Blower motor speed

[96expV8]

I have a 1996 xlt v8...about a month ago the blower motor started working only on high speed...researched it to being the blower motor resistor..replaced that and it started working normal again on all speeds. Yesterday it did the same thing again....high speed only...and the new resistor has only been in there a month....underlying problem???? or did the new resistor I put in end up being a lemon????
thanks for any help.

 

[Chikar]

You may have got a bad resistor but the problem could actually be an old blower motor with failing bearings causing it to pull more than normal current.

I just looked at the circuit diagram and it shows the resistor assembly having a circuit breaker symbol. It's likely not a resettable breaker but a fusible link that blows with too much current flow.

You may have got a bad new resistor and since it's cheaper than a motor I'd replace it first. If the replacement blows then I'd change the motor.

 

[96expV8]

Thanks for the reply...
actually the blower motor went out recently also, so i have replaced it w/ a new one...
I guess I'll change the resistor again..since they are only about $13, and see what happens...if it blows again...hmmm....wiring harness????....or if i'm getting too much current flow...what may be causing that??

 

[Chikar]

The motor is about the only thing that could burn out the resistor and since you've already changed it I'd say you just got a bad resistor.

 

[96expV8]

Well, the 2nd replacement blew too...anybody have a clue?

 

[Chikar]

I see it's been about two weeks since your last post. Can I assume you replaced the resistor and the fan worked properly for several days? If so you may well have an intermittent short in the harness.

I've posted a wiring diagram for a 96 in my Public Dropbox folder here http://dl.dropbox.com/u/45028330/air-conditioning-manual-a-c-circuit-1-of-1.pdf

You can download the PDF file to your computer and open it in your PDF viewer. Most people are using Adobe Reader from www.adobe.com .

As you'll see, starting at the top of the diagram, power comes from fuse 6, 50 Amp, in the Power Distribution Box. It then passes through the Blower Motor Relay contacts as the relay is energized when the ignition switch is in the Run position, putting power on the Pink wire with the White stripe to the blower motor. It then leaves the motor on the Brn/Org wire and goes to the normally closed contacts of the High Speed Blower Motor Relay. That relay won't be energized unless you select Hi on the fan speed selector switch on the dash.

The Org/Blk wire carries the power to the Blower Motor Resistor.

It's from this point on you may have a problem with a short or partial short that's putting too much load on the Blower Motor Resistor.

When you look at the Blower Motor Resistor in the wiring diagram you'll see two dark points/spots with a curved line between them. That's Ford's way of indicating a non-resetable circuit breaker in the resistor. If it trips you have to replace the resistor assembly.

I'd think your problem is in the wiring from the resistor to the fan speed selector switch, the fan speed selector switch itself, the wiring from the speed selector switch to the dash selector control that selects where the output air goes (the Heater-AC Control Assembly in the diagram).

Or your parts supplier is selling you less than good quality resitors?

 

[96expV8]

Thanks...man, electrical is not my forte so this may be a stupid question, but, if either of the switches was bad, would the fan and/or the heat/ac not work at all?
one odd thing when the 2nd replacement quit...after i replaced it the fan speeds worked fine..but the next day when i first started out...the low and mediums didn't work...at first..but after a couple of minutes started working and then worked for a couple of days until they finally quit working altogether again...does this provide a clue?

 

[Chikar]

From your description of the results of replacing the resistor the second time I doubt the resistor is bad. The best way to find out for sure is doing a resistance test of the resistor with a multimeter. Do you have or can you borrow a multimeter?

With the resistor electrical connector unplugged you'll be looking for continuity from the resistor pin that connects to the Orange wire with the Black stripe to the pin that connects to the Red wire with an Orange stripe. I can't find any specs that say what the resistance between those two pins should be but as long as you get a resistance reading on the meter you know the circuit through the resistor is OK.

The switches could prevent the fan from running at all but that's not too likely. They have multiple internal contacts and usually it will be only one of them that goes bad so the fan might run on Low, Medium, and Hi but not Medium Hi for example.

If the resistor passes the continuity test but the fan won't run at all, particulary on Hi, I'd suspect either the Blower Motor Relay or the High Speed Blower Relay.

I had to replace the Blower Relay on my 99 and then replace it again about a year later.

 

[96expV8]

since the HI has always and does work I would assume it is not the
HI speed relay.....If it was the other relay gone bad would the LO, MED & MED HI work at all, even after I changed the resistor again...?
also, replaced the resistor again Sat...noticed when i bought the 2nd replacement that it came w/ a limited lifetime warranty!! Hard to believe for
an electrical part...but went and exchanged it..so trying again...works so far...

 

[Chikar]

No, if the Blower Motor Relay was bad no power would get to the blower motor at all in any speed setting.

Were you able to do any of the circuit/continuity tests I suggested. It would be interesting to see the continuity tests on the most recently replaced resistor. If it tests good you've likely got an intermittent problem with your wiring or a switch. If so, the fan may not keep working much longer.

Oops, just noticed you returned the second resistor under warranty. Guess it would be kind of hard to test now

 

[96expV8]

Well, the 3rd one blew so it can't be 3 bad resistors..it's blowing when i first crank the engine and not when i adjust the fan speed...so I guess I can pull off the dash console
where the heat/ac and radio is and look at the wiring to see if maybe there's insulation
worn off and it's touching something and shorting??..the wiring from the resistor under the hook looks intact from what can see.....

 

[budwich]

Your motor isn't "blowing" because of wiring. It's a 12v motor. You can wire it directly to your battery and run it all day and it will do nothing but turn. You have another issue more probably that the blades are getting stuck or something like that.

 

[Chikar]

Hi 96expV8;

Your post, #7 above, mentioned after installing the 2nd replacement all was well the first day but on the second day low and med wouldn't work, then started working later on.

So combining the above with your latest comment that the resistor blows when you crank the engine something is causing a large enough power surge to blow the resistor when the ignition switch returns to the run position and applies power to the fan cirucuit. That could be a frayed wire as you suggest and, and less likely but possible, a bad fan speed switch or bad selector switch (the one that selects Floor, Panel, etc.).

Since you'll have the radio/heater out of the dash anyway to check the wiring it might be worth replacing both switches while you're in there if you can get them cheap enough. Wrecking yard maybe?

Don't ignore the new blower motor itself as a possible cause. Electric motors draw the most power as they start up from rest and continue to until they get up to speed. A dragging bearing could prolong the spin up enough to overheat the resistor and cause it's thermal limiter to blow.

Good luck with this problem. It's intermittent and in my experience with electronics they're the toughest to solve. Always doable, but tough.

 

[White91XLT]

Hi 96expV8;

Your post, #7 above, mentioned after installing the 2nd replacement all was well the first day but on the second day low and med wouldn't work, then started working later on.

So combining the above with your latest comment that the resistor blows when you crank the engine something is causing a large enough power surge to blow the resistor when the ignition switch returns to the run position and applies power to the fan cirucuit. That could be a frayed wire as you suggest and, and less likely but possible, a bad fan speed switch or bad selector switch (the one that selects Floor, Panel, etc.).

Since you'll have the radio/heater out of the dash anyway to check the wiring it might be worth replacing both switches while you're in there if you can get them cheap enough. Wrecking yard maybe?

Don't ignore the new blower motor itself as a possible cause. Electric motors draw the most power as they start up from rest and continue to until they get up to speed. A dragging bearing could prolong the spin up enough to overheat the resistor and cause it's thermal limiter to blow.

Good luck with this problem. It's intermittent and in my experience with electronics they're the toughest to solve. Always doable, but tough.

I would check the amp draw on the new motor, just because it's new does not mean it could not be bad..

 

[96expV8]

ok....haven't done any amp/volt testing...but...all wiring and connectors look good....pulled the console partially off the dash and looked around...NOT going there for the switches.....must be the motor...I looked back at my receipt and it's not as new as i thought....7/11...plus it's an aftermarket...
that's gotta be it...

 

[96expV8]

fyi....it WAS the motor.....knew it as soon as I got it off and tried
to spin it.....replaced and working like normal now....guess that's why
those aftermarket motors are only warrantied for 1 year huh....
thanks for you guys input.....