Hi new here,
I've already seached but didn't really find anything helpful. I have a 92 RS 305 tbi. The heater started acting up blowing HTR/AC fuse after running for a few minutes then blew as soon as I tried to turn it on. I checked the blower motor, resistors, switches, everything is fine. But still blows as soon and I turn it on. I recently pulled the dash apart to see if there were any wires rubbing causing a ground short, but I'm kinda lost in there.

I kinda gave up cause it was getting a little cold and wanted to give it another try. Put a new fuse in and ran for half an hour then blew when i shut the drivers door. Put a new fuse in with door open ran fine. Took the fuse out, shut the door, put fuse back and it blew instantly.

Any ideas what could cause this to happen only when i have the door completely shut?

Thanks

 

Welcome to TGO. Reminds me of a problem I once experienced--and this may not be helpful at all (but at least it'll get you a bump to the top). I'd installed a new power antenna and stuffed the excess wiring back into the fender. The wiring worked loose and became caught in the door hinge, causing the a short from time to time. Drove me crazy. Anyway, take a peek.

JamesC

 

alright looked into wires rubbing in the door...got no where, all the wires looked fine not touching together or touching any metal.

there's a ground terminal by the fuse box up a little higher on the body, does the heater ground there, or does it ground somewhere out in the engine bay? I heard back of a cylinder head, is that true

at this point i'm lost...any ideas would be awesome

thanks

 

If you have access too one, it would be better if you used a digital volt meter and measured resistance in wires. There may be a problem that you can not see just by looking at it. You need to measure voltages and resistances in the related systems (probably need a wiring diagram too), to find the problem.....could be an internal wiring problem or the fan motor has very high resistance and is causing the fuse to blow. Sometimes it is easier to it this way than to try to find the problem with no tools. I would guess a short to ground somewhere. Good luck and hope that helps

 

ok so I know enough about voltages to test that, but where/what do i gap for resistances, same as I'd do for voltage?

sorry for the 20 questions, i know nothing about electrical

 

hi...i'm back
thanks for everyones help so far
unfortunatly nothing has worked

today i tested the whole system again, for correct voltages, resistance, the whole nine yards
I finally just gave up and replaced the blower motor to see if that would work
...nothing...

Is there any other problem that'd be causing the fuse to blow the instant i move the selector switch from off?

thanks again for all of your help

 

First question... Are you using a 25amp fuse? If you aren't using the right amp fuse, that alone could cause it to pop.

Here's everything you'll need to fix the problem, right from the book...






Now setting all of that aside, let's look at the circuit. Fortunately the HTR-A/C fuse only controls the circuit diagrammed here. If your fuse is popping, then you KNOW that somewhere that circuit is going to ground. It probably doesn't have anything to do with your door since the wires don't go through your door. You might have a wire with a bare spot in the insulation rubbing up against grounded metal and closing the door causes it to bump together, but that's pretty unusual. More likely one of the devices in the circuit is bad.

Voltage travels from the HTR A/C fuse, to the A/C control head, then to the blower speed switch, then out from the switch to the high speed fan relay, and the blower resistor pack. The final link in the chain before grounds is the fan motor itself.

What this means, is we can start at one end of the chain, and unplug devices to determine were the circuit is grounded. If it were after the motor, the motor would function as normal. Since you've replaced the fan motor, it's pretty safe to assume its something between the fuse and the motor. I'd probably start by unplugging the A/C control head unit. That will eliminate everything except the wiring between the fuse and the headunit. Does the fuse still pop? If so look for a short between the head unit, and the fuse... If not, then try eliminating the switch, and on down the line the fuse stops popping. You should be able to narrow the scope of the problem down to a few suspects.

 

Thanks Drew
The book i have doesn't have that diagram, so that helps tons

Thanks again