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#595097 Tue Nov 24 2009 04:34 AM
Joined: Jul 2007
Posts: 293
Wrench Fetcher
The motor in my '49 fresh-air heater has been wired up and working for several months. Yesterday, I connected the hoses to the radiator and decided to go for a test drive. Some warm air in the cab would feel nice this time of year.

I had been driving for about 10 minutes, with the heater on, when all of a sudden - BANG! I heard a loud firecracker-type explosion and saw a puff of smoke from the heater. My life flashed before my eyes because I was not only driving, but afraid my 3-year project was about to burn to the ground.

I turned the heater off and managed to pull over and stop. Fortunately, no fire. After my heart rate dropped below 100, and I looked more closely, I noticed that the voltage reducer on the heater had essentially exploded. It was in several small pieces inside the cab.

The truck is 12-volt, and the voltage reducer was supposed to drop the voltage from 12-volts to 6-volts for the old motor. The voltage reducer was brand new from a favorite vendor.

What caused this?? Anybody else have this problem? Did the voltage reducer overheat? I had assumed the old motor was 6-volt, but there are no markings on it anywhere. How do I confirm that it's a 6-volt motor? All is good, now, but that was definitely a scary moment.

Joined: May 2006
Posts: 8,490
Master Gabster
Sounds like something shorted to ground. Might need to check that motor out to make sure there isn't some sort of internal issue.

Bill Burmeister
LONGBOX55 #595165 Tue Nov 24 2009 12:48 PM
Joined: Mar 2002
Posts: 9,171
They sell a resistor that is in a ribbed metal case and has a mounting hole at each end. It is usually described as "heavy duty". It is around 1 ohm in value. These can be used for an original radio or a heater. One of our members bought one for his AD radio and it blew up just like yours. The second one, a replacement, was OK.

Joined: Jul 2007
Posts: 293
Wrench Fetcher
Yep, that's exactly what I had. Ribbed metal case, gold color, mounting holes at each end, described as heavy duty and made for heaters. The cost was $18.25.

Not to switch topics here, but I see that a whole new 12-volt motor is only $49.95, and most of the vendors sell them. Has anybody successfully swapped their motor recently? Any problems? Where did you buy the motor?

Joined: Jul 2001
Posts: 3,904
Master Gabster
easy fix - take your old motor to a local parts store and match details [shaft size, rotation and rpm] in 12V


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squeeze #595235 Tue Nov 24 2009 05:44 PM
Joined: Dec 2005
Posts: 2,607
Truckernix,That was me it happened to.I was bench testing an AD radio and the reducer popped like a firecracker,thought i fried the radio.I took it back and exchanged it for another one,everything was fine.

I installed a 12 volt heater motor that Jim Carter sells.You have to drill re-drill a couple of holes to mount it center.I think i had to make a new rubber gasket at the firewall.The new motor was smaller in diameter.

If you decide to get another reducer,make sure you have it mounted flush to the dash panel.The dash metal will act as a heat sink for the reducer,keeping it cooler.Be sure no electrical wiring is close to the reducer,it will melt it.

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bowtietim #595246 Tue Nov 24 2009 06:40 PM
Joined: Aug 2005
Posts: 9,517
Ex Hall Monitor
OR you could do like I did on my 55.1 panel and just run it on 12v. I never had an issue with the motor running on 12 for over 100K after I converted it to 12v.

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Tiny #595261 Tue Nov 24 2009 07:35 PM
Joined: Feb 2008
Posts: 14
Wrench Fetcher
We have had nothin' but problems with voltage reducers on heaters for years now.
Because they get hot & want to melt & burn everything around them { not to mention explode }....We don't mess with them anymore...
We install new 12 volt motors in them but, it is tough finding an exact replacement motor that has the same overall dimensions with the correct keyway pad for the blower cage set screw.
We got lucky & found replacement 12 motors at an electrical supply store that was going out of business a few years ago & we stocked up.

Joined: Jul 2007
Posts: 293
Wrench Fetcher
I disconnected the voltage reducer and tried running the 6-volt motor on 12-volts. The motor runs fine, but the heater switch located left of the steering column literally turned red hot and started smoking. The switch always gets very hot, which I understand is normal, but apparently the additional heat that cause the voltage reducer to explode was now being dissipated through the switch. I quickly decided this was not a workable solution and shut her down.

So, my options are to install a new voltage reducer or swap the 6-volt motor to a 12-volt motor. I was leaning toward replacing the voltage reducer, because I found an on-line store that sells them for half the price, and installation would be much easier than replacing the motor. However, the heat at the switch got me to thinking about which option would be best for my switch. If I install a 12-volt motor, will the heater switch run cooler, or would the switch run the same temperature as a 6-volt motor with a new voltage reducer?? I'm thinking the 12-volt motor runs at half the amperage as the 6-volt motor, so maybe my switch gets half as hot. Any thoughts on this?

Joined: Jun 2009
Posts: 2,269
Shop Shark
Replacing the motor is not that hard if your heater is like my fresh air unit. Probably be cheaper in the long run too.

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