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I believe it's the AC compressor cycling all the time. But with the heat on??

 

If you're running your defrost, the a/c compressor will cycle occasionally, just not as often as if you were running the actual a/c to cool down the cab on a hot summer day. This is the cause of that surging idle feeling (noticed especially when applying the brakes how it takes more force to slow the vehicle).

 

The a/c compressor will be engaged in any of the 5 vent selector positions circled in yellow......regardless of where the temp selector is set. If it's doing a rapid cycle on/off, could be low on refrigerant.

 

What is the switch circled in red?

Is this a modification to disable the AC compressor in the modes circled in yellow? If yes what was the modification?

 

AHA! someone else likes to run their defrost without running the compresor and wasting gas!

Just a little FYI for anyone here that hasn't heard this before, the AC cycles on and off to remove moisture from the air before it gets pushed up to the window with the condensor coils. That makes it more effective at ridding your windshield of moisture. However, once the engine is warmed up, you really don't need the AC as the heat generated by the heater via the engine is usually more than sufficient to keep the window defogged.

 

i know this has been a while but, did you tie into the lg wire with a rocker switch, like the one under the control panel?