Fan not responding to temperature, runs non-stop. Furnace power on, fan runs. Pilot works. Thermostat [Hunter model 44110 programmable] calls for heat, burner fire successful. Fan already running. Thermostat setting met, burner turns off. Fan continues to run through succeeding cycles. High limit switch okay. New [unnecessary] fan control switch. Open circuit at fan control switch does not stop fan. Remove thermostat, power up and the fan runs. This is a Model HBD 80, John Zink Warm Air Furnace, circa 1954 or 1955. No schematic found, only a block diagram. Suggestions appreciated, someone said it was okay to let it run, it should last a long time.

It will not hurt for the blower to run all the time that's the reason you have the fan on switch on the thermostat. Yes it will add to your electric bill but not much. With the fan running all the time it mixes the temps in the house. Taking cool rooms and warm rooms and mixing the air to make it a more even temp in the house. I have a heat pump and I run my blower around the clock.

T-Top: Thank you for responding. Nothing seems to turn the fan off except the line switch to the furnace cabinet. There is a transformer on the cover plate of a junction box in the lower compartment where the fan assembly is mounted under the furnace proper. I looked there earlier and it appeared to me that the wiring was secure and not altered from the time that the fan responded to temperature change. I am considering drawing a schematic of all the circuits in the furnace, to confirm no mistakes in wiring. Thanks again.

As usual, T-top is right. If you still don't want to let it run, ''new [unnecessary] fan control switch''. Did that include the relay that actually controls the fan? Follow the wires back from the blower motor. One should connect to the white wire from the house. The other should be one of 4 wires going to a little box. One of the others goes to the black wire from the house. Check for 24 volts between the other 2. If so, the problem is in the limit switch or something. If not, the relay is bad. Replace it.

labman: Thank you, that is the direction I should be going, and I will. The gas company would be shocked if they knew how little we ran the furnace while finding this out. I will find that (relay) and make the schematic. I will let you know when it's done. Ocumenting this episode may help others later. Thanks again to everyone. Melvin

Hello All, There is no relay. Someone wired this creature with some extension cord wiring, and made it difficult to trace through flex-metal-conduit. Block diagram explicitly shows two parallel circuits coming off the 110 vac supply: The fan circuit with fan control switch in series with motor; The Thermostat circuit properly supplied from the 25 vac transformer output in series with the solenoid valve controlling gas feed. There seems to be no problem with the gas system or self energized pilot and control vave. The next shot seems to be a separate feed line to each powered input. I'll try to assure you later of my progress.. . Melvin

If somebody has run the 120 volt feed to the fan through a switch meant for 24 volts to the coil of a relay, it is no wonder the contacts have welded leaving the fan permanently on. Extension cord? How heavy? I don't think the typical 18 gage is heavy enough for the power to the fan. For the power to the fan, I would pick up some stranded THHN or something #14 if the circuit breaker is 15 amps, or #12 if 20 amp. Since you have a transformer supplying 24 volts to the thermostat, buy a 24 volt coil 120 volt relay and 10 amps or larger. Buy a new limit switch. You may have to go to a HVAC supply. Take the old switch, and let them match it. Connect the black wire from the house wiring to the line side of the relay, and the load side to the fan. Also connect the other fan lead to the white wire from the house. Come off the side of the transformer that the red wire to the thermostat does and run to the new switch and to the coil of the relay. Connect the other side of the coil to the other side of the transformer. That wiring doesn't need to be 12 or 14.

Many more Thanks to T-Top and labman: The unthinkable. With all else failing to make sense, of which it appears I have no common sense. Replaced all wiring, double checking al steps, same problem. New action, open the circuit from the motor at the fan control swith. Power up, fan runs. Musty be a short in the leg of the fan motor connected to the fan control switch. Approximately 1 Ohm from one lead to case, 2 Ohm from other lead.
Thanks to all, I'll soon be on my way to get new motor.. . Melvin
PS labman, my little poodle is only a 2 ponder, but I'm not throwing this 3 year old back.

The fan control center contains a relay and a transformer.

Hello, this should finish the job. Replaced shorted motor with a Fasco [1/8]-[1/5]-[1/4] HP which I set up for 1/4 and will monitor airflow at current draw with single speed at 1075. I gave this motor an initial oiling of synthetic oil. Everything circuitwise seems to perform appropriately. Sure is nice to not listen to continuous running of fan. Thanks again to all of you great responders.. . Melvin

Quote:

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Originally Posted by KeepItSimpleStupid

The fan control center contains a relay and a transformer.

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A relay saves the expense of an unneeded transformer that would only complicate things.

labman:

Sometimes you can't separate the two components easily and replace them separately.

Do you ever read the threads before answering?