Gas Furnace Blower

[Citlali]

I have a question about a 21-year-old "Day and Night" brand gas furnace (Model No. 376BAWO48075) which is working reliably with one exception.  The blower which is intended to go on shortly before the heating begins and goes off shortly after the heat goes off is still working, but inconsistently and unreliably.  (On most recent tests it wouldn't shut off even 'though the thermostat was turned all the way down.)  I've been told it may be that what I believe is called the "blower timer" or "blower switch" is wearing out and could stop working soon.  I would like to know if this sounds likely and if so, what may be involved in replacing or repairing the necessary faulty part or parts. 

We were successful, through your combined wisdom, to repair our washing machine this summer and would love to be able to have a similar triumph with the furnace.

Domi Arigato.

 

[RegUS_PatOff]

can you post the part number or picture of the Controller ?

may be similar:

ICM 275

[Bobice]

This example is based on advice from the Honeywell Tradeline L4064B. Check the test specifications provided by the manufacturer of your particular control.

Honeywell suggests the following steps, which we have edited and photo-illustrated for clarity and safety:

Check wiring: Assure that the control has been installed and wired in accordance with the manufacturer's installation instructions

Turn off electrical power to the heating system

Disconnect the fan at the fan motor or at the FAN LIMIT control terminal

Turn on electrical power to the heating system

Call for heat: Set the building thermostat to call for heat - this means that the "set" temperature on the thermostat must be above the room temperature. For test purposes you can if you like, turn the thermostat all the way "up" to its highest position - temporarily for this test procedure.

Don't forget to set the thermostat temperature back down to the desired level later.

Also if your thermostat has other switches such as "OFF", "HEAT", "COOL" - or "OFF" and "ON" be sure those switches are set to "ON" or "HEAT". More examples and details of thermostat controls are at THERMOSTATS

Watch the oil or gas burner: The furnace oil or gas burner should turn ON and subsequently the FAN LIMIT control should turn the burner back OFF when the temperature in the supply air plenum reaches the FAN LIMIT set point.

Watch the dial moving to confirm its operation. IF the burner does NOT turn off as expected, QUICKLY turn off power to the heating system and order further diagnosis.

(This particular gas burner shows some rust marks and flame leakage worries).

Watch out: if the fan limit switch does NOT turn off the burner when temperature meets or exceeds the fan limit setting, turn off the gas burner and power to the unit immediately so that you do not damage the heat exchanger by overheating it.

If the Fan Limit switch did NOT work normally, leave the system turned OFF and call for emergency heat service.

If the Fan Limit switch worked normally continue as follows:

• Turn off electrical power to the heating system
  
• Reconnect the fan motor where you previously disconnected it
  
• Turn on electrical power to the heating system
  
• Call for heat: Set the building thermostat to call for heat
  

Watch the furnace blower fan: The furnace blower FAN should come on when the plenum temperature has reached the FAN ON setting. Again watch the dial move on the FAN LIMIT control.

The furnace blower FAN should turn OFF when the plenum has cooled down to the FAN OFF setting.

This may not happen until after the thermostat has been satisfied (or you turn it back down to a low setting) and the oil or gas burner has shut down.

(The particular furnace has a filter that is insecure in this photo and so the heating system is unsafe as the filter could be sucked into the blower assembly causing overheating and a possible motor or electrical fire.)