ADSMITH

I have a 2000 Sliverado LTZ Z71 and the s/c is not working. With the a/c turned on max the dash lights show that it is on but the compressor is not engaging. Bypassed the pressure switch and still nothing. There is voltage on one leg of the pressure switch and as far as I can tell all fuses on the side of the dash and under the hood are fine. The truck has had an aftermarket stereo installed and has had the engine swapped. Anyone have any ideas other than replacing the compressor and clutch? Any help would be appreciated. Also does anyone know what vlotages should be where?

oldchevy

Check the wires going to the compressor and see if there is 12 volts there. If there isn't then the problem is not the compressor. If you have 12 volts and a good ground then the compressor clutch is bad.

ADSMITH

There's two plugs on the compressor...one on front near clutch and one near the back of the compressor....should they both have 12 volts?

oldchevy

The one in the front is for the clutch, not sure about the other one.

ADSMITH

worked on the ac a little today and was able to get it to work....well sort if. the only way i could get it to work was by going to the ac relay under the hood and jumping the 2 poles closest to the front of the truck. any suggestions? cooled like a champ when I did that

kevinkpk

Are you getting voltage to the relay coil?

ADSMITH

you lost me a little....relay coil??? i know there is no power to the clutch plug unless i have jumped the relay and that sent voltage to it and it come on and worked fine, but that is bypassing the control switch on the dash. is there a way to test the control switch? and i have replaced the relay with no change. jumped the pressure switch with no change and all fuses appear fine. traced the wired from the clutch to the relay with no breaks. there was a problem with the plug on the back of the compressor. the wiring harness wasnt put back in place correctly and had to splice the and extend the wire a little to get voltage back to there. what does that plug do anyways?

I'm just getting confused and irratated

kevinkpk

The a/c relay is controlled by several things, one is switch on, there are I think two permisssives, one is low freon cut out switch, and over pressure switch. You jumpered out (what I read) are the wires on the relay contacts. Is the relay energizing? If so the contacts are burnt. If not, you need to determine what is not letting it energize.

ADSMITH

what would a bad high pressure switch cause? and can it be checked by jumping it like the low pressure? also is it possible that the contacts thatthe relay plug into may need to be cleaned?

kevinkpk

Permissive is "safe" for the compressor clutch to engage, those would be to the realy coil to engage, thus sending battery voltage to the clutch. If you do not have an over pressure compressor the switch is closed, along with under pressure(freon) switch is closed, with the a/c turned on this allows the relay to activate the clutch. In other words if either switch is "bad" it won't engage the relay coil. I'd suggest you check the pressure in the system even low it can cool with engaging the compressor clutch.