Your question is a little too broad? Does the blower motor work? Does it blow cold air, ac? What is the problem?
July, 18, 2011 AT 5:25 PM
Compressor not cycling.
Need to trouble shoot the control circuitry.
July, 18, 2011 AT 7:49 PM
At the compressor relay, terminal 30 is hot/voltage all the time. Terminal 86 goes hot with the key on. Terminal 85 is ground for the coil side of relay, controlled by the pcm. When the relay is energized, that line with the arrowhead, moves to terminal 87, that circuit carries voltage to ac compressor. At the ac compressor, dark green wire is voltage, black is ground. You have to have both.
You might be ahead to check for hvac trouble codes.
July, 18, 2011 AT 8:37 PM
You need to know the pressures on the gauges. The low and high side have sensors that can keep the compressor from engauging. The high side sensor is on the high side hose in between the evaporater and condensor. Jump across the 2 wire sensor to see if the clutch engauges.
July, 18, 2011 AT 9:00 PM
By passed the pressure switches first thing.
Still no compressor engagement.
Will proceed with further troubleshooting this evening with
the info gathered from here, and elsewhere on the web, and
get back to you with further queries, or, (hopefully) resolution
of my problem.
Thank you for your quick responses.
July, 18, 2011 AT 9:06 PM
Let everybody know what you find.
July, 18, 2011 AT 9:35 PM
Go check voltage at the a/c clucth. Reground the negitive wire to see if the clutch engauges.
July, 28, 2011 AT 3:50 PM
Finally got to do some more testing on the Tahoe A/C system.
(My daughter-in-law drives it and between work, school and three teenage granddaughters, it spends most of its time on the road. )
Was able to verify clutch operation and wiring to the underhood relay.
Triggering the relay with a lead connected to 12-v brings the compressor on line and the system starts cooling.
Still cannot get a signal on the control line from the interior.
(This with the pressure switch bypassed. - Btw, I checked the pressure switch with a meter and it tests good.)
Looks like I still need a diagram of the control circuitry in the dash.
This Tahoe does not have the 'Climate Control' version, it is the manual control system.
July, 28, 2011 AT 6:11 PM
Here you go, below. The computer grounds the coil side of ac clutch relay.
July, 28, 2011 AT 8:33 PM
Thank you sir!
Need clarification on connector B3.
Image split through that one with no color or function visible on the second part.