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civiccrazy · Nov 17, 2008, 04:32 PM

Coleman Presidential III Model # 7970A856 Furnace

The furnace runs for 1-2 minutes, then shuts off for about 30 seconds to a minute, then comes back on. It does that until it gets to the temp I set the thermostat to. I called the local technician, he said it was the fan Switch. He said check the voltage going to the fan switch. I checked the voltage going to the fan switch. Both wires to ground read 120vac when running. When off, the bottom wire to ground read 120vac and the top wire read 0vac.

So, I don't think it's the fan switch. What else could It be?

Also, tonight the fan motor started squealing really loud. Can I fix that or do anything to it to stop from doing it. Or do I have to replace the motor?

letmetellu · Nov 17, 2008, 07:52 PM

It sounds like all along that the problem was in the motor, it has an internal heat protector and when it would run for 30 seconds and cut off it was the internal switch that was cutting off the motor.

The reason I believe this is because the motor is now squeking, that probably means that the bearings in the motor are either dry or they are worn out. If you knew where to buy a motor it is a job that you can do yourself.

civiccrazy · Nov 17, 2008, 08:17 PM

How sure are you that it is the motor? Not something else too?

hvac1000 · Nov 17, 2008, 11:54 PM

You can try to lubricate the motor if it has lube holes if not sometimes you can put a bit of oil on the shaft where it comes out of the motor. This will kind of lube the front bearing sleve but not the back bearing sleve because it is not accessible unless you tear the motor apart. With the noise it is making the motor is probably shot anyway so eventually you will have to replace it even if the lube helps for awhile. You could have two problems including the blower fan switch out of range and the motor but the motor I would replace first.

Looks like you have also been posting with the same problem over here

http://www.mobilehomerepair.com/phpb...pic.php?t=4066

Robert the moderator is a friend of mine. LOL He also has all the parts you need for your furnace and is more knowledgeable on mobile home furnaces than I am.

letmetellu · Nov 18, 2008, 09:54 AM

I am not sure that it is the motor, I was just giving you another thing to check. If you would like to just oil the motor and if it is a direct drive motor you can pull the blower housing out of the furnace, take the motor out of the housing, this will give you access to both ends of the motor. Then you can drill a very small hole in each end of the motor right by the shaft, (maybe a 1/2 to 1 inch from the shaft). This will let you put oil into the holes and it will wick down to the shaft. Put several drops in each end.

civiccrazy · Nov 18, 2008, 02:08 PM

I had someone come out and look at it today. Two switches were bad... the one that switches it from AC to Heat, and the one on the little box below that which I think is the power switch. I asked him about the motor, and the whole time he was here looking at it with it running is ran fine no sqeaking or anything.

I am thinking about buying a whole new unit next year. THis one is 18 years old. What is the average life span of a furnace?? And what kind should I look for to buy if I do buy one?

hvac1000 · Nov 18, 2008, 05:26 PM

There is no set lifetime for a unit BUT Mobile Homes do have to have a high velocity/static blower to make up for the restricted duct system. They also have to be rated for mobile home use since they are built different from a regular stick built home. Those rocker switches do go bad but the only way to test them is with a meter.