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Old 02-23-2020, 05:55 PM   #1
RKS.PA
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Question Replacing 6 volt heater motor

The original 4 wire heater motor on my '47 Super Deluxe has given up the fight! I've been unsuccessful in finding a replacement from our great sources here on the Barn and on E-bay.

So, I have a 6 volt Unimotor from C&G that is reversible. As was noted here in another recent post, the original motor turned CW for heat and CCW for defrost, controlled by the original heater switch. The original switch has four terminals, one for power from the ignition, and three others to accept 3 of the 4 wires from the original motor....the forth heater wire went to ground.

Is is possible to wire this new Unimotor such that it can run forward or reverse to duplicate the original fan directions?

I'd like to keep the original switch if possible. I've been unable to find anything on line in either a video or wiring diagram to help me along.

Any ideas??
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Old 02-23-2020, 10:05 PM   #2
meric42
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Default Re: Replacing 6 volt heater motor

The original 4 wire motor used the switch to change the polarity of the field winding (relative to the armature) to reverse the motor rotation. I'd need to give it some thought and some studying of the switch to work out if the polarity could be changed for the 2 wire operation and having the 2 speed function as a part of the switch (via a resistor coil in the switch) complicates things too
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Last edited by meric42; 02-24-2020 at 08:34 PM.
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Old 02-24-2020, 06:08 AM   #3
moonraker
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Default Re: Replacing 6 volt heater motor

I did exactly this on my '39 Deluxe. Got some 6 v motor from Napa and connected it to a factory switch. Unfortunately I didn't document it since I thought the task is a-brainer.
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Old 02-24-2020, 08:23 AM   #4
koates
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Default Re: Replacing 6 volt heater motor

Your new heater motor will not work as the original one does with its multi position switch. Why not repair the original motor as they do come apart. I have repaired a couple of these in the past. The only thing preventing its repair is if it is totally burnt out. Find an old auto electrician or an electric motor shop to at least have a look at it. Regards, Kevin.
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Old 02-24-2020, 09:58 AM   #5
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Default Re: Replacing 6 volt heater motor

Kevin is on the right track here. Many times these motors can be repaired if you can find an electric motor repair shop in your area.
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Old 02-24-2020, 07:26 PM   #6
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Default Re: Replacing 6 volt heater motor

I believe FB member "flathead48" repairs heater motors.
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Old 02-24-2020, 08:30 PM   #7
meric42
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Default Re: Replacing 6 volt heater motor

I did a little research and whilst I have yet to confirm my thoughts, here is what I think should work for a two wire installation. If I get a chance I'll check it out in the next week or so.

Attached is a drawing of the switch.
1. Connect Yellow terminal to chassis/ground
2. Connect the two heater wires to Red and Brown terminals
3. Connect the Black terminal to the ignition switch accessory terminal

This should now give forward and reverse function for the heater motor, bearing in mind the two heater motor wired might need to be swapped so that the rotation direction matches the selected position on the switch.

Thinking about it more as i write, as the field coils in the motor are not now switched relative to the armature in the two wire version, the motor might now only rotate in one direction, regardless of polarity. Also the '41 - '48 heater switch is NOT labelled 'Heat' and 'Defrost' - but it IS labelled 'Direct' and 'Indirect' with a cable operated butterfly for the Defrost option. Therefore I suggest that the direction of the motor rotation may only have a minor effect on the defrost function - watch this space as I am now motivated to check this out hopefully tonight.
Attached Images
File Type: jpg 41 - 48 switch.jpg (13.1 KB, 14 views)
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Last edited by meric42; 02-24-2020 at 08:32 PM. Reason: grammar
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Old 02-25-2020, 09:04 AM   #8
RKS.PA
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Default Re: Replacing 6 volt heater motor

meric42, thank you very much. That diagram is exactly my switch and your explanation is very helpful. Yes, I am able to get heat to the windshield with the cable operated butterfly. Closing the heater doors helps this process.
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Old 02-26-2020, 08:23 PM   #9
meric42
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Default Re: Replacing 6 volt heater motor

Checked the theory last night and the two wire motors will only run in one direction regardless of polarity an the one I have in a restored '41 heater that I bought in Oklahoma in 1996 only runs backward... oh darn
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Old 02-27-2020, 03:34 AM   #10
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Default Re: Replacing 6 volt heater motor

Quote:
Originally Posted by meric42 View Post
Checked the theory last night and the two wire motors will only run in one direction regardless of polarity an the one I have in a restored '41 heater that I bought in Oklahoma in 1996 only runs backward... oh darn
Reverse field or armature polarity inside motor and it will run the other direction.

Easiest reversible DC motor is a permanent magnet one...then you just reverse input polarity for CW/CCW.

For a fieldcoil motor you need to reverse polarity for field or armatature...but not both...
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