GMC Repair: A//C problem, side firewall, gmc sierra

Question
The ac stopped working in my 2004 GMC Sierra 2WD 2500HD 6.6Duramax Diesel.  I have checked the fuse and relay and they test good. The ac clutch turns by hand with light/med. resistance. I noticed the ac clutch does not engage when the ac button(interior) is pushed and the engine is running.  There is no visible signs of a freon leak anywhere.  The blower works on hi med. and low,  but all I get is warm/hot air.  The large and small ac lines are warm.  The radiator hoses entering the firewall are both warm.  Where is the high and low pressure switches located?  Also is there a way to check the pressure switches without harming the computer?

Answer
Hi

Was this a sudden problem, or has it been not cooling good for a while or what, I would ask first.

SOUNDS like your compressor is good.

I would First, check your freon charge.
Most of the LLY code engines had dye in the freon.
I have run into a few LB7, but not all of them. So some had A/C dye added to the freon to aid in the detection of leaks.
The low side switch  is located on the Accumulator, mounted on the passenger side firewall.
The freon pressure switch (high side) is located on the high side line (small diameter line) about 1-2 inches from the top of compressor.
You can jump the low side switch, using a fused jumper harness, but i would not recommend jumping the pressure sensor (a 3 wire switch.)

If so, see if you getting power THROUIGH the low side. Power will come in on the DK>BLUE wire. Black = ground.
If so it is not the switch.
The pressure sensor could be checked with a scan tool, making sure the high side on a gauge closely matches the data on the scanner.
Then I would make sure the clutch is getting power on the DK GREEN wire. Black = ground..
Also the IGN.E fuse feeds the A/C Relay control ckt., so you may just want to look at that.


As for the Blower, down by the passenger feet, is the blower resistor. It has 6 or 7 wire inputs and then the blower motor 2 wire output.
IF you can remove the 7 wire connector, I am sure you will discover the terminals burned.
IF so, you'll need to replace the resistor ($35-$40 range) and the Harness pigtail ($100-$125 range). The harness will come with butt splice connectors. If you do the job, 1 wire at a time and stagger your crimps, for a neater looking job.


I Hope all this helps.
Please feel free to follow post back if needed.
Just advice from experience.
Good Luck
Pawl