I have a 2007 GMC Sierra SLT

The truck was a total waste. I decided to buy and fix it up. I have money into it and there are still a few blips.

Air conditioning is not working. Not blowing anything.

I have replaced the blower motor control module.

Blower works.

Replaced Pressure sensor.

Turns out the system will not hold 134a coolant.

Figured out that the system was leaking coolant from the radiator.
Replaced O-rings to the radiator.

The system cycles fastly when watching the pressure. Low side goes up to 90 then drop back down to 35 (or so). Then high side raises up to 125.
Over and over and over.

Was not sure, but replaced the Ambient Air Temperature Sensor.

On one of th HVAC Control Module I just forced it to blow ac and that's when I get the cycling.

On my other HVAC Control Module it says the ext temp is 55 so it never tries to start the ac.

I replaced the sensor in front of the truck for the ambient air temp.

I think the ext temp is the internal temp off the head liner. I will buy that tomorrow.

Can anyone suggest anything I've missed?

I have replaced or fixed anything that was wrong. Granted, I have the full service manual and the last on my list is PAG oil, but I do not know...

 

Expansion valve maybe. How many cans or ounces did you get in the system?