furnace fan will not turn off

[thetransporter]

furnace fan will not turn off - its an older flame master, here are the two switches inside, fan keeps blowing after flame down . only way is to turn off is of course to power off the furnace.

what dial should i turn?
it appears person living in home before me switch something (just moved back in _ thank you

Any suggestions? thank you in advance

[Maxt]

Set fan off 110, diff 30 and the upper limit 200.0

[thetransporter]

thanks Maxt. I did what you suggested.

The fan is still running its been about 4 minutes.

What do these switches do exactly.

I understand that they limit the fan to run to safely cool down after flame out? but there is 3. I guess a range?

[Maxt]

The limit cuts the burner out should the fan fail and the furnace reaches that set temperature. The fan off is like you said, the temp that the fan shuts off, the differential setpoint is the span between fan on and fan off. So setting of 30 diff with 110 off would give a fan on setpoint of 140.
On the Flame masters, if the fan on temp was to high, the heat exchangers would develop cracks faster than usual, and if the differential was to narrow, the fan would jump on and off a few times after the heat cycle.
The control could be defective, but the other thing that happens to those controls, is the bi metal spring in the sensor portion between the heat exchangers gets fouled up with pet hair and lint, stopping the bi metal sensing element from contracting and turning the fan off.. Turn power off to furnace, remove the screws and pull it out of the furnace to check it .

[thetransporter]

thank you for all the information - so pull out the control (the lower one ?) and check the sensing element?

and where would be best to order one of these or buy one of these if i cant repair it. its for a flame master like you said. thank you again

[theken]

Is your ventilation fan switch turned on

[thetransporter]

Originally posted by theken
Is your ventilation fan switch turned on

thats all i have -

the thermostat is just TH/TH no switch.

[Maxt]

Originally posted by thetransporter
thank you for all the information - so pull out the control (the lower one ?) and check the sensing element?

and where would be best to order one of these or buy one of these if i cant repair it. its for a flame master like you said. thank you again

That whole unit comes out as a complete block. The version your furnace has is the really old version, the new one will have one big silver dial. The only places I can think of the that will sell it to a homeowner are AMRE or Davies electric.

[timdog]

Originally posted by theken
Is your ventilation fan switch turned on

I was thinking the same thing. you might have a ventilation switch near your thermostat or somewhere else in the house (nowhere near the furnace itself). it will look like a regular light switch. when i first moved into my house, I had something similar happen to me since I had never dealt with that stuff before .

[Maxt]

That is possible. Follow the wiring back from the motor itself. If the go back to the limit control box uninterrupted it probably spent have a "summer" switch.

[thetransporter]

the wire goes directly to the motor from the box.

thank you for the replies.

Maxt , what is the bottom switch called? (i understand the replacement will have a silver dial)

[schocker]

The limit switch went on mine because the humidifier pan was dripping onto it and short circuited it and it was on whenever the furnace had power until it was fixed. Maybe you have the same situation?

[thetransporter]

there is no other switch other than what i have in the picture.. thanlk yopu

[Maxt]

The bottom switch is the fan control. They are combined with the limit in the newer version .
This is what the replacement will be :

https://customer.honeywell.com/resou...0s/69-0117.pdf

[thetransporter]

Originally posted by Maxt
The bottom switch is the fan control. They are combined with the limit in the newer version .
This is what the replacement will be :

https://customer.honeywell.com/resou...0s/69-0117.pdf

thank you so much.

[thetransporter]

MaxT - that part (not sure if its the top or bottom gave way - when i power up the furnace it makes a buzz sound..... blower will not turn on .

so it looks like i willhave to replace it now.