04 Trailblazer A/C clutch not engaging (SOLVED)

[jwalker1970]

SYMPTOM:

04 Trailblazer had intermittent A/C clutch engagement with the A/C system fully charged (showed about 80lbs on low side with engine off)


SOLUTION:

Three wire plug that plugs into the A/C pump has a bad connection on middle pin.

I chased the middle wire with a pick and pushed firmly, the A/C pump kicked in, and out when I released pressure.


Testing the Harnass side:

with relay #44 crossed (pins 30 & 87), with vehicle on or off, and the plug attached, you should have 12V+ at dark green (middle wire), you should have a ground on the black or brown wire, and you should have approx. 5v+ on the Lt Green or yellow wire.



Testing the clutch side: (harnass unplugged)

Black to red 3.7 ohms.
Black to other red 3.7 ohms.
red to red .01 ohms (fully closed circuit)

If red to red open circuit, you have a bad switch on the compressor body---replace compressor.

If red to black open circuit, you have a failed electromagnet in your clutch, relace clutch.

If compressor side tests good, and you are missing 5v+ on harnass side, you have a bad connection.




Hope this helps you. I wasted half of a day figuring this out.

[Schurkey]

Originally Posted by jwalker1970

SYMPTOM:

04 Trailblazer had intermittent A/C clutch engagement with the A/C system fully charged...

...If red to black open circuit, you have a failed electromagnet in your clutch, relace clutch.

I also had intermittent A/C clutch operation, on my '03 Trailblazer L6. A/C cooled nicely when it worked, but sometimes it just plain didn't work.

When it wouldn't work, sometimes the clutch would "quivver" as if it didn't have enough power to fully engage. Tapping the clutch with a rubber mallet would get the clutch to engage.

Discovered that there's no such thing as a replacement clutch. The only way to repair it is to install a new or rebuilt compressor assembly including clutch.

$800, in my case.