#36 Fuse - Consistently Blowing

simutx

Original poster
Member
Jun 1, 2012
2
I have an '06 Trailblazer that has had the #36 fuse (HVAC) consistently go bad during the summer heat. Here is what I have done so far:

1. Replaced the fuse (obviously). When I do, it rarely blows again right away, there is no consistency to when and why it fails. It will fail at start up and while the engine is running.

2. Replaced all of the vent actuators (had to, one of them was allowing hot engine air into the pax compartment...too hot for Texas!)

3. Took the car to a dealership where they tried some troubleshooting for an hour. They were concentrating on the fuse box underneath the rear passenger seat. Unfortunately, this did not help.

4. The fuse seems to blow more when the temperature is above 95 degrees

5. I have also filled the a/c system with additional refrigerant (last weekend). The fuse blew 2x this week.

Any ideas on what else I can try to do to narrow down the problem?

Thanks,

Marc
 

Sparky

Member
Dec 4, 2011
12,927
#36 is labeled HVAC B, 44 is HVAC. My first suspicion was that HVAC B would be the rear HVAC controls, but the rear controls are fuse 13. Then there is fuse 39 which is labeled HVAC 1. What the heck :crazy:

When that fuse blows, does everything quit working, or just a portion?

I'd check various places for damaged or burnt wires first, ones that could short out. The blower motor connector and resistor connectors are high current parts that occasionally burn. I don't know which fuse the blower is on.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Guessing at what fuses do what job is impossible on this platform without the schematics. Might as well not even try. :wink:

It would be best if we knew if the OP has the manual or the digital automatic controls up front, but it's mostly the same.

Rear fuse #36 (HVAC-B) runs the control modules in BOTH the front and rear. Rear #39 (HVAC I) mostly runs the airflow mode and temp actuators. Rear #13 (RR HVAC) runs the EXT rear blower only. Front fuse #35 (BLOWER) runs the front blower.

I don't see any way that the control modules would draw abnormally high current unless they had an internal fault, or the wiring harness to them was routed too tightly past some sheet metal that's cutting into the insulation. If it's that intermittent, and the dealer fiddled around in the fuse block area, I'd do some fiddling around behind the dash and in the console area that goes to the rear control module. Inspect the harness and see if you can spot damage, then wiggle the harnesses and see if you can make the fuse blow. If nothing else, wiggling the harness may rearrange a hidden section of the wiring and make it better. Or worse. Either way, an intermittent fuse problem can be a long and frustrating issue, with a chance you may fix it and never know the true root cause for a satisfying conclusion. Good luck!
 

simutx

Original poster
Member
Jun 1, 2012
2
Thanks for the posts, this thing has been driving me crazy! We have the manual controls for the HVAC system. Roadie, how do I know I am getting to the correct harness, or should I just start shaking different wiring "clumps" around to see if that helps?

Also, when I was replacing the actuators I noticed that there was some toastie burn marks on the wires just past the connection points. Is that typical?

Thanks again,

Marc
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
The correct harness is the one that you trace backwards from its destination at the control module. :biggrin:

Burn marks are only normal on the blower speed control harness connector. Not a good thing, but normal, due to the well-known GM misdesign. Actuators take very little power - no burn marks are normal.
 

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