Haunted Furnace Blower?


Old 12-02-02, 05:00 PM
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Haunted Furnace Blower?

Please help!
I've got a rather old (approx. 1984) Carrier A/C(electric)-Furnace(gas) combo unit-Model #58CP050 series 311. I'm using a Honeywell programmable thermostat.
Just recently my fan/blower started acting up while I have the heat on. Once the set temp. is reached, the fan turns off. Then immediately kicks on for a split sec, turns off, and turns on for a second again, and then finally shuts off.
In addition, this blower on/off hiccup now sometimes occurs when the fan turns on at the beginning of a heating cycle.

The furnace heats perfectly with no other problems, but I'm worried that this repeated start-up, stop, start-up, stop will fry my blower. It's also annoying as heck!

Is this a thermostat problem (that I can fix simply by replacing the thermostat) or is this a problem with the furnace itself?
Can a good handyman without gas furnace know-how (me) fix it on his own?
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Old 12-02-02, 06:08 PM
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A standard efficiency furnace has a fan/limit control that operates the blower.

If you have some electrical experience and a tester you may be able to do it yourself.

If your furnace has not seen a serviceman for a while though, now may be a good time.
Old 12-04-02, 03:35 PM
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Does your furnace have any solid stae boards in it? The HW programmable stats use inductive relays whch play havoc with furnaces with electronic boards. Even the when the t-stat is not calling for a certain circuit to be on there is voltage on the output terminal. The board often interprets ANY voltage as a signal to do something. The cure is to install an isolation relay in between the t-stat and the device it controls. IOW- wire the relay coil to G and C terminals on the t-stat and have the relay contacts operate the fan circuit. If you have a conventional fan/limit control, [no boards] then that is the palce to start looking.

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