A/C, Heater blower fan doesn't work

przeho · March 2003

Hello,
My interior A/C, Heater fan doesn't work. I've checked all the fuses, interior and under the hood, and all are ok. I've removed the fan and hot wired it to the battery and it worked. I've also checked the resistor with a multi meter and it show's that it's ok. I've also removed the dash to check the fan switch and it was ok. I'm lost as what to check next. Any suggestions are welcome. The dealer wants over $50.00 an hour and I would like to save some money and fix it myself.
Thanks, Paul

swschrad · March 2003

get a test lamp and a long wire to reach around the car and under the hood, and start tracing and testing the wiring between the parts, then. that includes all ground points.

the a/c may have a limit switch that shuts off the fan. there may also be a set of outputs from a general-service electric module... aka a power control module.. that are part of the circuit. these modules are not without failure, and they are priced without modesty

a wiring diagram for your can may help. if this is the focus you also ask about in other discussions, and there is warranty left, get what you can and let the dealer charge Ford $50 an hour.

przeho · March 2003

Scott,
Thanks for the info. I should have mentioned that this is my 94, 1.9 liter Ford Escort Wagon. The car has been great except for this blower fan problem. Do you know where the general-service electric module... aka a power control module is located. It looks like it's time for me to get a repair manual for this car.
Thanks, Paul

swschrad · March 2003

it might be direct wiring like in the golden olden days. one more thought... as you trace the wiring, you might come across a detour into a relay box, and a funky relay is definitely a suspect in this kind of problem. check your fuse boxes including the underhood one... if you have relays, and the owners manual indicates one is for the fan, swap it with a similar relay and see if your problem goes away. if so, get'cha another relay... in fact, get two, get a handful if you have to get 'em from a junkyard... and then Murphy's Law of Spare Parts says you will never have another relay problem again.

przeho · March 2003

Thanks for the info. I'll check it out tonight. I hope it is a relay that went bad.... Looks like an easy fix if it is a relay.... Paul

delivereguy · April 2003

Thought I would check to see if someone else had this problem and well yes, someone does! This is a 94 Mercury Tracer. I pulled the motor and hooked it to the power source in my other car and the motor works fine. I checked and the 30 amp "circuit breaker" is ok. So I pulled the resistor pak, but not sure if that is working or not. It maybe a good suspect, so may go to junk yard and get one and see if that does it. Yeah, I was also wondering if there might be a relay in the circuit somewhere??? Thanks........

przeho · April 2003

I posted the earlier message and mine still doesn't work. I tried to trace the wiring but had no success in finding the problem. If you do get yours working again, post the solution or send me some e-mail. I'm going to see a mechanic next week so if I get mine working I'll post a reply and let you know what the fix is.
Paul

0patience · April 2003

It is located on the heater housing, will have a plug in attached to it and is held into the heater with 2 small screws.

swschrad · April 2003

blower resistors aren't that expensive, either. so if you don't have a multimeter to check the resistance, at this point, change it on general principle and see what happens. three weeks after I bought my 2000 explorer, the blower resistor went out. in that case, cheap part and lots of labor to get to it.

opera_house_wk · April 2003

Ford has a thermal fuse. This little metal cylinder part is the same as those put in hair dryers to turn it off in case air flow is blocked and the resistors get hot enough to start a fire. Being chemical in nature these sometimes go bad with just age. They are available at all Radio Shacks for under $1.50 and are best crimped on. If soldered, the leads must be heat sunk with a pliars or they will blow from the heat carried up the lead from the iron. If you feel lucky and have good insurance, you can just jumper it out.

0patience · April 2003

Ford has a thermal fuse
Well, not really a fuse.
There are 3 coils, each provides a certain amount of resistance and there is a diode in the circuit.
Location and what it looks like.

delivereguy · April 2003

Opatience, yeah, that is exactly the part I am looking at!.... Ok, a check with a multimeter shows different voltages through the different coils, but no voltage through the diode. Looks like that is the culprit...Is it possible to just replace that diode??? Thanks for your help....

0patience · April 2003

Hold on, if it shows a voltage drop, then the reg may not be your problem.

Is it possible to just replace that diode?
I suppose you could replace just the diode form one at Radio Shack. But unless you get the right one, you may create some other problems.
And a new resistor is less than $15.

Ok, back to your problem. Look at the image I linked to again, I added the connector view.
On Terminal 2B, with the fan switch on, do you have power?
In low, med and high, do you have power and if so, what is it?
If you have power at that terminal and it is different in each position of the switch, then check the terminal on the fan motor.
Let us know.

opera_house_wk · April 2003

The part is a thermal chemical fuse. A chemical reaction takes place at a certain temperature and eats it open. Look on the outside printing and it will give the temperature.

0patience · April 2003

So explain to me why there would be a fuse between the low medium circuits on the resistor.
The design is to drop the voltage and not feedback to the other circuit.
A fuse will feed either direction, where as a diode only goes one direction.
Most of the schematics for the resistor only show resistors, no fuse.

I went out to see a Ford resistor tonight to see what you were talking about.
I didn't find a temp on it, but I did find a marking for 1.3 ohms.
hmmm.

Personally, when you start getting into what stuff is called, that wastes my time. Regardless of what it is, it is not a serviceable item. For a $15 item for the resistor, you spend far more time messing around with trying to solder something in there to make it work.
Don't be so cheap, if the resistor is bad, replace it with an OEM part and go on.

delivereguy · April 2003

I hear you, stop wasting my time and just replace the whole part... called dealer parts and the gentleman quoted me $8. Have been a little busy, but will try to get this part and hopefully fix this, before it gets to hot here in Atlanta,ga..
Thanks for your help....

)

przeho · April 2003

I finally had a chance to work on my 94 Escort wagon and many thanks to all who said check the diode in the resistor. My diode was bad, showed no multimeter movement. After checking the auto parts stores and having no luck, I went to a junkyard and got a resistor for a couple bucks. I installed it and now I have a fan that works. Thanks again for all the info and help.
Paul

swschrad · April 2003

if that diode wasn't something like a 3 amp 200 or 400 volt unit, in there just to keep inductive kickback out of the electronic control stuff from the motor. but without the wiring manual, don't know the JEDEC part number to confirm that.

bad things would happen if the diode was installed backwards, so replacing the resistor assembly as one piece makes the most sense.

opera_house_wk · April 2003

It is understandable that this component may be confused with a diode since it is similar in size and shape. A diode in this application has no purpose. The resistors are placed in the exhaust stream of the blower to provide heat dissipation. A permanent magnet DC motor is proportional in speed to the input voltage. At a mid speed, the resistor could drop the voltage 6 volts and dissipate 40 watts. If the motor shorts and there is no airflow, this resistor will get hot. But, the resistor now has 12 volts across it. For a fixed resistance the power increases with the square of the voltage change. This resistor is now dissipating 160 watts and the current is still not sufficient to blow the motor fuse. When plenum boxes were made of metal, this heat wasn't a problem. So when the boxes changed to plastic, some designs needed this thermal safety device in the circuit.

Installing a diode in place of this device will make the blower work as long it is installed in the direction that allows conduction. As I said before, even a jumper wire will work. The motor will run slightly slower as a result of the 0.6V drop of the diode. Look and see if the device in question looks like this:

http://www.radioshack.com/searchsku.asp?find=270-1320

Been trying to find my 1st gen Haynes Explorer manual which I remember indicating this part. You don't get detail often on unit replacement items. Depending on heater design, this may not be needed for fire protection. You said you have seen this two lead device that looks like a diode. I've replaced a number of these in small appliences and they work for years afterwards. This leads me to believe that some of them fatigue or go bad for some reason as they age.

0patience · April 2003

Regardless, if you test it as a diode, it will show if it is bad.
An $8 item isn't worth even attempting to solder a 75 cent item in it.
You say creek, I say crick.

swschrad · April 2003

I briefly thought of going outside, pulling mine, and testing the components to see what I had.

and then I thought, why screw up a beautiful afternoon?

ain't even worth settling my curiousity over. it's eight bucks. pay the man and be done with it.

delivereguy · April 2003

OK,OK,...It's fixed!!! $8!....Sometimes we get a little to worked up over a problem when the simple solution is to just replace the part if it is not to expensive, as was the case here. Sorry to get some of you going there, but some of the theory of the operation of the circuit is not all bad... especially when one is trying to fix it, it is almost interesting....diode,resistor, whatever? it was bad! It can be a problem though when one is frezzing in the morning and sweating in the afternoon, but can now laugh a little. Let there be air!! ....thanks for the help.

)

opera_house_wk · April 2003

And the blower resistor block has a fuse symbol that is titled "thermal limiter" along with three resistors.

Opatience:
"Ford has a thermal fuse
Well, not really a fuse.
There are 3 coils, each provides a certain amount of resistance and there is a diode in the circuit"

Just goes to show you are young enough to learn something.

0patience · April 2003

I've never said I couldn't learn something new.

Although, I have to deal with engineers all day long, if you tell them that a fire engine is red, they will argue that it isn't really red, just how the light refracts to you.

I don't wat to grow up, I have too much fun being a little kid. LOL!

swschrad · April 2003

anybody ever see one before? well, anyway, we're protected now. thanks, operahouse. my curiosity is slated now

zamman · May 2003

I enjoyed reading all these entries, they make a lot of sense. My problem is slightly related to this. When I used the blower for heat or AC, ice builds up on the bottom of the motor, and we no longer have any air movement. Is this the same problem?
Please someone help me. I have a 97 Escort. email at "tkenney@mn.rr.com" thanks.

swschrad · May 2003

one, the drain is plugged in the evaporator housing, this alas appears to be rather common.

two, have a two-gauge check made on the a/c, I strongly suspect the charge level is wrong or you have a sticking relief valve that is causing overcooling.

zamman · May 2003

Would this also cause the problem with the heater?

swschrad · May 2003

so yeah, if you plug the evaporator up with ice and there's enough of it to also cool the motor case down to where it condenses water and ices up, there's probably enough to seize up a damper door someplace. if there's ice and the heat doesn't work, I'd absolutely suspect issues in the evap housing, and both a plugged drain and a charge or vapor regulation issue is not out of the question.

it could be a little icy drool down the housing freezing the blower cage, or it could be sticking a damper, but I'd attack the icing problem first and see what others remain afterwards. it is not good design practice to make a/c that ices up the blower, you are wasting energy and spending a couple bucks too much on the a/c when you build it. if you think like a nickel-shaving engineering department when you look at something, it leads to some trouble-shooting clues.

I may be assuming too much to assume the blower motor has already been tested and found working... blower motor dead so no air flows would also help explain everything, but it still shouldn't ice up that bad, suggesting there is another issue in the a/c. obviously, if the blower is dead, that needs to be attacked first to help isolate and determine how big the other issue is.

opera_house_wk · May 2003

even if the exchanger ices over. Usually the high speed works even if the resistor pack is bad.

zamman · May 2003

I can hear the blower, but no air flow is found. The whole system has been taken apart to see if the dampers are stuck, but nothing was found. If the evaporator is not working properly, then I can understand why the dampers stick.

swschrad · May 2003

when the a/c is dampered into effect, all or most of the airflow is pulled through the evaporator. if it's iced solid and you can't get air through, no airflow. if there's a bunch of slop like leaves and elm seeds and cottonwood cotton in there, you're not only restricting airflow, you also have increased the tendecy for the evap to ice up, because you can't get the water to drip off before it freezes in place. plugged evap and excess cooling look the same until you take the cover apart and see the coil itself.

this is why I am really hard to live with over the fact that they do NOT have a cleanable filter ahead of the coils. I have had to take a system completely apart to deal with it once, and that should not be necessary.

cchad · May 2003

0patience, can you please send me the picture you linked too. It doesnt open. My girlfriends car has the same problems and If the picture explains it maybe me with my little mechanical ability will be able to fix it!!! Thanks for any help!!!

0patience · May 2003

New URL of image.
We had to split the site into 2 different domains, so some images were moved.

cchad · June 2003

Thank You 0patience

A/C, Heater blower fan doesn't work

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