Air Conditioner and HVAC wiring diagrams

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 response

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.

Thank you sir!

Need clarification on connector B3. Image split through that one with no color or function visible on the second part. So I replaced the relay and the compressor kicked on. Do you think the compressor coil is drawing too much amperage?

Yep, I replaced the relay and it worked I think I will let it run for a bit before I change the compressor out thanks for your time this site is great!

I'm trying to hook a 1996 heater control module to a 1995 control module harness. I need help with the plug diagrams for the 1995 harness to connect to plug from 1996. Or to plug pin out from my harness to the plugs in the back of the new module?

First: Thanks for posting the wiring. My Haynes manual is way off base on these. (Just about everything is wrong there !)

I have a similar but different relay issue.
The PCM is not drawing the ground pin low, so the relay does not turn on. If I draw the relays turn on coil low manually the compressor runs.
I did have to bypass the low-pressure switch to get the compressor to work since the r134 was low, but I am trying to not top it off until I figure out the issue.

My questions are, do you know if these 3-pin high pressure cutoff switches also affect the PCM if the pressure is low since they have a low and high sense wire?
I have good ground at the high cutoff switch and at the low-pressure switch, and 5-volt reference on the gray wire here and continuity on the red wire with black stripe.
I was going to try to bypass the high side switch, but this 3-pin is obviously not as simple to do as a 2 pin and I have no Idea how to bypass that one. Do you?
If this does not also sense a low-pressure cutoff, then I think the issue is between the dash controls and the PCM. The issue is finding this wire since it changes somewhere from white to blue.
FYI: the dash A/C and recirculate buttons light when pushed and the hot cold doors motors do work so power to the control is okay.
On the picture that you marked as fig4 (It is the second row second one in) it shows that wire combo.
Do you know what the heck SP205 in I/P harness is and where it might be?
Thanks

My compressor is not turning on. I need help diagnosing further back than the relay. I can send power to 87 on the relay and it will kick on. I can also ground 85 on the relay and it will kick on. Apparently, the ECM is not grounding it to tell the relay to switch. How do I tell if I have an ECM issue or a climate controller issue?
2003 Yukon Denali with automatic climate control.