These instructions come from a source whose name is lost to time, and apply to many K-based cars from the late 1980s and early 1990s with a separate air conditioner button.
Warning: this repair may result in a broken and hard to repair climate control system. Your car may be different despite the extensive Chrysler parts sharing of the time. Proceed at your own risk.
The purpose is to prevent the car from automatically running the air conditioning compresser whenever the defroster is on. While this can increase your gas mileage, it also reduces the effectiveness of the defroster and does not ensure that the air conditioner is run periodically during the winter (which is needed to keep the components lubricated and the hoses internally covered in oil), so don’t do the modification unless you’re ready to run the a/c yourself at least once a week all year ’round, and to put the a/c on manually when first going into Defrost.
1. Take off the bezel that covers the heater control, radio, etc. On some models (Sundance/Shadow) this is as easy as getting a good grip and pulling.
2. Spread out some paper (newspaper is fine) on the floor to catch anything that falls out in the next steps. Wash your hands.
3. Take out the screws that hold the heater control in. Put them into little cans or boxes. Labelling them as you go is a good idea.
4. Gently pull the heater control just a little from the dashboard; then unhook the cable to the temperature control valve in the heater by slipping the end of the cable off the temperature lever, then releasing the cable sheath from its mounting bracket. There's a catch to this, to make it easy to assemble; it just snaps in. Release it by pushing in the catch with a screwdriver, and it lifts straight up.
5. Pull it out some more so you can get at the back where the air hoses come in. DON'T yank on it to remove it completely.
6. Turn it completely over.
7. Take off the bottom plate by GENTLY prying off the snap brackets on the sides and back. Get the bottom plate off by sliding straight up. Watch for falling springs and clockwork gismos.
8. You can now see that, when you push in the defrost button, a connection is made which moves the appropriate heater flaps through air pressure. (If you are curious enough to try this, hold the spring-loaded bar in place with your other 3 hands. The cams are the alternate-select mechanism which only allow one button to be pushed at a time. The sliding black spring-loaded bar releases the other buttons when you push another, and snap in to hold the selected one in place.) The A/C connection is a U-shaped copper colored slider on the Defrost pushbutton slider. This is what switches the compressor on.
9. Take out the a/c connection (the aforementioned slider).
10. Installation is the reverse of removal.
The parts that might fall out when you do this: If you take the control apart upside down, a bunch of cams, two springs of nearly equal size, and 2 pieces of plastic can fall out. There is a fingertip-sized slider that goes directly in front of the hoses that come in the back. The button on one end fits through the top of the control unit, and when you slide the heater control to one end (Recirculate) it pushes the slider down which shuts off the outside air and you get Max A/C. Clever. There is a spring at one end that's supposed to push it up, without which it will stay on recirculate and you won't get any heat.
All those triangle shaped cams have to be put back inside or the pushbutton system won't work. The slider bar and its spring at one end go over the cams. If the hoses on the back fall off, they are not held in place by the fingers attached to the bottom plate. They are keyed with a pin on the control unit fitting onto the connector. Once you get all the sliders and hoses in place, you can snap the bottom back on, rotate to normal, reattach the temperature cable, rescrew everything back in, and leave it on DEFROST without the air conditioner constantly sucking up power and fuel.
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