TheMongoose

hey gang I need a process to figure out why my fan blows the fuses all the time now for the A/C and heat. I can figure out the electrical stuff if i get some basic directions but know I can't do it on my own. I have a shop manual for the Vette, it's a '76. The 25amp fuse that's under the hood on the PS blows as soon as the fan is turned on. Doesn't have to be on high, just on. I also have a digital volt/amp meter to work with. What do i test 1st, 2nd, 3rd...99th

Thanks in advance, TheMongoose

TimAT

Popping the fuse means there's a short or real high load. Pull the plug off the blower motor and see if it's still blowing the fuse- but don't put a fuse in there. You have a volt/ohm meter- set it to volts, key on, and do the leads across where the fues would go- if it shows 12v, then the short is before the motor. Go back to the resistor on the fan case, pull the plug off that and check again- still 12v, go to the switch. It's kind of a work backwards thing, but you'll find the problem. Look at the wring diagram- build a plan and follow thru.

Theiskell

What Tim said is good advice. One other thing to try, I would ohm out the power wire from the fan to ground with the fuse out. If you see continuity then your short is somewhere between there and your fuse. A black wire runs down to your starter from the ground on the fan, I have seen people hook this ground up to a positive post on the starter. If you don’t know how to read a wiring diagram it looks like the ground would hookup to the starter. Anyway I am rambling that ground wire could have melted and burnt into the hot for your fan. That is how my car was when I got it. Just something to check

TheMongoose

OK, This is great stuff. nothing's simple of course though! I had it working for 5 minutes; right up until I started the car and turned on the heat, at which time the fuse in the car blew.
Sequence of events:
Verified all black wires are hooked to the ground post on the starter.

Found the 25a fuse in the fuse block blown today but not the fuse in the engine bay. replaced the fuse box fuse.
Pulled the fuse out of the engine bay, turned the key on, checked for voltage. no voltage showing. verified voltmeter worked on a D-cell battery. During all the testing I did today this fuse never had power to it? I don't understand this?

pulled the connection at the relay (or whatever's in this aluminum colored box at the top of the above pic). realized this was the wrong set of wires to pull 1st, wanted to pull the power from the blower motor 1st. noticed smoke coming from the blower motor area. smelled burning wiring. turned key off.

located the power wire (purple) and the ground for the blower motor. found the ground very loose. tightened & relocated ground to a different screw on the case. turned key on. Now the fan runs at low speed and there's no more smoke. All this was done with the fan switch in the off position. the a/C controls were set on norm A/c then bi-lvl then vent and it ran at slow speed on all these.
turned on the fan switch and it worked at all speeds.
Started the car, moved the controls to heat so I could see if this would work now. everything stopped working. No power at blower motor now. found the fuse in the car blown again and the fuse in the engine bay was fine.
Out of fuses so I will work on this again after I get some more advice and then run to AdvanceAuto for a pack of fuses.
If you can give me a few clues as to how to proceed I'd be grateful.

TheMongoose

theiskell, I didn't understand what to do for this part? Could you clarify for me? thanx

SIXFOOTER

This step is to make sure the ground wire is good, It is undersized to begin with, so any little flaw will cause the motor to run slow. The ground wire goes from the tab on the corner of the blowrer motor frame to the ground post on the firewall on the corner of the condensor box. From there it is met with a black wire in the engine bat harness ans a braided bond wire that is supposed to be on the valve cover bolt.

From your description it sounds like the bearing in the motor is gone, binding the motor and making it run slow and draw high current. Pull the motor out and see if you can lube the bearings or replace it. they are not expensive.

chvet73

You said something about the ground post on the starter. Others can jump in here and correct me if I'm wrong but I am not aware of any ground post on the starter. There is a ground on the bellhousing bolt. And it is a black wire. My starter has a group of wire joined with the battery cable and the wire that goes to the ignition switch. There also is the wire to the coil. So I'm curious what your grounded to and could that be part of your problem.

TheMongoose

I have 2 orange wires going to one post on the solenoid and a black one coming over the top to a post(u can just barely see it in the starter picture above). So it doesn't appear that anything was hooked up wrong on this end. Can look again if I was in the wrong spot.

The black ground wire from the blower ends up in the wiring going behind the distributor with a bunch of other wires all taped together. It doesn't look like it goes near the starter but everything is all taped up. The black wire off the solenoid goes up next to the engine and then looks like it goes thru the firewall with another group of taped up wires.