My front blower stopped working in the high setting at the same time the rear blower totally stopped working. I noticed both of these were on the same 50A fuse which was blown so I though bingo - bad fuse. Well I put in a new fuse and it immediately blew so I am thinking a short or possibly bad resistor.

Anyone have any ideas were to begin my troubleshooting? The front blower and AC works on all but the highest setting, and the rear blower does not work at all. The fuse blew as soon as I put it in even with all of the blowers off.

Thanks Scoop

 

One of your blowers is likely bad or going bad. Depending on the year, for the front blower, speeds other than high go through a resistor, and the power may route through the switch itself. On high, the resistor is bypassed and the blower relay engages to route power directly to the blower. So high speed is the only one that pulls full power through the fuse.

On the gmt400 series, the blower relay is either in the panel by the driver door, or under the hood. On the gmt800 the relay and resistors are integrated together. Knowing the year makes a big difference.

Personally I would pull a wiring diagram for your year vehicle from https://charm.li and I’ll bet that both blowers share that fuse, but have different speed control resistors and relays.

 

Thanks for the nformaton. I will check out the diagrams and see what I can find out.

 

Also check for a short in the blower wiring. You never said what year vehicle we are dealing with here, but my 1996 C1500 has had some wiring issues lately, including in the blower circuit, and some broken grounds.

 

OK thanks its a 1999 3/4 Ton 7.4L.