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Super Moderator
10,660 Posts
Discussion Starter · #1 · (Edited)
How to install a a/c compressor cut out switch in your Cabriolet.

Parts needed, one butt connector one female insulated spad connector 8 inches of wire.
One lighted accessory switch (3 leads) Doorman Conduct-Tite blue pn Part Number: 85922

Disconnect the negative lead on the battery.

For a detailed Dash Removal Pictorial see:

Remove the switch covers for the headlights, and the switches
Remove the heater control knobs
Remove the fascia.
That is remove the radio, the heater control fascia, the heater blower switch,
Emergency flasher switch the defroster switch, the head light switch, disconnect the parking brake/seat belt warning light.
Remove the 3 top screw for hte fascia surround, and the 3 lower screws on the fascia surround

Carefully remove the fascia surround from the dash.

Remove the 2 screws that hold the heater control selector assembly to the dash.

Carefully you can move the assembly. The Thermoswitch on the left has a capillary tube that is very Fragile.. They are NLA so be warned and Careful.

On the right side of the heater control you will find the white switch with the red/black wires one on top and one on the bottom. It is under the Vacuum Distributor. Remove both wires.

On the back side of the control unit cut the wire-tie that holds the switch wires to the control unit.

Carefully pull the wires to the left side of the assembly and to the switch connectors.

Now take one of the blanks out of your dash Carefully using a hack saw, saw the raised portion off , this will open a hole in the plate to allow the switch to
be inserted. This is a custom fit and filing will need to be done.

Insert the Switch into the new blank hole.

If your switch is lighted then you need to use a ground wire or a power and ground as needed. But a single throw unlighted switch will work as well.
Strip of 1/4 insulation from a 6" piece of wire.
Crimp the female spad connector.

Find the little brown wire from the 4-way flasher lamp.

Go about 4 inches back from the connector and cut the wire in two.

Strip both ends of the wire 1/4 inch.

Using the butt connector attach the gnd lead for the new switch to the brown wire that goes back to the loom and crimp.
Crimp the brown lead from the 4way into the other free end of the butt connector.

Replace the fascia and connect all the switches.

Pull the 3 new wire out to the front of the dash

On the switch you will see 3 pins labeled +12v acc switch +12v and the last one is ground.

Place either of the red/black tracers on switch at either of the 12V points.

Attach the Gnd spad to the switch.

Touch the neg battery cable to the post.

Turn on the keyswitch.

Turn on the fan to level 1

If the switch isn't lit, then turn it on. The lamp should light and the a/c clutch will engage and the radiator fan will turn on,

Now orientate the switch so that when it is on, it is pushed in to the right. Insert the blank (with swich ) in the holder. replace the cover plate.

Tighten the Negative Battery lead.

Hurrah Now you can turn on or off the a/c compressor, works great on cold have heated defrost only....

267 Posts
Hey Briano, this seems like a really great idea. I am planning to do this modification as I slowly redo all of the wiring during my 80 diesel's overhaul. Since my current A/C wiring is not intact, do you have a wiring diagram of what exactly is being wired different from the bentley diagram?

Super Moderator
10,660 Posts
Discussion Starter · #3 ·
No but if you look at your defroster controls, you are removing the wires off the controller (right side) and then placing them on a switch in your dash.
This eliminates the heater on with defrost, and or any of the blue settings.

That switch is depressed in the dash on any blue or the defroster position.
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