motor in gas heater won't shut off

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  #1  
Old 03-11-06, 05:34 PM
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motor in gas heater won't shut off

I already posted this in the "gas heaters" forum, but I wanted to post it here too, 'cause you guys are really smart.

My house is 1953. I have an old "Commonwealth Force-Flo" natural gas heater, mounted in the wall. Model K-50 DWH, or, K-57 DWH. It's almost 6 feet tall. There's a motor in the bottom of it that forces out the heated air. The motor hasn't worked since I moved in two years ago. I just took off the juction box cover on the motor and saw that a wire splice had come undone, so I hooked it back together. The motor now works, but it doesn't shut off. The wiring in the junction box is as follows: hot wire from source (main breaker box) comes into box and is spliced to a wire that runs up somewhere into the upper portion of the heater. A wire from up in the heater then returns down into the junction box and is spliced to a wire that goes to the motor. The return wire from the motor comes back into the junction box and splices with the neutral wire that returns to the source (main breaker panel).

I'm wondering, is there some kind of thermostat(or something) up in the heater, that opens and closes, depending on the heat of the air, thus completing the electrical circuit when it wants the motor to run, forcing air out into the rooms of the house? If so, is my motor continuously running because, perhaps, the thermostat inside the heater is damaged, and will not break the circuit, letting the motor shut off until it is needed again?

I may be way off base, but I'm worried about the motor running ALL the time. That doesn't seem right. I need to do something to remedy that situation. Thanks in advance!!
 
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Old 03-11-06, 06:00 PM
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Yes ther is usualy a t-stat type device in the plenum, you are correct.
I have seen these go bad. The device is about 3x4 in.big, if you take the cover off of this device you will see a dial with temp settings. Most likely this has failed, not uncommon.
this operates in conjunction with the heat plates. QUICK/Short ex. gas comes on furnace gets up to temp this device heats up and turns the fan on, thermastat is satisfied the gas shuts off and the fan runs untill temp drops and this device opens the fan ckt.
To replace disconnect power and note the wire config. remove this device and you will see a probe on it, match the model# and the probe length, available usualy at a heating supply not the big box.
 
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Old 03-11-06, 08:31 PM
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lectriclee,
sure enough, I took it apart and found a device, (a disc), & on the back
of it was printed, "Therm-o-disc." I'll take it by the local supply store Monday. Thanks for your help!!!
 
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Old 03-11-06, 10:33 PM
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Diagnostic information was insufficient to incriminate the limit switch.

I would rule out a lot of other possibilities before I started replacing parts.
 
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Old 03-12-06, 06:23 AM
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Bolide, your right, I should have asked if the t-stat controling the gas gun was operating correctly,Ie: gas on and off with apro. temp.. However in the last 2-months I have had this problem
with 4 different clients, on both gas and oil units. Were will stated that the fan had not worked for 2 yrs and he found the motor disconnected, I found this the LOGICAL place to start.
 
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Old 03-12-06, 07:02 AM
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Hey guys,
The motor runs well when hooked up to power, and the thermostat has always worked well. What else could it be? The very small "Therm-o-disc" that I took out seems to be the logical problem. Assuming they still have a part like this available, it doesn't look like it will cost much at all. Maybe they even make one that's the same size and shape, and technologically much more upgraded. 'Course, I'm guessing at all this. Don't forget, I only drive a truck for a living, and sometimes we "truckies" are pretty dense.
 
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Old 03-12-06, 07:15 AM
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When you find one , READ the instructions carefully for the temp settings, Typicaly they are
100, 150 & 180/190 deg. F- .... ON-OFF-High temp. respectivly.
 
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Old 03-12-06, 07:19 AM
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sorry, it should be , OFF-ON- High limit
 
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Old 03-12-06, 07:22 AM
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lee,
this one doesn't have anything on it that you can adjust, or set. It is just a disc. On the back, it has different numbers engraved. They are: 11T-12, .......23225, .....12-61, .....and the last one is, F-140. I'm guessing, from what you said, that perhaps this "F-140" might be the temperature rating. Any thoughts?
 
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Old 03-12-06, 07:41 AM
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Now I'm aproaching the limits, Best to take this from here to the supplier/heating experts, they will know much better than I. I just tried to get you in the general direction. Good luck.
 
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