Bronco Forum - Full Size Ford Bronco Forum banner

1 - 13 of 13 Posts

·
Registered
Joined
·
262 Posts
Discussion Starter #1
1990 Bronco, 302

Issue: Blower motor works intermittently. Will sometimes go for weeks with no problem, then suddenly quit for a few minutes, hours or days.

When it works...it works fine, when it doesn't...it is as if there is no power to it or the circuit that feeds it?

What I've done:

1. Of course, checked the fuse first then the blower. Disconnected the harness to it and directly applied 12 volts to it, motor works fine.

2. Harness connector was brittle, so I replaced that and also cleaned the terminals it houses. Applied dielectric to each terminal. Just maintenance.

3. Replaced the Resistor while I was there...since it looked to be the original and it was pretty dirty.

4. Looked at the fan switch (dash), the harness connector there was slightly burned looking so I replaced it and the switch.

5. Put the 'selector' though its paces (when the motor WAS running) and it performs as intended.

I am not aware of any relay in that circuit, but I could be wrong. I have a full service manual, but it is somewhere in storage right now.

I'm guessing that circuit gets its power through the ignition?

I don't think I have a ground problem...but am willing to entertain any ideas.

Thanks guys.

And Yes I 'searched', been here long enough to know the search police will come out if you don't. :)
 

·
Registered
Joined
·
18 Posts
Mine did this and it was a tarnished fuse. Fuse not blown but old, replaced with a new one and no more intermitent problems.
 

·
Registered
Joined
·
262 Posts
Discussion Starter #3
Thanks Steve.

That first link reminded me that the fuse in that position did indeed show signs of being hot (resistance). I had replaced it some time earlier and forgotten about that. Not as bad as the one pictured in the link, but clear evidence something is amiss.

Looks like I will need to pull that fuse panel and look at the back of it, as well as the wiring leading to it.

Appreciate your efforts Sir!

Flint.
 

·
Registered
Joined
·
262 Posts
Discussion Starter #4
Update

Pulled the fuse panel, fuse connection at that location slightly burned looking (though the fuse itself was not blown). Probed the Brown with White Stripe wire leading to the that A/C fuse (30 amp) and it was dead as could be.

Followed the wire as far back into the dash as I could see, but did not see any obvious breaks in the wire.

So I stripped that wire back (just behind the fuse panel) jumped a short wire from another location on the fuse box to the 'dead' Brown/wht wire and BINGO...blower motor started up. Moved the 'selector' through all of its positions and the fan speed switch as well. All worked as intended.

Not sure WHY I don't have power from that wire, but my short term solution is going to be to run a separate (fused) wire directly from the battery to the wire from the fuse box. That will give me power to that circuit again, just by-passes the fuse panel. I will fix it properly later when I have time. Meanwhile....(this is a Ranch Vehicle), I will have A/C and Heat again.

REALLY hot in Texas right now. There isn't a 'Sweating Profusely' smiley to post, or I would.

Flint.
 

·
Super Moderator
Joined
·
26,048 Posts
YO;
90 Bronco 5.0 Blower ckt wiring diagram

See more diagrams and in full TSBs

Following for 92-96 Bronco, but similar to your 90;

operating speeds are controlled by a heater blower motor switch resistor connected in series with three of the operating positions and the ground
With the heater blower motor switch in its LOW position, current flow in the ground circuit passes through three of the coils in the heater blower motor switch resistor. In MEDIUM LOW, current flows through two coils. In MEDIUM HIGH, current flows through one coil. In HIGH, current flow in the motor ground circuit bypasses the heater blower motor switch resistor to provide maximum speed.
 

·
Registered
Joined
·
262 Posts
Discussion Starter #7
that is one of the main power wires, you really need to figure it out. It usually runs out to the underhood fuse box and connects in there somehow.
No fuse box underhood, just a few relays. But yes, I WILL repair it correctly when I have the time and the temperature is more favorable.
 

·
Registered
Joined
·
262 Posts
Discussion Starter #8
YO;
90 Bronco 5.0 Blower ckt wiring diagram

See more diagrams and in full TSBs

Following for 92-96 Bronco, but similar to your 90;

operating speeds are controlled by a heater blower motor switch resistor connected in series with three of the operating positions and the ground
With the heater blower motor switch in its LOW position, current flow in the ground circuit passes through three of the coils in the heater blower motor switch resistor. In MEDIUM LOW, current flows through two coils. In MEDIUM HIGH, current flows through one coil. In HIGH, current flow in the motor ground circuit bypasses the heater blower motor switch resistor to provide maximum speed.
Thank You Sir,

I greatly appreciate how you always take the time to help folks and provide information. You are an asset to this community. :thumbup
 

·
Super Moderator
Joined
·
26,048 Posts
Thank You Sir,

I greatly appreciate how you always take the time to help folks and provide information. You are an asset to this community. :thumbup
YP Flint,

Thanks!

BUTT really I have been an asset at times.:rockon
 

·
Registered
Joined
·
262 Posts
Discussion Starter #10
Arrrghhh!

O.K. guys, revisiting this again. (90 model bronco), previously, no power at the A/C fuse location.

For some reason...when I supplied power to the wire (brown w/white stripe) that goes to the 30 amp fuse for the A/C, my battery is being drained of power overnight. I brought a fused wire directly from the battery and tied it into the wire going to that fuse location.

The fan and speed functions seem to work correctly, but I have to wonder if I am 'back feeding' this circuit somehow?

The fuse terminal is now hot at all times, regardless the key position. In fact I can remove the fuse from the fuse block and I still have power at the hot wire lead to the blower motor (provided the selector switch is on).

I don't see that as a problem...except it suggests I am feeding the fuse block (buss) and it is draining the battery somehow?

I am not very good with electrical (obviously). Is it perhaps a shared circuit?

Or am I way off base?

Thanks, Flint.
 

·
Registered
Joined
·
415 Posts
YO;
90 Bronco 5.0 Blower ckt wiring diagram

See more diagrams and in full TSBs

Following for 92-96 Bronco, but similar to your 90;

operating speeds are controlled by a heater blower motor switch resistor connected in series with three of the operating positions and the ground
With the heater blower motor switch in its LOW position, current flow in the ground circuit passes through three of the coils in the heater blower motor switch resistor. In MEDIUM LOW, current flows through two coils. In MEDIUM HIGH, current flows through one coil. In HIGH, current flow in the motor ground circuit bypasses the heater blower motor switch resistor to provide maximum speed.
are the resistor coils located in the switch? I have had a couple trucks that the fan only worked on hi but because it was just a shop yard truck and it did kinda work I never looked into what the problem actually was. I think the 96 F150 I just picked up may be doing the same thing.
 

·
Registered
Joined
·
262 Posts
Discussion Starter #12
are the resistor coils located in the switch? I have had a couple trucks that the fan only worked on hi but because it was just a shop yard truck and it did kinda work I never looked into what the problem actually was. I think the 96 F150 I just picked up may be doing the same thing.
No the resistors are a separate component mounted just below the Fan Motor. Not my problem (perhaps yours). I have ALL fan speeds (always have) and my selector switch (modes) also works correctly.

My issue was...I had no power at the 30 amp fuse slot for the A/C (which also controls my blower). So for a short term fix...I ran a fused wire directly from the battery and tapped it into the original Brown w/wht striped to make that circuit hot again. Everything works fine, but for some reason it (or something else) drains my battery overnight.

IF I disable that circuit (pull fuse or disconnect from batt) the battery holds its charge just fine. I have pulled the fuse from the fuse block (since the circuit is hot now even without it) to see what happens.

If its dead in the morning...we will try something else. I just don't have the time right now to trace the original wire back through the firewall and test all the connections. Need to have the fan working...to defog, defrost the windshield.
 
1 - 13 of 13 Posts
Top