AC help! Running out of diagnostic ideas

[Cofferson]

Hey everyone. I am trying to work through an issue with the AC on my 2008 Silverado 2500 6.0 and need some help gathering info to get me there.

 

Problem: When AC is turned on in vehicle and temperature is turned to lowest setting, compressor will not engage.

 

What I've done:
- All fuses and relays good
- Verified pressures are good with manifold gauges
- Both pressure switches were replaced by previous owner. Jumped low pressure switch and still nothing. High pressure switch reading accurate per torque pro app.
- Verified clutch is capable of engaging by jumping relay. When i jump relay, air blows cold so compressor functions correctly and mechanical system is normal. Blend door is clearly operating. No ground at relay with AC on so the PCM isn't allowing compressor to turn turn on.
- No stored codes that would prevent AC operation.

- Tested the cabin air temp sensor and even jumped it to show the computer a high temperature.

- Ambient air temp sensor is reading accurate.

- I did a reset procedure I saw on here from awhile back of turning all HVAC off, disconnecting battery for 10 min, touching battery cables, reconnecting and starting vehicle, wait 5 min. No AC still.

 

At this point I'm convinced it has to be bad data from a sensor but I do not have all of the info to know which sensors will stop the computer from allowing AC operation. Previous owner (father in law) told me when it stopped working, the AC button would flash but this no longer happens.

 

Thanks in advance for any help.

[davester]

charm.li will have how the system operates and diagnostic procedures.