Coleman 7680 Gas furnace - Blower shutting down HELP

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  #1  
Old 11-30-08, 07:42 AM
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Unhappy Coleman 7680 Gas furnace - Blower shutting down HELP

Hi everyone. I woke up this morning to a very cold mobile home.

From what I can tell? The furnace is lit and producing heat. Each time that the blower turns on? It starts...and within a few seconds the blower shuts down.

Anyone have any advice on what i can do to troubleshoot it? Way to broke right now to get someone out here to look at it on a Sunday.

I am in a 1977 Homette manufactured home. The only numbers I can see on the furnace are the 7680 I listed above. The BTU's are listed at 64000 on the faded information tag.

On the blower it is listed as 7680A590

Mat
 

Last edited by Mat_McGee; 11-30-08 at 08:11 AM.
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  #2  
Old 11-30-08, 09:58 AM
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Do you have a fan switch that you can turn the fan "ON" all times?

When the fan does run, and shuts down.. turn the power off, and feel the motor.. if the motor is hot, then it may be a sign that you need a new one.
 
  #3  
Old 11-30-08, 10:01 AM
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filters clean and squirrel cage "rounds" are free on dirt...can you do a fan only on the stat?does the blower cycle back on again or stays off?if the motor casing is hot to the touch it could be tripping the internal heat overload within itself...if its just cool/warm might luck out.the limit for the fan to run and stay on is fatigued or moved on the slide setting just above the burner section.do you see a silver covered control above the burner section......thats your fan and hi limit controller.fan should be at 160F-170F and the hi at 200F-210F.if this thing has any solid state board within the burner section you might be working on a delay timed fan ON instead of actual heat switch for that FAN ON
 
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Old 11-30-08, 10:27 AM
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I know mobile homes quite well. Anyway, if you woke up to a REAL cold house, let's say, you could conceivably have some other problem besides an actual blower problem malfunction.

Then when the blower tries to come on after ignition/burner heat, the cold air in the house sucks into the furnace, drops the heat exchanger temp so cold that the blower shuts off due to the furnace temp becoming lower than the fan off setting.

In theory such a problem as that could exist - if - the burner flame stays going while the blower shuts off.

But it also could be the blower motor. Try to spin the blower wheel to see if it spins easily. It should spin so easily that one little push should allow the wheel to spin in circles many times without stopping. But if it does stop quickly, you could have bearing problems. And if so, the heat generated by the resistance causes the blower to shut down on thermal oveload.

Or you may have a slightly weak blower run capactor. Motor shops can diagnose and sell you new one for like $10.
 
  #5  
Old 11-30-08, 10:33 AM
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Ok. I called my electrician "guy" and then had a friend stop over that does H&C on his way to a Pistons game (so he couldn't stay to help).

The furnace has not been kept up very well and he told me to remove the blower unit, clean the squirrel cage, etc. He said it spun fine when you spun it manually but that it could be unbalanced from the buildup, etc...either way it cannot hurt to take it out, clean and oil it, then retry.

The overheating seems to be what the issue is. When I found the problem this morning it was kicking on and then kicking off within seconds. I had shut the u nit off completely for around 30-45 minutes before my H&C friend came by. When we switched it on it came and and kept running! I was like..."No way, now it is going to work with you standing here: But after about 10 seconds it shut down again...he reached his hand back and told me it was running hot as hell.

So...I will take it apart and try that. It says to oil the unit every 6 months and I have not...nor do I suspect the previous homeowner had in the 4 years he was here.

Thanks for the help and I will check back in for more advice and/or to update the situation.

I really appreciate the input!
 
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Old 11-30-08, 10:43 AM
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The bottom line though is not the oil. It is not the oil if the wheel can spin good. Does it?

If it spins good, it probably is not the oil, as the direct immediate problem, even though it may have caused the problem. It could be something more damning, like the bearing is so shot that rather than it just being gummy and slow, - it is now eliptical, and pulls the inside of the motor off center and this causes the motor to slow and stop. Try to wiggle the blower wheel up and down and see if you get up and down clunking. Be sure not to confuse that play with end play, which is okay.
 
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Old 11-30-08, 10:49 AM
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if the squirrel blades are rounded off at all the air will not move as if there was no fan and trip as your is.....also if there is that much dust/dirt on them the motor windings might be covered or the air inlets on the motor clear it out as much as possible.tap the motor housing with the handle of a screw driver and loosen the dirt.soak those bearings spinning the squirrel the opposite way it normally runs
 
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Old 11-30-08, 11:13 AM
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And if a bearing say was gummed up, but no real detectable slop, you could take out the blower unit, oil the blower motor, then attach a 1/2 inch powerful drill to the shaft. If the shaft were 5/8 D-shaft instead of 1/2, you could get one of those sockets that are filled with those pins that slide inside it and conform, and slip THAT over the shaft and run the drill for a while, to get it to free up.
 
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Old 11-30-08, 04:37 PM
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Ok...I have the entire thing pulled apart. I was able to disassemble the entire motor (was not very easy). I cleaned the thing nearly spotless, oiled everything, etc.

Getting it together after I reset the blower motor mounts.

Here is to hoping it works. Beer 4U2
 
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Old 11-30-08, 05:34 PM
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Well...I got it together. I set it on heat...and waited for the blower to kick on. It did...and then a few seconds later? It kicked off again. I felt the motor and it felt fine.

So I switched the thermostat setting to Off with the fan on auto and sure enough...it kicked back on soon after and ran solid and strong. No problems from the motor. It was blowing warm air but I assume that is from it kicking on immediately after.

So...what should I check now? Working under the assumption that the motor is not shutting itself off from over-heating, etc.

Any more ideas? I was able to access the lower duct area of the furnace and clean it, I also pulled the cover off to see inside where the pilot light is. I did not see any settings I can alter that people have mentioned (lo-limit, hi-limit). Am I missing something?

**Update...now I went and set it back to heat. It kicked on and it has been on for well over a minute. Working better than ever. I guess I will see how it plays out over the next 2 hours.

Worked up from 60 to 72 and shut off on time. Then temp dropped to 70...it kicked on...and failed right away. So who knows.
 

Last edited by Mat_McGee; 11-30-08 at 05:50 PM.
  #11  
Old 11-30-08, 05:48 PM
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Originally Posted by Mat_McGee View Post
Well...I got it together. I set it on heat...and waited for the blower to kick on. It did...and then a few seconds later? It kicked off again. I felt the motor and it felt fine.
The fan switch maybe cooling off quicker, and shuts the blower down to allow the heat exchanger to warm up.
 
  #12  
Old 12-01-08, 11:50 AM
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Same thing is going on all throughout the day today. I am going up on the roof to check for a blockage in the roof vent in a bit.

This is the schematic for the 7680 (more or less, it is the 7700, but similar)

14 and 16 are the limit switches, correct? Should I remove them and have them tested?

 
  #13  
Old 12-01-08, 04:14 PM
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So is #7. Make sure all your connections that deal with this blower have good connections, also.

Only thing a vent could cause is limiting. You can check limiting without going on the roof to check vent. Either voltage check the incoming and outgoing 120 volts through these limit switches, or ohms test each one so they all read closed, with your furnace shut off for the ohms testing.

And yes, if cold air is drawn through the furnace, the blower may be shutting down if the fan switch thermodisc comes back down in temperature to it's pre-set off temperature. Have your Fluke all set up and ready to test these switches when it goes off, to see if the normally closed swithes open up.

Those 3 switches may be a fan ON switch, a fan OFF switch, and the high limit switch. Do not remove the switches to test. Be ready so you quickly test when blower shuts off.
 
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