Fuse pops when heater/AC turned on. 89 burb 6.2 diesel

[buckallred]

Hi:

The fan suddenly stopped working. I figured out that it is because the fuse is popping every time I turn on the heater or AC or defrost etc. It's a 30-amp fuse. 89 burb 2500, 6.2 diesel.

This happened fairly suddenly and for no obvious reason. I've replaced the fuse 2-3 times and they keep popping. It has been wet and rainy here. Everything else seems to be working fine. All lights, dash lights, stereo, interior lights.

Is there any advice, and specifically any hope of an easy fix? It's nearly always a grounding issue, as I understand it. I appreciate all advice and help. Thank you.

 

[ccj8008]

You have a hot wire going to ground somewhere. Probably cracked insulation. You can trace it or replace it. Had a similar issue with my cigarette lighter.

 

[Wes Harden]

Inspect the wiring at the hi blower relay and the purple wire from the relay to the blower motor. If the wiring looks good unplug the blower motor, new fuse, and turn the heater on, with fan switch in any on position. If fuse doesn't blow replace the blower motor. If it does blow disconnect the relay's fatter wires and try again.
The relay will be on the passenger side under hood. Attached to or near the evaporator case.

 

[buckallred]

How big a project is it to replace the blower motor? Is it reasonably easy to access with an air conditioner and all that? I haven't even bothered to look. Thank you

 

[Wes Harden]

Is not horrible, 1/4 drive sockets and ratchet there are a couple of tough screws bottom fender side. magnetic socket help go back together. When you get your blower motor get a new squirrel cage. Your will probably not survive being removed and installed on new motor

 

[buckallred]

Thank you all for the advice. I'm betting the blower motor finally gave out. 1989 vehicle, original blower motor as far as I know.

I will test the procedures above and report back. And if I put in a new blower motor I'll definitely do the squirrel cage too.

 

[buckallred]

Replaced blower motor with squirrel cage. Initially the fan worked, it was making a weird whining noise, but it worked. Then when I switched the A/C on, the fuse immediately popped.

So it's not the blower motor. I glanced at the wires including the purple wire mention. There was nothing obviously wrong with it.

So it must be something up under the dash? What about the large gray / metal fuse or relay thing contained in photo 3 (and 4)? Thanks!

 

[dyeager535]

So you tested without the fan as suggested and the fuse didn't blow?

You should probably test the load side of the fuse cavity with a multimeter set to continuity to first ensure there isnt a short to ground when you switch it to AC (instead of just wasting fuses).

If it's a short to ground, it's pretty easy, you unplug things on that circuit until the meter doesn't indicate continuity to ground.

Not overly sure what all is in the AC circuit, but you've got a few electrical components and a fair bit of wiring that can have issues.

IMO best idea (after conducting a good visual inspection) is to ensure it's not a short to ground.

 

[Wes Harden]

Replace fuse, unplug ac compressor at fan belt clutch. Retest.
Shouldn't be squealing if new motor and squirrel cage. Though sometimes if the cage isn't perfectly balanced or rubbing on the case it might

 

[Blue85]

Basically follow that 66 LT GRN wire - that's the thing that's only powered in the AC modes (you can see which ones where the switch is shown). It's interesting that a diode is shown at the compressor clutch. I don't know if that's in the connector or in the clutch assembly, but if you get that backwards it will pop the fuse. Wouldn't be surprised to see a wire chewed up at the front of the engine there. You can also break that circuit by pulling the connector off the pressure switch mounted to the receiver/dryer can.



You're popping 20A fuses in the HTR A/C slot? As mentioned above it could be a combination of the blower drawing too much, plus the clutch engaging. There are only those 2 loads on the circuit (if it's per the diagram above), so with the clutch and blower unplugged a DMM should read open circuit at the fuse block.

 

[Wes Harden]

The diode is at the compressor coil plug. should be crimped from factory. Though I have seen them mia. Mine was and I needed to replace it.