REALLY strange A/C issue........any GM techs on the forum?

[Devillusion]

Ok, try to make a long story as short as possible.....

Installed my cold air intake, started up the truck and gave her a couple good revs (4500 rpm) to clean out the throttle body as I had cleaned it out as well in the process.

NASTY loud squeal/steam engine sound (really loud) happened, killed the truck with the key instantley. Having no clue what the hell it was, started it up and was fine. Did it again....same thing happened. Left the truck running this time and noise went away. First thought was a bearing in the pulley/tensioners etc. A/C clutch was engaging and sounded funny to me so assumed I had maybe created a high side and blew out a hose or o ring etc.

Started it up to look at it again in the morning, compressor wouldn't engage.

Took to a shop, reclaimed all the refrigerant, pressure tested, and refilled with no issues found on that end. (was down 3oz of refrigerant...nothing really). A/C still did not work.

They checked the power going to the low/high pressure switch...nothing there, went to fuse....was good, even changed it to be sure, checked relay under hood....good.

Jumped the two terminals on the relay for the a/c under the hood and everything cycles and blows ice cold with no issues says that it is working perfect on that part. Says that he went throught he wiring diagrams and figures that the "a/c module" is the issue (under the dash somewhere? but was not sure and not crazy about getting into it cause he was not familiar).

Heat and everything else is fine, no appearant codes etc. Says that if the module is replaced will need to go to GM dealer or someone with a tech 2 to relearn to the body control module. If at all possible not taking it to our local GM stealership...cause they are crooked as hell. Know someone with a tech 2 so not an issue but would like to figure out and repair myself if possible.




Anyone have any experience with this type of situation? Any help appreciated.

2003 GMC 1500HD with full load digital dual climate control etc. 6.0L auto 4x4....

[clinebarger]

The A/C control head in the dash IS the A/C control module.
An Original '03 control head works different on the "snowflake" light, If there is a slash though the symbol...The A/C is off....

The A/C control head sends a "A/C request" signal to the PCM, The Low Pressure Switch sends a ground to the control head anytime pressure is above around 25 psi, If the control doesn't get this ground signal....It will not make an A/C request to the PCM.

The PCM controls the A/C Comp relay & monitors "high-side" pressure with a pressure sensor. If pressure is to high or low.....The PCM will inhibit compressor operation.

The First! thing to do, Is to see if the PCM is getting a A/C request from the A/C control head.

[sleepertruck72]

Did you ever get this figured out ? If not I would hook up the tech 2 scanner since you know someone that has one... in the data display it should tell you if the A/C relay is "on" when you press the A/C button ... That would be a real quick way of knowing if the signal is there...

[Devillusion]

Ended up being a hit and miss pressure switch, intermittent issue. Buddy just got lucky and threw the tech 2 onto it and gave it the command to turn on and the signal was there, then wiggled the switch and would work. Wish I knew that before....would have saved myself 200 bux in the shop... ugggh. lol.