Things already checked and determined working:
Refrigerant is neither too high or lowCompressor / clutch work as intended
fuse/diode/relay are good
Maybe ambient air temp sensor? Would like other thoughts before I go to local part store though.

 

Ambient air sensor doesn't have anything to do with the AC.
If the compressor is running and everything is right I got no idea.
Is the temp knob turned all the way red? Should be all the way blue.

 

Is the CEL lit?

Was the refrigerant checked with gauges and knowledge?

 

Knob is set to cool and on highAnd yes things were tested with knowledge (had a friend who's a professional mechanic take a look , he's stumped said occasionally he's seen ambient air sensors cause it but rare) relay was swapped with a known good one , no dice no cel (did have a code for thermostat which thought could be the reason for warm ac but nope)

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ill also add that it blows less "warm" (colder but not cold cold) when the temperature outside is colder
and it's not "hot" just generally "luke warm"
no cel did have a light for thermostat, but changed it and cleared the code

 

Quote : "Refrigerant is neither too high or lowCompressor / clutch work as intended"

What are the refrigerant pressure readings. Need to check both high and low side readings. Static pressure(compressor off) and AC on (compressor on ) should both be taken.
Has some work been done on the AC system that you didn't mention ? Your statement above about the refrigerant sounds like it has.

 

Are the blend doors operating correctly?

 

Are you aware that outside air comes in unless it is set to recirc?
If the mystery code is P0128 then it is the cause and the compressor is not running. What is the digital temp reading?
To explain: if the engine does not warm to 180F fast enough a code P0128 will be produced, this turns the AC compressor off. If the car is run then started again later on the engine will warm up faster and the AC will work. This condition is caused by not using the correct t-stat or the temp sensor is broken.

 

The thermostat should be an ACDelco 131-158, any other thermostat could be a problem.

 

And the coolant level could be low! Have you burped the coolant?

https://www.chevyhhr.net/forums/how-...-system-60614/