HVAC Fuse Blows, No Blower Motor

[rlmarz]

I had taken my 2012 1500 into the dealership (separate issue, my mechanic nor I was able to diagnose, either was the dealer) earlier this week, but on Tuesday morning had no airflow at all. Single temperature control, both the fan speed light and AC light were on. My aftermarket backup camera was no longer working either. Honestly, none of the work the dealership did should affect any of this, I'm in agreement with them on that.

Some troubleshooting later, blower motor works fine on 12V. Blower motor resistor was corroded to hell which I thought was my smoking gun. Once replaced, still no joy. The J15 (Front HVAC) fuse is popping as soon as I try to turn the fan speed on. The front HVAC relay is clicking as it should. I'm looking for a wiring diagram or any assistance in troubleshooting this, hoping it does not turn into an electrical gremlin and I don't melt before I figure this out. Thanks all.

 

[Firetruck41]

You have done some of the things I would, to trouble shoot. I would post what the work was that the dealer did, sometimes things that seem unrelated, might be. The coincidence of the timing suggests that.

 

[rlmarz]

Brake transmission shift interlock recall and diagnosing a brake issue (assumed to be master/booster related).

The rain is keeping me from reattacking at the moment, but I'm planning to troubleshoot/replace the backup camera once able. It would be nice if I found some pinched wires or something of the like, but I'm not hopeful.

 

[rlmarz]

Update: The camera wire was disconnected on the frame rail and tied in a knot. Unrelated to the AC, but very obvious 'they didn't touch it'.

 

[rlmarz]

Tested the relay and points sat. Key on with the blower motor and blower motor resistor disconnected results in a blown fuse. Im thinking a short in the selector knobs is the next reasonable place to look.

 

[NETim]

Tested the relay and points sat. Key on with the blower motor and blower motor resistor disconnected results in a blown fuse. Im thinking a short in the selector knobs is the next reasonable place to look.

I think I'd want to ohm out the 12v power wire to ground at the blower motor connector. I'm betting it's a dead short. A wire is pinched somewhere or the insulation has been damaged on the 12v line.

 

[rlmarz]

Definitely a wiring issue. With the dash disconnected she still blows the fuse immediately. If I've got my flow right, it's 12V fused to the relay, switch, resistor, motor. With every component disconnected I have to think it's somewhere between the fuse and dash.

 

[dwhutch]

Is there any way to get hold of the TSB related to the recall? If you can find out what the recall entailed you might find where a wire may have been pinched. I've seen wires pinched by techs when covers or components are removed and reinstalled many times in my 40 plus year career. Sometimes the insulation isn't broken immediately but happens later due to vibration. I'm guessing your trip to the dealer is the root of your problem but I could be wrong.

 

[rlmarz]

I've had no luck finding such documentation or a wiring diagram or the TSB. It is listed as the transmission shift interlock T79. I'm afraid I don't think there's much I can do with the dealership anymore given it's been a week. They swore off having anything to do with the issues I was having. I'll be taking it in hopefully tomorrow as I've exhausted my troubleshooting efforts.