HVAC blower issue

[RavenTBK]

A couple months back, the blower decided to take a vacation. Now that its colder, I kinda need more heat than simply driving with the fresh air door open can provide.

Fuse is good. Connection at the fan is clean.

Using http://www.oilburners.net/forums/showthread.php?39256-Heater-blower-problem&highlight=blower+motor <--this thread I did some further testing.

Since the fan speed is varied by the resistor pack through the fan's ground, I tested resistance through the ground wire of the harness side and ground battery terminal.

Ign on fan high 0ohm
ign off fan high 0ohm

ign on fan any other infinite
ign off fan any other infinite

So that tells me the resistor pack is blown, but that still doesnt explain why nothing works, even on high.



Seemingly, I am getting no (+) to the harness side of the blower connector, regardless of ignition, fan, or selector setting. With fuses all good, and such, where should I look next for a resolution?

Thanks. BTW, this is a '90 F350.

 

[OLDBULL8]

Put some 12+ direct at the fan motor, see if it runs. Could be the motor brushes are worn and not making contact. If it runs with direct voltage, then you have to back track for the problem.

 

[RavenTBK]

I thought I covered that in my OP. The fan itself is A-OK. Was the first thing I tried. There is ground through the harness when on high, but none of the others, meaning resistor pack is blown, but it should still work on HIGH. There is no B+ through the harness regardless of switch or ignition position. Fuses are all good, no sign of corrosion or high temps anywhere thats visible.

From further searching, it seems like it could be behind the dash somewhere. Not my forte. I know enough to remove the instrument cluster and thats it. Unless I find some concrete directions, I might end up running a single hot from B+ straight into the fan, and let the blown resistor pack work as an on-off switch.

 

[RavenTBK]

Wasted another day with no results.

I pulled apart the center dash area, undid the four screws that hold the a/c controls in place, and pulled them out as far as I was able with everything vacuum still attached. I pulled the plugs off the blower switch, and am not getting any +12v through them regardless of key or control settings.

Checked the fuse again, its still good.

Jumpered the blower motor again, almost lost a finger when it took off running.

Replaced all controls back into dash, replaced blower motor into housing. Removed and thoroughly tested resistor pack, found the thermal fuse to be blown... cut out and soldered in a jumper. Although I know the resistor pack is on the ground side of the circuit, I figured it wouldnt hurt.

I spent about two hours on the computer this evening searching. Oilburners, FTE, FSB, all without anything useful. Everybody else has an issue with the resistor pack... seemingly nobody has run through my issue.

I am at a loss with this. Desperately trying to avoid taking it to a "mechanic".

 

[RavenTBK]

My GoogleFu is strong most days... but not today I guess. I found this: http://www.f150online.com/forums/hvac/450592-blower-motor-stopped-working-completely.html

This comes the closest to describing my problem, however, this is all about a 2001 F150. Seemingly the 01 has a blower relay providing power to the switch and mode selector before it goes out to the fan. AFAIK, the '90 does not.... or does it? Anybody know? If so, wheres it at?

 

[w4dsb]

even with the reisitors on the ground side they will be hot because they are burning the excess voltage off as heat thus lowering the speed. maybe the motor is dragging some causing higher current and higher heat causing the thermal to blow