Mopar Heater Question

[KenaiGary]

I've searched these archives, Joe's forum and the T137 site for info I need, but can't find anything so am looking for assistance.

Started my 61 WM300 today after it has been sitting in the Alaska cold for a few weeks. It started fine and I pulled the heater switch out to full and it worked. Once the idle smoothed out, I got out of the truck and started clearing the snow. After about 10 minutes, I got back in the truck and the blower was not working. I checked the switch and have power from the switch to the heater.

Before I start pulling the heater off, I was wondering if anyone had an exploded view of the Mopar heater I have. On the face of the heater it shows "Mopar 1922657" but in my parts books I can't find that number. They have heater parts numbers that start out as "1922_ _ _" but the remaining numbers don't match mine.

From what I've been able to find on the forums, I have a Model 75 as it is supposed to be the original heater that was rebuilt just prior to me buying the truck in August. I now question that...maybe it was just painted...

Any help is appreciated. I'm supposed to be in a Christmas parade on Nov. 25 and without heat and a defroster at -20, I need to figure this out or cancel. Thanks

[Frank Irons]

Verify the ground of the heater motor to the housing and the housing to the chassis. By tightening a few nuts or bolts you could be working again.

Frank

[oldmopar]

Here are 2 diagrams 1st is a 75 heater 2nd a 77.

[KenaiGary]

Mopar Heater

Thanks, guys. I'll be checking the grounds after I go move around 10" of snow we got last night.

What service manual did the diagrams come from? I didn't find these in the ones I have.

[oldmopar]

Thanks, guys. I'll be checking the grounds after I go move around 10" of snow we got last night.

What service manual did the diagrams come from? I didn't find these in the ones I have.

They come from parts manuals not service manuals the 75 heater is from a 1957 manual the 77 heater is from a 1959 manual. The model numbers get higher with the years of the trucks

[KenaiGary]

Mopar Heater

I feel like a fool. I have the WM300 parts manual and there's the heater diagram on p. 3. I flipped through that last night and that page stuck to the front page because of static--mighty dry up here. Still not sure what model mine is because the diagram doesn't state it like the two you sent me, but the one in my parts catalog is the one I have.

Now the good news...I think. Checked the ground from the housing to the firewall and all was good. Before pulling the heater to check the motor ground, I thought I would try what my great uncle told me to try about 45 years ago when an electric motor just stops working. He said to tap the motor housing with a small hammer all the way around it. If I remember right he said sometimes the windings get caught up or sticky in an old motor and this will loosen them up enough to spin and start working again. I've used that method on old alternators and it has worked occasionally.

Today, it worked and my heater is putting out the heat. While it might be a temporary fix, I'm good with it right now. My great uncle was a cantankerous old PA dutchman who had a 160 acre farm outside Phoenixville, PA. He said if the hammer tapping didn't work, you need to get a bigger hammer and then if that didn't work, you need to rebuild the motor.

[DavidGB]

Heater

Typically, when you have to tap an electric motor to get it to run, you have a problem with the brushes. Eventually, and depending on how much you use the heater, the tapping will evolve to a destructive level. While you have the luxury of time, I would look into replacing the brushes.
DavidGB

[KenaiGary]

Mopar Heater

Yes, I plan to pull the heater motor over the holidays and fix it right. Hopefully it will last until then. Thanks for the advice.

[KenaiGary]

Heater Question

I finally found the time to order and install a new blower motor for my heater from VPW. The image shown in the VPW catalog didn't exactly match what I got, but I made it work to a point. My problem is that the fan isn't moving as much air as I think it should and know it isn't sufficient to keep the windshield defrosted since I drove it afterward.

Background: I believe I have a Model 79. It is not a Model 75 or 77 as posted earlier in this string. I've posted the diagram from my S Series Service Manual 1962, but it doesn't indicate the model. In reviewing my other manuals, I believe it is a Model 79, it is not a Model 83. The Model 75 has a fan and blower wheel while the Model 77 has a blower (mouse wheel). Mine just has a fan with set screw.

VPW sent me part #06:HM12V0811, which is the only one they have and it is different than my non-working motor. The part #in the WM300 service manual is: 1922703. The VPW catalog shows two long post terminals that extend into the cab and two short terminals that go into the heater frame, but the one they sent had two long terminals on each end. In order to adapt it to fit I had to cut the terminals that go into the housing or else the fan would not turn as it would bump the terminals. All went well with the install. I have three definite fan speeds, low, med and high, and the fan seems to spin at appropriate rpms at each speed, at least I think they do.

I tried adjusting the fan on the shaft and felt that the more it was inset into the housing, the more vortex it would create. That didn't seem to help so I reset it further out from the housing and that didn't make a difference either.

The Model 75 fan/blower unit looks like it would blow more air but I don't believe it will fit my housing.

Questions I have that I'd appreciate your input:

-Maybe the motor I purchased spins at a lower rpm than what I need?

-Maybe the shaft on the new one is spinning in the wrong direction, but I can check that out once I have some time to pull the unit again, but would appreciate it if anyone knew if this is a possibility.

-If it is turning in the wrong direction, can I reverse the wiring and connect the ground to power and power to ground and the shaft would turn in the opposite direction? One guy told me this, but I am hesitant to try since that seems like it could reverse the polarity and/or burn the motor out. The shaft does spin in either direction.

Also, is there anyone out there that rebuilds these motors? They appear to be sealed units, but there is an indentation that runs around the center that almost appears it might be serviceable. As you can tell, I am definitely not an electric guy, but I was proud I did the install and all seems to work well...but, not enough air blowing, which was the whole point of this exercise. Yes, I checked the air movement at the housing where the hoses attach and little air was coming out, and both hoses are clear with no holes or loose fittings.

The heater core does get very hot and that in itself warmed the cab up in -20 weather, but the defrost was not sufficient due to lack of air moving.

Thanks for any help, guys.

[Matthew Ziegler]

voltage

Is your truck still 6 volt or has it been converted to 12?

[KenaiGary]

Heater

12 volt.

[KenaiGary]

Heater Fan

Finally got this figured out and hope what I learned will help other WM300 owners.

I learned today after some trial and error that my heater fan is supposed to turn counterclockwise. The motor I bought is for a Model 75 and 77, and I have what appears to be a Model 79. The older models had squirrel cage fans and they spin clockwise. So when I originally installed the motor the fan was cutting the air rather than blowing it. Actually it was blowing it, but back toward the heater core.

So I reversed the polarity running the motor ground to the heater power switch and the original power to the ground, which reversed the fan direction. Works like a champ and I can now drive this winter. Bring on the snow!

[KenaiGary]

Heater Fan-VPW

VPW may want to take note of this in their catalog or when they talk to customers wanting to put the motor they carry into a heater that is Model 79 or later. It would save customers many headaches. The motor for the Model 75 and 77 will work in a Model 79, but it takes some adjustments.

[JeffTheMarine]

Is your truck still 6 volt or has it been converted to 12?

I was under the impression that by the time they got to the WM300 models they were all 12 volt from the factory. Correct me if I am wrong but I am pretty sure about that.

Thanks
Jeff

[KenaiGary]

That is my understanding also. My 61 is 12 volt and came that way.