AC System Help

[‘89Jimmy]

Good afternoon,
I've made sure the AC system on my Jimmy is charged, but the clutch still won't grab. I've bypassed the pressure switch with a jumper wire, and still, nothing. The truck goes into a high-idle to account for the load of the compressor, but I'm getting less than 1 volt out of the leads going into the compressor. Fan set to high and max AC settings selected. Any thoughts?

 

[Wes Harden]

There are a number of spade type connection in series for the ac control circuit. A few dirty spades and the resistance really adds up. High resistance can use all the current before it can power the clutch coil. Or worse engage the clutch, but not firmly and allow it to slip, get hot and burn up the disc.
There is a 3 spade thermal fuse on some older trucks with the A6, this is normally after the stepper solenoid, in the control circuit.
Start by de pinning any spade terminals you can, electrical contact cleaner, and brush with SS wire tooth brush. Also clean the ground at the clutch, the compressor bracket is normally the ground it needs to have tight bolts for ground to engine.
if it still doesn't work a simple solution, is to use a relay to power the coil with heavier gauge wire feeding the coil from the battery, using the old control wire to close the relay. This allows the low pressure switch and the stepper solenoid to continue to work as before, and the clutch coil to get full current.

 

[6872xtc]

I would follow the wire from the cycling switch on back towards the firewall to check for any damage.
If I remember correctly, my '90 had the wire rubbing on the cruise control servo bracket. Maybe you have something similar?

 

[Blue85]

The first thing I would check is the clutch ground since it's close and easy and would deliver your symptoms. The idle kick-up solenoid and the clutch are wired in parallel. You'll want to follow the light green and dark green wires around the engine to a weird 2-spade connector where both of these items plug into.

Less than 1V measured across the two clutch terminals? Try measuring from the block or B- to each terminal.

 

[6872xtc]

An '89 should be TBI, correct? So no external idle kick-up solenoid? Uses IAC.
Not that this makes a ton of difference in diag, just clarifying to eliminate any confusion.

 

[‘89Jimmy]

Thank you all! You've given me some great leads.

 

[Wes Harden]

Where did 89 come from ? I didn't see it.

 

[6872xtc]

Where did 89 come from ? I didn't see it.

His username.

 

[Wes Harden]

Duh sometimes miss trees for the forest