1941 Under Dash Heater Wiring with New Blower Motor

[J. Russo]

I'm inquiring to see if anyone has experience with installing a modern 6 volt blower motor into the under dash heaters used in pre-1941 and 1941 Cadillacs.

I purchased a 6 volt blower motor from Chevys of the 40s that fits these heaters. It has 2 wires compared to the 4 wires of the original blower motor. I wired this new motor to an on-off-on toggle switch and it reverses direction great. I would prefer to wire it to the original switch.

I currently have 3 of these heaters.

I included a link to the new motor, photos of the original switch, original wiring diagram and the type heaters I am referring to.

I'd appreciate any advice anyone might provide.

Thank you

https://www.chevsofthe40s.com/detail/5952/Chevrolet_Heater_Motor_6Volt.html

[39LaSalleDriver]

Following this with interest as I just recently had my heater core rebuilt with hopes of reinstalling it soon. The motor that came with mine also has a two wire arrangement. I know it runs, but I haven't checked to see if it reverses. Been wondering if it can be wired so that it blows/stops/reverses as it should, but only at one speed which would be okay by me. Forgive my ignorance, but electrical stuff just confounds me every time.

[J. Russo]

Jon,

Is your blower motor new or is it original?

This is the reversible toggle switch I purchased from NAPA:

https://www.napaonline.com/en/p/GRO822122?impressionRank=1

There are different ways to wire the toggle switch. Keep in mind you only get 1 speed in both directions with this switch.

https://www.youtube.com/watch?v=u0Lm3P1U7UQ

https://www.youtube.com/watch?v=il571D0XXjY

[Tom Boehm]

http://www.secondchancegarage.com/public/703.cfm

Here is a link to a story about repairing this motor and switch. It may or may not be helpful. I am not good with electric. I was just lucky on mine in that I found the correct motor and correct switch and I stretched my electric abilities to the limit to follow the wiring diagram you posted to make it work.

[bcroe]

If your replacement motor has only 2 wires, but can be reversed by
swapping the wires, it has a permanent magnet field.  Simply wire it
to the switch at the point where the original motor 2 brush wires
were connected.  Note the original motor had the field winding with
one lead grounded, the other lead was simply turned on and off by
the switch.  That winding simply disappears with the permanent
magnets, the brush wires connect as before. 

If the replacement motor has a different current draw, the value of
the speed resistors might need adjustment.  Bruce Roe

[J. Russo]

Thank you to all for your input.

I was able to figure out the wiring for this new blower motor with the original switch. For anyone interested, refer to the blower motor link and the diagram above where the letter markings are on each post on the switch.

The new blower motor has 2 wires (black and orange). I attached Orange to "C" and Black to "B". You can swap these depending on the direction your fan is blowing once connected, to make sure it is blowing heat or defrost.

I connected "A", which has an inline 15 amp fuse to the battery pack. On the car, this wire would be connected to the ignition switch.

I connected "D" to The negative wire on the battery pack. I'm making an assumption here that this wire would be grounded to the dash when installed in the car. Looking for input on this one.

The fan works just like the old blower motors with the original switch. It reverses direction and has adjustable speeds. The resistors do get hot when running the fan at lower speeds, but I am told that is normal.

I had this motor running for about 20 minutes on high speed and the wires, fan and switch did not over heat.

As an FYI, I was also told that the motor shaft may need to be cut so that it does not interfere with the heater core. I haven't confirmed that yet.

[39LaSalleDriver]

Apologies for not getting back to this earlier, but I've finally started redoing my upholstery and I'm doing it all myself. I've been replicating all the burlap spring pockets in the back seat which were water and critter damaged so you can imagine my hands have been full. But I digress...

I presume the blower motor I have is a replacement, but of unknown make or vintage. I say that because it only has two wires, a black one and an orange one. Also, I pulled out the squirrel cage a partial tag of some sort (safety or something like that, no maker or model) about three years ago which was of a more decidedly modern date. Nonetheless, it fits into the case the way it's supposed to from what I can tell.

I dug it out today and attached it to a battery and discovered that it runs fine, and if the wires are switched, the motor runs in reverse, so that's good. Looks like I should be able to hook it up to my original switch like you did and make it work as it should. Thanks for the photos and instructions, I'll definitely be following your lead.

Brings me to the question though, is there some sort of resistor built into the switch which allows for different speeds?

P.S. Glad to see my redrafting of the wiring schematic is being put to good use. The old hand drawn version from the authenticity manual and online was driving me nuts, so I made a new one quite some time back. 

[J. Russo]

To answer your question about switch resistors, please see photo of the original switch. I circled both resistors.

[39LaSalleDriver]

To answer your question about switch resistors, please see photo of the original switch. I circled both resistors.

Fair enough. I didn't realize that's what those were. All I knew was I needed to be extra, super careful when I cleaned up my switch to not break those coils! 

[Tom Boehm]

Thank you Jon for cleaning up the wiring diagram. You should submit that to Bill Anderson to include in future copies of the Authenticity Manual. John Russo's info about wiring the motor should be included also.

[bcroe]

The new blower motor has 2 wires (black and orange). I attached Orange to "C" and Black to "B". You can swap these depending on the direction your fan is blowing once connected, to make sure it is blowing heat or defrost.

I connected "D" to The negative wire on the battery pack. I'm making an assumption here that this wire would be grounded to the dash when installed in the car. Looking for input on this one.

Yes, I forgot that one point. My description was for a shunt connected
(field and brushes) motor.  Hard to tell from here, but for a series
connected motor, the return to ground would be through D, the field,
to ground.  With a permanent magnet field (no field winding) terminal
D should be connected directly to ground to complete the circuit, as you
said.  Bruce Roe

[J. Russo]

This is great information for me as I have 3 heaters and all 3 blower motors need replaced, mainly because if they stop in the wrong spot, I have to spin the fan to get them started again. From what I've read that is a commutator issue within the motor.

I only have 1 original switch. The switch is very hard to find.

[39LaSalleDriver]

Thank you Jon for cleaning up the wiring diagram. You should submit that to Bill Anderson to include in future copies of the Authenticity Manual. John Russo's info about wiring the motor should be included also.

If there are future editions, I would be delighted if they wanted to add that diagram. I'm not even interested in credit for it since I really didn't do anything other than redraw what was already there. As a side note there's quite a few things I would like to see added/updated/changed in the Authenticity Manual regarding topics I have found to be incomplete or in some cases erroneous. Perhaps my biggest criticism is that it appears the author(s) or contributors were more focused on convertibles than sedans and coupes when they put it together, but that's not a crusade I'm interested in taking on. In fact, I've got my hands way too full with another book project that has nothing to do with cars to even consider getting involved in another.

[Tom Boehm]

Hello Jon, What are the errors you noticed in the authenticity manual?

[39LaSalleDriver]

I likely worded that poorly. Errors of omission would probably be more accurate. By no means do I mean any disrespect to the authors or anything like that, but there's some degree of information I would have thought would have been in there that wasn't included. Examples I can think of off the top of my head are trunk hinges, and sun visor brackets. Items which I've had to dig extensively into to find the proper patterns because the ones on my car had been replaced and it took me a long time to even figure out that they were the wrong ones. Fortunately, this forum can be a treasure trove of information for those willing to dig around a bit. I also have to be mindful that the Authenticity Manuals are designed to assist in judged competitions and the like more than being a restoration guide so many things may have been omitted because it was presumed that certain things were common knowledge.

[Tom Boehm]

One thing I noticed was the manual does not account for all the variations of runningboards in the models covered.

[Brad Ipsen CLC #737]

But they got done.  It takes a lot of time to put all of this together, pictures, writing, layout, etc.  Another thing is the "where to buy and what to buy for parts" is getting obsolete.  This was put out almost 15 years ago now and much of the info goes back much further than that.  The message board is the way to go for further details.  The engineer's instructions to the factory floor are 3/4" thick.  I assume you have your answer on the visor hinges but that would have been a perfect question for the message board.  3 different types in 39-40.  60S has the Fleetwood type, convertibles are completely different and then the standard version which just to keep the parts guys confused Cadillac changed the screw spacing in 41.

[Ohjai]

Brad I was not able to locate the Message Board.  Is this forum what you are referring to?


Thanks,


Jim

[Brad Ipsen CLC #737]

Yes

[J. Russo]

Update: I installed the new blower motor in my ventilating defrosting heater today. I did have to cut about a half inch off the fan blade shaft so that it did not interfere with the heater core. I recommend installing the fan blade first to mark where to start your cut. That will insure you don't cut too much off. There are also two threaded screws protruding from the front of the motor that I had to cut.

It works great and is very quiet.