On my '00 XJ 4.0 AW4, the engine RPM kept surging up when at idle. I determined that the AC compressor was cycling on and off no matter which position the HVAC system was set to ( I know the AC comes on when in defrost mode). This happened at approximately 45 second intervals. I pulled the AC relay and the compressor no longer cycles (and my AC obviously doesn't work). Do I just need a new relay or is it something bigger?
Carl
FWIW, it cycles even when on Hot and Vent, and not in the AC position. The AC does blow cold when in the AC mode.
Carl
It's either the dash blend assembly switch or a malfunctioning relay. Test the signal lead from the dash selector with a voltmeter first (switch between vent and A/C and check for 12v signal), and if that checks out, then the problem is most likely the relay.
I've never seen what the relay looks like. If it's like the older mechanical types, it's possible to clean/repair it instead. I've done this with mechanical voltage relays in the past.
Maybe it was the fuse I pulled. It was in the engine compartment fuse box.
Carl
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