Fan motor only runs on manual need help quickly

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  #1  
Old 12-30-07, 08:38 PM
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Fan motor only runs on manual need help quickly

Hi
I felt it getting cold in the house. 1st thing I did was check the pilot and it was on. I heard a buzzing noise but it was not very loud(didnt even notice it at 1st).
I started playing around with things and flipped the fan switch to manual on. The fan ran fine. While I was messing around I heard the burners come on. I waited a few seconds and the fan did not come on so I flipped it to manual on. That is where it is now. Im hoping it will keep the house warm this way and the burners will cycle on and off with the fan running constant.

It is a Nordyne Model MGHA-070AAFC-01.

Please help its going to be in the single digets tonight. Hopfully I will be able to find parts tomorrow.
Thanks
 
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  #2  
Old 12-30-07, 11:17 PM
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Now im really baffled. I thought I had figured it out to be the thermo fan switch but it suddenly started working. So now a ohm check will show everything is ok until it goes out again. Its pretty cheap so I wont be out much if I buy one just in case.
 
  #3  
Old 12-31-07, 01:51 AM
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how long did you wait for the fan? Sometimes a few seconds will not heat the trigger enough to start the fan.

It all depends on the temp setting of the fan trigger... Once the internal temp pass the pre-set, then the fan will come on.

Sorry I don't know all the technical terms... Basicly, it's cold outside, therefore, it takes a little while for your exchangers to heat up and trigger your fan.
 
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Old 12-31-07, 08:38 AM
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Your initial post didn't describe anything that was necessarily wrong. It sounds like you the thermostat hadn't yet switched the furnace on. Then it did and it lit normally.

Then it lit and you thought the fan should turn on right away, it shouldn't. The fan then turned on when it should.



There might be a problem, but it's not clear from what you describe.
 
  #5  
Old 12-31-07, 10:04 AM
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No, I keep my thermostat set at 72 which keeps it about 70-72 in the house. It was 64 when I realized something was wrong. 1st I flipped all the switches, then took the cover off and wiggled wires. I then started lightly tapping things with a screwdriver handle (Emmet's repair shop Mayberry N.C.). It was then that the burners came on. It also had been making a barely audible buzzing noise the whole time. What worries me now is my experience with this type of thing is that once it malfunctions it will soon malfunction again. And Murphy's law says it will be on a Friday night just after all parts outlet have closed. At least my 2 kerosene space heaters are full.

But the real problem now is with every thing working I see no way to determine which part is bad. Its going to be around 0 here later in the week.

Thanks for your replies
 
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Old 12-31-07, 12:08 PM
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Originally Posted by sidmabb View Post
But the real problem now is with every thing working I see no way to determine which part is bad. Its going to be around 0 here later in the week.

Thanks for your replies

You are probably correct. From your description there probably is a part that is failing and it will probably happen again.


Your best bet is to be prepared to deal with that when it occurs. You ought to have a multimeter that reads AC volts and ohms.

With the cover off the furnace, turn on a run the furnace repeatedly until you understand the sequence of operation ---the series of things that occurs over time that results in heat. Revire the schematic diagram of the furnace and identify the AC voltages that are present at various points in the furnace. Learn to "walk the circuit" of the 24 VAC circuit that controls the safeties and turns the gas valve on.


This is your opportunity to understand the way the furnace operates when it is working properly. One would hope that would make it easier for you to identify the point at which it fails if the problem recurs.
 
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Old 12-31-07, 04:36 PM
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If it heats good with the fan on manual, everytime, then we know your problem is not some issue with flame rectification, gas valve etc., regarding the buzz.

Try to see if you can pinpoint that buzz sound.

The buzz I'd imagine would be fan related. Relay, capacitor, blower motor itself (bearing or windings).

Try to spin the blower by hand with the furnace shut off and see if it spins a long time without slowing down = good.

Do you have central a/c also? A possible issue if you do, is that by having fan run on on/manual setting, that you have changed the blower speed and are utilizing a different (good)motor windings.
 
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Old 12-31-07, 04:40 PM
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Well was I ever right. Here it is 5:30pm New years eve and it quits again. So out comes the ohm meter again. I test and test and test then I go to test where the 2 wires go into the gas control box right next to where the thermocouple line is attached. When I touched the meter to one of the prongs it made a loud click and I now have heat again. I did get ahold of a buddy who has parts so I can call him if needed in the morn.

I think that 1st guy was right the 1st night I just had not waited long enough for the fan to come on but as it ran I tried a couple times to return it to auto and it stopped. Im getting closer.
 

Last edited by sidmabb; 12-31-07 at 04:44 PM. Reason: left some out
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Old 12-31-07, 05:11 PM
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Does the pilot at least always come on? Do you happen to know what system your furnace uses to sense the flame? You may have an issue with low gas restriction in pilot or tarnished sensing component. Then again you could have a bad gas valve.

Easy enough test to see that once the pilot is going, that then in a number of seconds that you get 24 A/C to the main gas valve terminals. If you do, and you catch it in the act of not lighting, then it sounds like a bad gas valve.

But if you do NOT get 24 volts at that time, then you'd have to look into why no rectification of the pilot flame.

Out of curiousity, what parts does your friend all have?
 
  #10  
Old 01-01-08, 12:26 PM
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My pilot is always lit. I found the problem though. It is the valve or at least the switch. If I play around with the wires where they plug into it it will click and then light. I noticed as I wiggle the wires the plastic on top of the switch will flex some. I'm guessing it is loosing contact inside until I wiggle it.

My friend talked like he should have anything I would need. He is a heating and air conditioning guy but not a good enough friend to come fix it at no charge LOL. When I 1st posted I hadn't yet thought about calling him.
 
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