Re: A/C Damper Closes Under Engine Load
You maybe already solved the problem, but if not maybe this will help. There most probably indeed is a vacuum leak in one of the lines, because without vacuum the windshield defroster is the default setting. Many times a leak occurs in the engine bay (worn through line or dried out rubber sleeve). I´m not familiar with the ZJ, but try to find the vacuum line, it should be running from the engine intake. Check it very well for wear spots, cracks etc. The ZJ probably also has a vacuum reservoir, so also check the line towards the reservoir.
JEEP Grand Cherokee 4.7 Lmtd 2004
HID 8000K in low and fog / Quad Squad member
Monroe Reflex shocks /
Pirelli Scorpion ATR 245/65/17/
Transgo reprogramming shiftkit.