A/C not cooling, compressor cycling

[Jeffrey Howell]

Hello all,
I am having an issue with my A/C. The compressor is short cycling and blowing hot air all the time. I tried changing the low pressure sensor on the canister and it didn't change anything. I added freon and checked the pressure but nothing changes and it still short cycles. The rear A/C has been blocked off with a block off kit. Any suggestions? It is a 2008 GMC Yukon SLT with the 5.3 V8 Flex Fuel and 154,000 miles on it. I just had the engine rebuilt and cammed it. it also has long tube headers and a cat delete if that makes any difference.
Thanks!!

 

[exp500]

Overserviced?

 

[Geotrash]

Hello all,
I am having an issue with my A/C. The compressor is short cycling and blowing hot air all the time. I tried changing the low pressure sensor on the canister and it didn't change anything. I added freon and checked the pressure but nothing changes and it still short cycles. The rear A/C has been blocked off with a block off kit. Any suggestions? It is a 2008 GMC Yukon SLT with the 5.3 V8 Flex Fuel and 154,000 miles on it. I just had the engine rebuilt and cammed it. it also has long tube headers and a cat delete if that makes any difference.
Thanks!!

Does yours have automatic or manual temperature control? Is the LED by the A/C button on the dash flashing when you try to engage it? Side note: if you discharged the system when you replaced the cycle switch, it needs to be recharged by weight after drawing a vacuum on the system for 45-60 minutes to dry it out.

Here's a couple of schematics for the system. Since you already replaced the pressure sensor, I would be inclined to suspect that either the compressor relay isn't staying closed or one of the temperature sensors has failed. If you have access to a Tech 2 scanner or equivalent, you can do a better diagnosis for what's happening. For example, you can see if the evap sensor reading is within spec. Couple easy things to try if you don't have one: clean the grounds in the circuit, and swap the relay with another one.

Schematic for the compressor controls:



And here's one for the front temperature sensors:


And the diagnostic procedure:

 

[Jeffrey Howell]

Does yours have automatic or manual temperature control? Is the LED by the A/C button on the dash flashing when you try to engage it? Side note: if you discharged the system when you replaced the cycle switch, it needs to be recharged by weight after drawing a vacuum on the system for 45-60 minutes to dry it out.

Here's a couple of schematics for the system. Since you already replaced the pressure sensor, I would be inclined to suspect that either the compressor relay isn't staying closed or one of the temperature sensors has failed. If you have access to a Tech 2 scanner or equivalent, you can do a better diagnosis for what's happening. For example, you can see if the evap sensor reading is within spec. Couple easy things to try if you don't have one: clean the grounds in the circuit, and swap the relay with another one.

Schematic for the compressor controls:

View attachment 370544

And here's one for the front temperature sensors:
View attachment 370545

And the diagnostic procedure:
View attachment 370546

Thank you so much. i will get the man who rebuilt my heads to check it out with his Tech 2.

 

[gpracer1]

Without knowing what the pressures are, my mom's guess is as good as anyones.

 

[rockola1971]

Exactly as GPracer1 said. What are your pressures when compressor is cycled on? What could be happening is you have a leak and most of your refrigerant is gone. Refrigerant is still in the system is heating up which increases its pressure to just above your low pressure cutoff and compressor clutch engages and starts to compress. Then pressure drops below the pressure cutoff and the cycle repeats.