The Stovebolt Site Forums The Shop Area The Electrical Bay Are the heater/defroster motors 6 volt or 12 volt?

I have a '50s era GMC hot water heater. The heater and the defroster motors both work on 6V and 12V. Yes, the motors run faster on 12V. No voltage markings on the motors. Don't want to burn up a possible 6V using 12V power source.
GM changed from 6V to 12V in the mid '50's.
How do I tell what the correct voltage is on these fan motors?
Jerry

I am just guessing but I don't think you would get a reasonable effort from a 12 volt motor on six volts.

Yes... on 6V the motors do run appreciably slower but i do not know what
a 6V motor"s RPM's are supposed to be. On 6V the fans do put out a fairly
reasonable amount of breeze. Nothing like the 12V though.
The question remains.... what's too slow and what's too fast.
If they are 6V and I run them on 12V till they burn up, what good is that?

Would the use of a multi-meter do me any good?
If so, how?
Thanks,
JB

Even if it is a 6v motor, you should be able to run it on 12v with no issues. I had a 50 DeSoto that I did that with and never had any issues. Ran it that way for years. Going the other way though, you would not get much air movement!

You will get mixed messages on running a 6v on 12 volts. Mine is a 54 and in 54 they still used a 6v system. The previous owner converted to 12v and it very quickly burned up the 6v motor. I had to replace it with a 12v motor $30 from AutoZone. There is no way with a volt/ohm meter to tell what your motor is. A volt/ohm meter will only tell you what you are sending to it.


Linkt to AutoZone heater motor

If you pull the heater and can get access to the motor model number you can tell what it is. I was suprized I was able to find information on my motor on Google by typing in the manufacture information and model number from the motor.

If you decide to switch the motor with the one from AutoZone it is a straight out swap except for the fan. The motor is a 1/2 inch deeper but fits perfect using the same mounting holes and screws. In order to use the original fan I simply took a 1/4 drill bit and ran it through the shaft hole of the fan to increase the hole to the correct size. Once I did that, everything went back together like it was made for it. The motor is reversible. All you have to do is reverse the ground and hot wire to have the motor spin in the opposite direction. You will need to figure out which way you need it to spin after you get it in there.

EDIT: found numbers on the heater motors, see my most recent post this a.m.

There are no numbers on either motor. So... rather than risk the chance of smoke, fire and worse, I just think I'll get two new 12V motors and be done with it.
Thanks for all the info......
Jerry

Motor(s)? It should be one motor unless you have something different than the common Harrison Heaters. If yours is not a Harrison, I am not sure if the motor I linked to is the correct motor(s) for you. During at least through 55 first series heaters where a dealer option, not from the factory. Most were one of two models. Harrison re-circulating or Harrison Fresh Air. Mine is a Harrison re-circulating model but the Fresh Air model are very similar, they just have extra housing that extends over to the side to pull in fresh air. There should be a diverter that flips from Heat to Defrost.

Here is a photo of my heater:


Harrison recircultaing heater

Dave:
My heater has two fan motors. One with a fan blade to move air through the heater radiator and another in an attachment for the defroster on top of the heater shell. It has a small squirrel cage fan in that. The emblem on the heater says:
"Special GMC Heater".
It is not a fresh air heater.
Three rectangular outlet doors on front. Two knobs per door. Knobs are identical
to the knobs on the ashtray in my '51 Chev panel.
Thanks,
Jerry

There are two different 12v motors readily available today, I can search and repost but I recently covered heater motors in a different thread.
Should be one that fits without drilling out the fan.

I'm presently running a 12V replacement motor from NAPA in my GMC with 6V. It runs fine, as if on medium or slow all the time. Later I'll upgrade the truck to 12V, that's why I put the "wrong" motor in.

Grigg:
I will check out your thread on heater motors.

Thks,
Jerry

UPDATE !!!

I scratched around on the ends of the heater motors and found numbers.

Larger motor with fan blade: Delco 47472
Smaller defroster motor with squirrel cage: 47631. (no name)

6V or 12V. ??

Jerry

On my 55 Gmc, it still has the stock heater motor which was 6V at the time. The truck has since been converted to 12V. With 12V, the motor would operate a lot faster than with 6V. For fear of having it burned out, my dad some time ago installed a resistor(resembling a ballast resistor)in series with the motor. It has run just fine whenever its turned on.

AL

Typically a 6V motor will have heavier gauge windings, but probably not enough so to tell difference easily. Part numbers will help if you can find reference to them. Coil resistance can also help, but need to have precise multi meter and again have reference material to tell which is which.
My 6v motor in my 52 had to be repaired , probably due to using it when truck was converted to 12v for prolonged times.
Using it now (12v) through a ballast resistor, it runs pretty quiet and blows moderately. If direct (no resistor) its giving a decent hum and blows fairly hard.
Hope this helps. Not sure if I have part number from mine somewhere. Don't remember seeing one when I had it out, but I'll check.

I have tried researching the Delco motors on the internet with no luck.
Those numbers now show up as some kind of starter part.

I was hoping one of our Bolters had part number references for the
motor numbers that I posted previously above.

Jerry

If you could measure the current draw of these motors at both voltages you may determine if they are 6 or 12 volt motors. I've checked the current draw of my 6 volt fan motor simply with the indicator of my switchable 6/12V battery charger.

As a rule of thumb (no need for scientific precision) doubling the voltage will result in twice the current and gives 4 times the power. Half the voltage will result in half the current and hence one quarter of the power. Power (Watts) is roughly calculated by voltage (Volts) times current draw (Amps).

Any excessivly high or low power number will indicate a wrong voltage. It is of course a bit difficult to determine which values might be reasonable and what is too high/low in regard to them. But if you get a good airflow with about 30-40 watts, then 100 watts will be quite obvious way too much.

My 6 volt motor was going (the term running just didn't apply then) with 8 amps when I took it off the truck. After cleaning and greasing it was running with less than 5 amps. This would give power values of 48 watts before cleaning and about 30 Watts after cleaning/greasing. (All readings with the fan cage as load).

I accidently applied 12 volts one time (cat had tapped the switch) and it read over 8 amps, hence 12V times 8.x amps resulting in about or over 100 watts, more than 3 times the power it was rated for. The stronger air flow in my opinion didn't justify this raise in power.

I am sure it would not have kept up with this abuse for a long time. There are two main problems which will over time lead to failure:
- The first one is that the windings will at some time overheat and burn off the insulation and thus short out the windings.
- The second may be the excessive current flow which will provoke more sparking at the brushes and the commutator which will in the long run damage the commutator and lead to excessive brush wear.

Checked through all my pics and that was one of the few parts I didn't take a picture of. The repair I mentioned was almost all solder of rotor coil melted off commutator sections, I expect from excessive 12v use. 6v motor can handle 12v, but tends to overspeed which creates more friction which requires more current which creates more heat as well as the friction itself.