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It's the cold season again...
From an old post...

To make the heating system work in recycle and defrost mode without activating the A/C circuit in a 99+ TJ, I installed a switch in the face of the heater control panel



Tying it into wire C90 20 LG (light green) connector C3 on the right-hand, backside of the control panel. This is the 12v discreet signal for A/C to the PCM and will allow recycle mode with heat only. Just like the a/c on/off switch found in some cars. Another plus to this mod is defrost and feet heat without having the A/C activated. With an automatic transmission (and manual) this also prevents the PCM from cycling the engine idle up/down when in defrost mode, I like crawling rocks and hate that.



Some more help on this; the service manual states that the control panel is not serviceable except for changing the switches on the back.

If you pry up on the clips on the back of the unit, you can separate the housing from the cover, remove the control knobs and open the panel. With the lighting array for the front panel there isn’t a lot of room to add a switch. I located a place to dermel out a mounting hole to the right of the mode select knob to install a rocker switch. Added a disconnect plug to the back of the housing because when you tie into the wiring on the C3 connector with the switch mounted in the control box, there has to be some way of disconnecting the panel from the harness to completely remove the control panel. Or mount the switch somewhere else? HTH



From the research I did, the only thing that tells the PCM to turn on the A/C compressor and increase the rpm is the 12 volt ground (wire C90 20 LG) that is supplied by the mode select switch on the heater control panel. Pulling the compressor relay or installing a switch to control the compressor will not defeat the increased idle function (tried that). This modification has been installed without ill effects…



I did some more research. If you have a 1997 TJ with the slider controls on the heater/A/C control panel the modification is basically the same except for the connector and pin identification on the back of the control panel. The wire number remains the same.

Control panel; connector C218, pin D, wire C90 20LG (light green).

This is from Chrysler document number 80a3b40b J968W-5.

It also looks like 2001-2006 are the same as the 2000…
 
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