The guy making my new wiring harness is almost finished but I'm stuck trying to answer a question.

As I see it:
Within the climate control unit (on a 1984 diesel truck with factory a/c), both the fan and dual fuel selector switches are electric.
The temperature blend lever operates a cable.
The function selection lever operates a valve vacuum selector.

Here's the question:
How/where/when/what signals the a/c compressor to engage?
(I assume it's electrical even though the function lever is vacuum based)

I'm making that last assumption as my engine is a cummins transplant, so while the truck was built with a/c, the compressor is not stock and is located in a different spot.

When I bought the truck in 2004, the engine transplant was already done and the 1st non-stock a/c compressor was installed but had seized up and didn't work. When I removed the damaged unit to access/repair the vacuum pump, I saw no reason to reinstall non-working parts but (key here)I failed to take pictures or make notes of what connections existed at the time. Fast forward to Spring 2011, I replaced the compressor and replumbed/converted the a/c system to the modern coolant. We simply ran a satelite switch to the dash board that I would use to engage the compressor when I moved the selector switch to a/c.

With a completely new wiring harness going in, I would like to integrate the compressor into the climate control system so that the satelite switch is no longer necessary.
When I pulled the old harness, there were a number of "dead end runs" that I had no idea what they were intended to orginally support, so that didn't help answer my question.
Any ideas or suggestions are appreciated.

 

According to the '81 wiring diagrams there is an "A/C Mode Switch" that must be part of the HVAC controls. Coming from it is a Light Green - Purple Hash wire that goes to the A/C Evaporator Thermostat. From there that circuit goes as a Black - Yellow Hash wire to the A/C Clutch Solenoid.

The switch should have 4 connections to it:

• Brown-Orange that is power from the fuse box
• Brown-White, from 2 connections, that provide power to the blower motor
• Light Green - Pink Hash as discussed above

Hope that helps.

 

Thanks for the info! I will check it out tomorrow.