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Old 11-10-2008, 04:16 PM   #1
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Furnace blower not working right.


Ive got a 1992 Miller furnace in a mobile home. The heat come on and the blower starts about a minute later and then 1 minute later the blower shuts off but the heat inside the furnace stays on for about 1 minute than shuts off. The blower comes on again without the heat after i turn off the thermostat .The blower comes on for 10 seconds and shuts off again and repeats the same process about 4 times before finally staying off for good.Does anyone have any info that can help resolve this problem? Thanks.

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Old 11-10-2008, 04:23 PM   #2
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Furnace blower not working right.


Not an HVAC guy. . .if this failure is common for this furnace, the HVAC guys on this forum can nail the cause before I finish typing.

The heat come on and the blower starts about a minute later

OK

and then 1 minute later the blower shuts off

?

but the heat inside the furnace stays on for about 1 minute than shuts off.

Probably the hi-limit switch shutting it off because there is no cooling airflow, so the hi-limit switch is working normally.

The blower comes on again without the heat after i turn off the thermostat .

it senses the remaining heat in the system. This is independent of what the 'stat says. The temp.- or time-controlled switch for the blower has recovered and is working normally again, for a while.

repeats the same process about 4 times before finally staying off for good.

when all the heat has finally been dissipated.


The correct sequence for my gas furnace:

the 'stat calls for heat
the inducer motor starts
the gas flame comes on
when the heat exchanger is hot enough the blower starts, either by time passed or by sensing the temp.

when the setpoint is reached the gas shuts off
when the heated air gets cool enough the blower shuts off

some of these depend on time, some on temp. Some are adjustable.

There is also a hi-limit switch which trips if the gas is on but you don't have cooling airflow.


Your problem seems to be in the temp.- or time-controlled switch for the blower motor. It might be set too high, so it shuts off too soon, thinking that the flame is off because the air is too cool. Maybe one of these \/
http://americanhvacparts.com/Merchan...ry_Code=fl-tdf

The second choice would be the control board, but these don't see severe duty like the sensors.

Can you post a furnace schematic?

The good news is I couldn't find any class action lawsuits on the Web against this manufacturer.

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Last edited by Yoyizit; 11-10-2008 at 04:49 PM.
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Old 11-10-2008, 07:34 PM   #3
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Furnace blower not working right.


fan/limit switch needs replaced.
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Old 11-10-2008, 07:46 PM   #4
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Furnace blower not working right.


Here's another way to look at this.

Let's say the switch costs $50 and a service call costs $300.
50/300 is 1 in 6. If your chances are 1 in 6 or better that the switch will fix the problem, go ahead and replace it.
And the switch is old, anyway.

Just sitting here I'll give you better odds than 1 in 6, but it's not my money riding on this gamble.
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Old 11-10-2008, 11:22 PM   #5
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Furnace blower not working right.


Did you just move in to this place.
Or have you lived there, through 1 or more heating seasons before this one.

Some of the operation you describe is usual for that furnace.
Sounds like its getting excessive though.
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