04 Ac Concerns

miket_99 · June 15, 2009

Have an 04 GMC Z71 with the SLT pkg. The truck has the digital dual climate controler. I am having issues with the A/C working intermittently. If I do not turn the A/C off then the fan off before shutting the truck off, the next time I start back up the A/C will not work. In order to get the A/C back on, I have to turn off the A/C, then the fan, then the truck. This often works, but can take muliple tries in order to get the A/C operating again. I am wondering if the controller might be going out, or if ther is some other switch that might be having an issue.

Any suggestions would be appreciated.

Thanks,

Mike

bill190 · June 15, 2009

These things are quite complex with various electronic (computer) modules controlling this and that. Then all sorts of sensors for various things. You would pretty much need a factory wiring diagram manual to test the inputs/outputs and a multimeter. Also to check that each electronic gizmo is getting its full 12 volts as it should (not a poor connection somewhere).

Then also you would need to be skilled in advanced electronic troubleshooting. Need to understand how all this works as a system, then be able to monitor/test various inputs outputs. If you can do this, then get a GM factory service manual for your year/model vehicle, and test away!

Other than that, your options would be to guess and start replacing things. Maybe start with the main control module. But it could be something else and doing this would be money down the drain. Maybe you could find the same modules at a wrecking yard for not too much?

Or take it to a GM dealer.

flhusa1 · June 15, 2009

open the hood and tap on the low pressure switch. if your ac starts working go to napa and buy a new one. unsrew old one screw in new one and you will have ac. mine did exact same thing replaced low pressure cycling switch and it has been fine. there was a gm tech bulletin on this problem.

medic550 · June 17, 2009

where is the low power cycle switch

miket_99 · June 18, 2009

open the hood and tap on the low pressure switch. if your ac starts working go to napa and buy a new one. unsrew old one screw in new one and you will have ac. mine did exact same thing replaced low pressure cycling switch and it has been fine. there was a gm tech bulletin on this problem.

Thanks, I will give that a try. But I am like Medic550, Where is the low pressure cycling switch located?

bill190 · June 18, 2009

I don't know about your specific year (they like to move these things) but on older vehicles it is on the accumulator which is a metal "can" which the A/C lines connect to. It looks like this...

txab · June 18, 2009

It's on the accumulator

flhusa1 · June 19, 2009

thats where it is. left side of firewall has a plug with wires going to it. just tap on the switch with a scewdriver handle. if the ac kicks on buy a new switch.