1998 a/c compressor problem

[Cappy]

This is a very valuable site and I appreciate any help or advice anyone has to offer.First post for me. I normally use the search to find what I need but not this time.
My truck in a 1998 w/t 6 cyl.
When I push my a/c button the light comes on but the compressor clutch doesn't engage. I have tried jumping the low pressure switch with no luck. When I jumped the relay under the hood the compressor did engage. I thought I found the problem. I bought a new relay and the compressor still wouldn't engage. Every time I jump the relay the compressor engages.
Earlier before jumping the relay I checked the compressor and low side pressure switch for power and found none.
I can't find a a/c wiring diagram for my truck anywhere. I also can't find a detailed description of how the a/c controls work. There is plenty of information for other years and models.
Why (or how) would the compressor only engage if I jump the relay?
Is there anything else I need to jump or test?

I did also notice that when the relay was jumped the air was not cold coming from the vents.

[speedygonzales]

AC Controls page 1

AC Controls page 2

There are 3 control components to the system. The switches and sensors, the HVAC control module (which is part of the switch assy) and the VCM.

The absolute first thing you have to do is see if the VCM is receiving the AC request from the switch. It has to be done with a scanner. Everything else prior to that is a waste of time. Jumping out the relay is a waste of time.

One last thing to remember. There is a low pressure switch, a high pressure switch and the one that everyone over looks. The Compressor cycling switch located on the accumulator.

[Cappy]

Thank you for what you provided speedy.
I am posting a link that I found that best describes the a/c wiring system for my truck. Hopefully it will help someone else if they are looking for a detailed description of the wiring and sequence of events for their air conditioner.
This diagram may not be exactly the same as your vehicle but it provides a lot of very useful information. Well worth looking at.

http://www.justanswer.com/chevy/5d89...ac-worked.html

[speedygonzales]

The one I listed was from the 98 manual. The one you listed is for a 96. So who's more accurate?

[Scrat]

I had similar issues in my '97 K1500 and after traveling the path you went down it turned out to be a loose connector/fitting on the back of the compressor. I cannot find the thread to where i posted it on here last spring, but like i said, it was the little black connector/sensor on the back of the compressor. I just wiggled it and the AC started working again.

I'll update if i can find the thread.

UPDATE =-)

Heres the thread with my AC problem...

http://67-72chevytrucks.com/vboard/s...d.php?t=395595

[Cappy]

Scrat I remember reading your thread this past weekend. That is where I got the idea to try and jump my relay. It's a very informative thread with lots of useful information, especially for someone like me that has very limited experience with automotive airconditioners.
I am finally off work tomorrow so I will be able to work on my airconditioner then. I will post any useful information I run across.

Speedygonzales
Yes the wiring diagram I posted was for a 1996. My truck is a 1998 which is what you posted a wiring diagram for. I appreciate that but I spent a lot of time this past weekend trying to find a detailed description (written) of what happens after the A/C button is pushed in my truck. Your diagram was spot on but the link I posted has it actually written out. That makes it easier for me since I can barely make sense of schematics.