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Discussion Starter #1
04 WJ limited with auto hvac. Noticed since the temp has gotten in the 40's when set to auto either it blasts heat or cold air. When I set it at say 75 it eventually gets too hot and never seems to stop blowing heat, I turned it down and at about 65 it finally switched over to cool air. It seems that when the outside temps were in the 50-60 it was working ok. Anybody experience this?
 

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The ATC/AZC system can store fault codes that may be helpful. A specialized scan tool is needed for this, a standard engine code reader won't do it.
Make sure that the IR interior temp sensor is unobstructed or hazed over with dirt, nicotine or armor all-type spray residues. It should be located between the zone temp control knobs.
The system can be reset (this will also erase any possibly helpful fault codes) and recalibrated. Remove the IOD fuse. If the fault codes are real, they will come back. Remember to reset your clock when finished.

The HVAC control runs a five second calibration cycle when the IOD fuse is inserted at PDI. If the ignition key is cycled within that five second window, the calibration cycle aborts. The result is a HVAC system that does not accurately measure temperature. Customers may describe erratic temperature control, hot air with AC settings, cold air with heat settings, or different temperature output for driver and passenger from identical settings. The repair procedure is simply to 1) remove the IOD fuse 2) reinstall the fuse 3) wait five seconds before cycling the ignition key.
 

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Discussion Starter #3
Yeah I have read about doing that but been busy at work haven't had a chance to try it. I messed with the system on the drive home and it seems to work but I'm not sure what is normal. I had it set at 75, and after about 20 minutes I had to turn it down to 72, then it would blow cool air from the panel vents, then switch to warm, then cool. etc, kinda annoying but is this normal? I'm accustomed to how a Cadillac system works so maybe Jeeps is just a bit crude? BTW I also saw on the net there is a way to retreive codes and have them display on the control head.
 

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You are correct about the self-diagnostics, I had forgotten this old post:
http://www.allpar.com/forums/topic/121120-99-grand-cherokee-no-heat-passenger-side-only/
 

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Discussion Starter #5
ok I got a 53 and 54, I cleared them and just watched the actuator as I adjusted the temp, by eye it seems to move a bit each time I turn the knob most of the time. when I turn it colder around 70 deg it will go full cold and then go back to warmer, huh?! Well by feel it does adjust temperature ok. Ok so I would like to do a recalibrate, WT *bleep* is the IOD fuse and where is it? I was looking in the underhood fuse box and didn't find it there.
 

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IOD=Ignition Off Draw. It is the fuse that supplies battery power to support clock/settings memory, etc while the vehicle is off. You may see its position noted under the underhood fuse/relay box (PDC) lid.
You can initiate recalibration by disconnecting, pause and reconnect your neg battery terminal. Reset your clock time when done.
P.S.- I also note that a battery disconnect will not erase the old codes. A couple of button pushes does it.
 

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Discussion Starter #7
Ok after some looking on alldata it is fuse #20 on the juction block under the dash.
 
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