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Ask Suzanne Your Own Question
Suzanne, Owner/ Appliance Technician
Category: Home Improvement
Satisfied Customers: 232
Experience:  14 yrs in home experience - Appliance Service Field Technician
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i have a moncrief furnace model sh 75. the blower

Customer Question

i have a moncrief furnace model sh 75. the blower never shuts off. the heat comes on and goes off with temp but never shuts down the blower. it is killing my electric . there is a box in side that says manual and auto. it has been on auto for yrs. i just put it on manual i so far see no difference. please help
Submitted: 9 years ago.
Category: Home Improvement
Expert:  Suzanne replied 9 years ago.

The box you are describing is a fan limit switch. I am assuming if you have a moncrief this is not exactly a new furnace and you probably live in or around the NE US.

Question time -

Has the furnace blower motor ever cycled since you have lived in your home?

Have you recently changed the wall thermostat in you home?

Is there an "on" "auto" switch on your wall thermostat? Which is it set at?

I am assuming that you do not have central cooling is this correct?


Customer: replied 9 years ago.
Reply to Suzanne's Post: My thermostat is a basic round dial. no switchs on it.

I do not have the central cooling

it has never cycled on and off. i didn't really notice it was always on until a few years past.

thermostat is same as when i moved in here years ago.

I am in ohio . i know this is an old model by the henry furnace company. but it was well maintained over then years.
Expert:  Suzanne replied 9 years ago.

I thought you in Ohio but I didn't want to creep you out by me saying right off that I knew that! I am also assuming you are North of Columbus likely in the Cleveland area since most of these units stayed pretty close to their maker.

The fan switch is what is causing you constant on. Now, it could be bad or it was wired or set to be always on by the previous owner or installer. I would remove the cover of the fan switch and make sure the dial is not set to the lowest "fan on" setting causing it to be on constantly. Mark the setting location and feel free to rotate it carefully to see if the fan on can go off. If it doesn't you will need a new switch. Make sure to make yourself a good drawing of the wiring. Remove it and compare it to a new unit at your local heating and cooling or appliance parts store. These generally (depending on the length of the rod in the furnace) will run between $40 and $90.