u/JaguarEcstatic1247

Good evening GMT brotherhood.
2003 Yukon xl a/c compressor will not turn on. Test light shows no power to compressor wiring connecting with engine on, no power to low pressure switch on accumulator. When jumping a/c relay in fuse box compressor will engage.
This truck has the automatic hvac controls not manual.
What should be my next step, diagnosing controls/ module?
When a/c is commanded the snowflake icon illuminates.
Even when compressor is jumped and running, the hvac controls do not change temperature at all. Fully hot and fully cold feel hot. Rear a/c vents blowing much colder

Any help would be appreciated as I am a beginner at best mechanic and new to these trucks.