Furnace Blower cycles On & Off - Burner Stays On

Problems related to residential installations.

Furnace Blower cycles On & Off - Burner Stays On

Postby SteveLeBard » Tue Jan 19, 2016 7:13 pm

I have a Sears furnace that when I turn it on at the the thermostat It runs for a short period of time (approximately 60 seconds), then turns off. The burner, however, does not turn off. After approximately 30 seconds, the blower turns back on. This cycle repeats itself continuously. The furnace is 30+ years old - we live in a mild climate and it doesn't get used a lot.
The Tag on the furnace states Manufactured for Sears Roebuck Model 867.762320, Ser No. H435 53757, MFR No. SUGE080CG01, Input Rating 80,000, It has a Honeywell S8610U Continious Re-Try, 100% Shutoff Ip, 90 Sec.Trial for Ignition
Can someone tell me how to troubleshoot this furnace? If it's too expensive to fix what would be a good replacement that would fit into the existing space?
Thanks for your help.
SteveLeBard
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- Furnace Blower cycles On & Off - Burner Stays On

Postby Freon » Thu Jan 21, 2016 4:11 pm

It's possible you only need to adjust a setting on the fan control switch. Google Honeywell fan control and look at what you see. Does your fan control have the circular dial? If so, what's happening is the air blowing thru the heat exchanger is cooling the heat exchanger to below the fan control ON setting. Let us know the type of fan control and we'll give you more direction.
Freon
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- Furnace Blower cycles On & Off - Burner Stays On

Postby SteveLeBard » Fri Jan 22, 2016 5:03 pm

I did try adjusting the Honeywell fan limit switch (was not far off) - no help. It's an old furnace and the FLSwitch has never been replaced. I don't see a model number anywhere on the FLSwitch. The FLSwitch has 3 settings 100 - 130 - 200 (approximate from memory). The FLSwitch does go through the cycle when the furnace is turned on.
Thanks Steve
SteveLeBard
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- Furnace Blower cycles On & Off - Burner Stays On

Postby Freon » Sat Jan 23, 2016 11:23 am

Remove the fan limit switch cover (usually you squeeze it) and watch the dial move when someone calls for heat. As the heat exchanger warms up, the dial should rotate. You will see three sliders and lettering on the dial. One end slider should be close to 200. That the high limit safety. DO NOT MOVE IT. It will turn off the burner if the heat exchanger overheats.

The middle slider is the FAN ON. As you watch your furnace heat up and the dial turns, when it reaches the FAN ON slider position the main blower will start.

The other end slider is the FAN OFF. Once the thermostat tells the furnace the house is happy, the burners stop and the blower keeps running. The dial will now rotate in the direction of decreasing temperature until it hits the FAN OFF slider.

Make sure your dial is rotating as I have described. What I believe is happening is once the blower comes on the air flow thru the heat exchanger is cooling the heat exchanger enough to more the fan control dial to the FAN OFF position. You can move the FAN OFF slider to a lower temperature to prevent this cycling. However if you move it to a very low temperature (below the house temperature) then the blower may never turn off.

You can Google Honeywell fan limit switch and watch a good YouTube video.
Freon
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