Hello, hoping to get some help for my Cobalt, the blower motor stopped working and I found the BCM3 fuse was blown. I replaced it and it blew again (of course it did). I have verified the blower motor is good, I also have verified the resistor is good. I did a test on the HVAC relay and it tested good. With the blower motor and resistor unplugged the BCM3 will blow when the ignition is turned on, if the HVAC relay is removed the fuse will NOT blow when the ignition is turned on. I'm not sure if this helps with the diagnosis but it is what I know so far. Any help would be appreciated, Thanks

 

Interesting story. Maybe someone on the Cobalt forums could help.
Has anyone done any electrical wiring work? On an HHR there is a diode in the under hood fuse box that might cause that. Does it blow no matter what is turned on? Do you mean the HVAC relay on the BCM or the AC clutch relay under hood? It is a straight shot to the blower only when it is energized, so if the blower is not turned on it is connected to nothing.

Anyone install LED lights? If wired incorrectly they are a switch that will cause a dead short.

My guess is someone that assumed all red is 12v and only black is ground messed with wires. The blower has a brown wire for 12v and the orange goes to the switch that chooses a route to ground through the resistor pack. Thjere is a signal wire fron the blower switch that informs the BCM if the blower is on or not as a condition for turning the compressor on.

 

Thanks for the reply. Im pretty sure there has been no electrical wiring work. Yes the HVAC relay on the BCM is the one I'm referring too. The car does have some LED lights, the headlights and I believe the blinkers. These LEDs have been on the car for quite some time. Would they cause a dead short in a relatively short amount of time? The LED headlights have been on the cars for 6+ months and the blinkers have been on the car for 2 or more years.

 

I was meaning more like "ground effect" and interior lighting LEDs. No newly installed sound equipment? No fuse taps?
Does the fuse blow if you start the car with the blower turned off? If it does the problem is in the relay or the fuse box if not, between the relay and the switch.
There are crossed wires in the blower circuit somewhere between the BCM fuse box and the blower switch.
If the resistors are bad the blower runs but only on high. There isn't supposed to be any + wire after the motor in the circuit. Maybe some how 2 or more connectors on either the switch or the resistor pack are making a circuit.

 

Get the wiring diagrams and I can help you.

 

The wiring diagram has been posted many many times. It is simple, I laid it out previously.
The Cobalt is the same as HHR in this aspect.

BCM3 fuse goes to the relay always hot. When the blower is switched on the BCM energizes the relay sending 12V to the motor. The ground side of the motor goes directly to A. the high resistor and B. the high pin on the switch. The switch then selects a path to ground through one of the other resistors.
Connections on the switch are
high
3
2
1
off
ground the center of the switch
signal to enable AC
There is NO power being supplied to the motor circuit unless the relay is energized.
So, if the fuse blows when the relay is NOT energized the problem is in the relay circuit
If it only blows when the relay IS energized the problem is in the blower/switch,resistor circuit.
If the resistor pack fails only high is available, since it goes directly to ground bypassing the resistors.

It is not unheard of that the internal contacts of the fuse box get fried.