Jeep: 1999 Jeep GC A/C issues, amp fuse, horrible service

Question
As I was driving my Jeep today in the unbearable heat with my A/C on HI, it abruptly shut off and stopped working - completely!  I have had a chance to reading some of your advice and possible solutions to similar problems, and have tried most of them.  1) - Checked fuses under hood and under dash -- all appear good.  2) Pulled harness near blower motor -- doesn't appear to be "fried" what-so-ever(red wire looks good). Wiggled harness as well with A/C on -- still nothing.  Before i take the vehicle into the shop, any other solutions that I should try that could be a "quick fix"?

I also inherited another issue while checking/switching fuses...when I switched the 40 amp fuse to the blower motor to see if that was the issue, my check engine light came on.  Not sure why.  Any ideas?  Any insight or advice is greatly appreciated.  Thanks.

Answer
Hi Alan,

First, I'll assume it was the blower that stopped, on all speeds? Also, it's imperative that you not hear the blower motor running, in addition to no airflow. If you have dual zone A/C (AZC), which I assume, I would still look at the Blower Control Module, since they had a horrible service history. Pay particular attention to the thick red wire *right at* the connector -- if there is discoloration or swelling, there's a good chance that the harness needs replaced (or if you read my previous posts on this, just the pigtail) in addition to the Blower Control Module. Unlike most systems, even the high blower setting runs through this controller, so if it goes bad, all speeds are down. In actuality, the Control Head feeds the module a Pulse-Width Modulated signal on one wire, where most manual systems contain a wire for each speed, to a Resistor Block. If you have the manual system, and lost all speeds, then this normally isn't the problem.

I also assumed that you've seen maxi-fuse #1 in the PDC, and tried swapping that with another device? If you've done that, and the key was on, then you've probably kicked up an error in another system. ONLY swap fuses and relays with the key OFF after 5 seconds, unless you know the entire circuit. Regardless, the error will clear soon if it was erroneously set.

It was a good idea to to go to power distribution, since Fuse#1 does provide power for the blower motor itself (in manual systems), or the module (in AZC). These systems actually work by providing ground to the circuit, basically. Rarely have I seen the motor itself fail, although that's a possibility, and any Control Head issues always seemed to be a complete shutdown (in yours, JUST the blower, right??) or a variance in the accuracy of the outlet temperature. The only other grave problem is the Recirc or Blend doors breaking, but you'd hear issues with that, even if it managed to block the entire passage.

One last thing: although it's way too involved to explain here, the AZC head does have a diagnostic function. Holding the A/C and Recirc buttons at the same time, rotate the left temp control knob one click to the right (CW). Release the buttons, and wait for the display. If no fault codes are stored, then it will display a '00'. '01' -> '32' indicates a current fault detected by the controller, while anything '33' and up means a code is recorded in history. Rarely do the history codes do anything other than direct you to a point of inspection, and even current codes only point to an area of the problem. Even so, this is really only a self-check for the control head -- moving the knob another click can get you to HVAC System Pointers and Tests, but I'd have to write a book to describe all that goes on. To exit, simply turn the system OFF.

I hope some of this helps, and in any event, good luck!