2007 GMC 2500HD SLT With Duramax Diesel

I work on industrial electronics and electric systems. So
I have some knowledge of electrical systems but I am not
that well versed in automotive electric/electronics
so I am asking you guys for your help.

When the A/C mode is set to Manual or Auto,
the air flow control is in Recirculate and
the status light is correct,
the compressor light in the comfort center is on,
the air from the registers is cold and flowing well,
and the vehicle is in motion. Everything is OK.

Problem is that with when the vehicle is stopped
for any reason, the A/C is still in Manual or Auto,
the air flow control is changing from Recirculate
to outside air and the status light is following it,
the compressor light in the comfort center is going on and off,
and the air from the registers is going from cold to hot and flowing well.
This is the problem.

To restate the problem.
When the vehicle is stopped.
The compressor will cycle on and off and
the air source will go from Recirculate to Outside Air
with out any change in the comfort center controls.
This behavior only appears when the vehicle is not moving.

Thanks in advance for all your assistance in this matter.
Thanks,
planttech

 

there may be a reprogramming update for the hvac module that addresses this. Check with the dealer for technical service bulletins.
This won't be warranty...expect to pay 1 hour labour rate for the reprogram.

 

Not sure about your year, but on the 09 I used at work, it's set up to start in RECIRC to get the inside air cold, then switch to FRESH after it reaches a certain temp. Mine had an AUTO position that controlled it. Might be working as designed. It seemed to happen mostly when in cold weather where the compressor ran to keep the windows from fogging. You could just have a low freon charge. You might also make sure the AC condenser fan is running when stopped.