Heater Blower Motor Resistor Repair and Replace

[Wildchild467]

The heater blower motor resistor burned out a little while back in my Deuce. I researched a replacement but did not find anybody that had one. Since wire wound resistors are not usually expensive, I decided to see if Newark had a similar resistor. I found a direct replacement and all I had to do was cut off my old wires on my resistor and solder on my new ones. Attached are pictures of my old resistor and the process I took to solder on the leads from my old resistor. There is also a picture to show why my old resistor failed. There was a chip in it and the wires in the resistor rusted out. The Newark part number is MC14662. The values for the resistor are 5 Ohms and 50 watts. I think this is the same resistor the 800 and 900 series, but I am not sure.
Here is the link to Newark.

http://www.newark.com/multicomp/mc14662/resistor-wirewound-5-ohm-50w-5/dp/28K6276?ost=MC14662

 

[Warthog]

I always love it when someone takes the time to find a replacement part and documents the findings.

Thank you.

Warthog

 

[Wildchild467]

I agree. You're welcome warthog!

 

[todds112]

What was the symptom when it when out? Did the blower motor not run at all?

 

[Wildchild467]

The blower only ran on high speed, not low speed when the resistor was bad.

 

[tcruwithme]

High/Off/Low switch wiring

Ok, I just found the wiring schematic that Doghead posted. It looks like power is supplied from 400 coming from a circuit breaker on the engine side of the firewall. That power goes to the center post on the High/Off/Low heater switch. Then the low output of that switch goes to the resistor. The high output ties into the other end of the resistor and then goes out to the heater motor. Is that all correct?

 

[gungearz]

I had no idea that there was a resistor in the system... this is great info.

The system I have is the coolant heater that I fabricated to fit under my dash... I have the wiring on a 3 pole toggle switch, 12v on one side, 24v on the other, heater in the middle... 12v works as low and 24v as high..

Thanks for the info...

 

[Wildchild467]

Update: My heater quit working on low and I looked under my dash with a flash light and saw the resistor was a little crispy and I suspect that it is the reason my heater fan is not working on low. I don't understand because it is the same Ohm value and watt rating as the original. This could be just a isolated incident with me, but I'm still not sure. Has anybody else out there bought this resistor and had any issues with it?

 

[Wildchild467]

Maybe somebody with more electrical experience can help me with this question: If too much heat was generated with the 5 ohm / 50 watt resistor (same specs as factory), would a 4 ohm /50 Watt resistor generate less heat (since heat was probably the cause of the failure)? I am wondering if i can get the same length resistor so it fits in the same spot as the old one but a little heavier duty. the 4 Ohm will spin the motor a little faster too on low, which might be nice. Anybody have some thoughts/opinions on this?

 

[steelandcanvas]

Sounds like a fluke. Buy another correct value resisitor and try again. Was it securely mounted? Mine has little brackets that mount it to the firewall, that may help dissipate some of the heat the resistor generates.

 

[Wildchild467]

Mine was a direct replacement... mounted just like the original. My motor seems to run just fine so I am not sure what could have made it burn out. I need to actually test it to make sure that is the problem, but it only works on high and the resistor looks crispy. So I am taking a guess that is the problem. All connections are good.

 

[LiqTenEXp]

Well it could be that motor has an issue causing excess current draw to occur. Things like bad bearings/bushings, lack of lubrication, etc could be a cause of excess current. Suggest that you inspect that the motor moves freely and does not bind. Check for obstructions that could be causing drag on the blower.

 

[74M35A2]

Well it could be that motor has an issue causing excess current draw to occur. Things like bad bearings/bushings, lack of lubrication, etc could be a cause of excess current. Suggest that you inspect that the motor moves freely and does not bind. Check for obstructions that could be causing drag on the blower.

Exactly. Best thing to do would be to check current draw on the motor on high to begin with (regardless of what it is rated for labeled as), and go from there to size the resistor correctly. We have high accuracy clamp on DC ammeters at work as you are aware of , bring it up!

From there, obtain a higher wattage rated one, get air flow moving across it (on cars they place it in the HVAC tunnel for this exact reason), or you could use 2 in parallel to lessen the load on each, but calculate the final target resistance you want when doing so before ordering them. Also, is that resistor rated for that dissipation in stagnate air, or is there a minimum airflow requirement for it?

 

[Wildchild467]

Exactly. Best thing to do would be to check current draw on the motor on high to begin with (regardless of what it is rated for labeled as), and go from there to size the resistor correctly. We have high accuracy clamp on DC ammeters at work as you are aware of , bring it up!

From there, obtain a higher wattage rated one, get air flow moving across it (on cars they place it in the HVAC tunnel for this exact reason), or you could use 2 in parallel to lessen the load on each, but calculate the final target resistance you want when doing so before ordering them. Also, is that resistor rated for that dissipation in stagnate air, or is there a minimum airflow requirement for it?

Thanks for your help Jerry. It would be good to know and we could also test the blower motor in your M925A2 which would have been the same motor as mine, but you have the newer Napa replacement. It would be good to figure out. This resistor is just made to disperse heat in stagnate air of the cab, which still wouldn't be that stagnate. I will check my motor to make sure it is turning good and I will check it with an ohm meter too to make sure nothing is shorted. I should add, my heater does have a fuse (which I added) I believe it is either 10 or 7.5 amps. It works fine on High, just not doing so good in low. I would rather over build the system and fix it once... so next resistor I get might be a 100 watt one if we do not find anything wrong with my motor.

 

[Wildchild467]

I wonder how many watt the resistors are in the automotive world...

 

[mhassett]

Excellent research. You solved my problem that has been bugging me.
Many thanks.
MHassett

 

[74M35A2]

I wonder how many watt the resistors are in the automotive world...

1.21 Jigawatts

 

[74M35A2]

I believe low on these blower switches supply 12v to the fan motor. I also believe you have a dedicated 12V system, so if I was you, I would ditch the resistor and source 12V to the low side of the switch and be done with it.

If you want to figure out a correctly sized power resistor, your heater tunnel data plate said 28V @ 6.5 amps, so go from there.

 

[Wildchild467]

Here is the information on the data plate:



So to find the watts of the system, we multiply the volts x amps = watts. so... 28 x 6.5 =182 watts. If it is on the low setting that would be half the voltage, so it would be 91 watts of power. The original spec'ed out resistor that I had before was 50 watts. Unless I am missing something, I think i should have a 100 watt resistor instead of the original 50 watt. Are there any electrical gurus out there that have any input on this?

 

[W8BUH]

We have a M109A3 for our ARES Radio group. The heater resistor went to crap and was wondering if any can help me with getting a replacement part. It is mounted to the under the dash.