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artbuc 07-31-2010 09:13 AM

Why is Inducer Fan Running?
This is a 13-14 year old York Furnace/AC. I didn't write down the model number but I will get it if necessary.

Neighbor calls and says the supply duct on her upstairs unit is sweating. I get there and find the basement floor around the unit is soaking wet. The condensate pump checked-out fine. Filter is clean and blower wheel is clean and running good. Plenty of air coming from supply registers. Eveidence of water running into main blower compartment and down the exterior. Disconnected drain line at coil outlet and it was dammed up with debris. Once cleaned, water ran out in large quantity. I believe this was the main problem. Once the floor got soaking wet, the high humidity condensed on the supply plenum above the coil and ran back onto the floor causing the problem to self-perpetuate.

Now to the question. When I got there the inducer fan was running and it was hot. Neighbor said it had been running for several days - she could hear it because the combustion air intake/exhaust is under her deck. She didn't think too much about it because she didn't know that the inducer fan should only be running on a call for heat.

This couldn't be a thermostat problem could it? It is a Honeywell programmable that the neighbor installed several years ago to replace the basic round Honeywell unit. Is it possible that this thermostat has a malfunction where it is calling for heat and cooling at the same time? If so, why didn't the burners light off?

Seems more likely that the inducer fan control is bad. I know on my Bryant's I have a separate inducer circuit board. Neighbor has all original paperwork including electrical but they were soaking wet and I am waiting for them to dry so I can look at them. Do you think water ran down and damaged the inducer control board? Seems like a strange coincidence that the inducer fan decided to start running at the same time the condensate drain line clogged up.

I unplugged the inducer fan. After I got the drain line cleared, we restarted the AC and it ran fine with condensate draining into pump and pump transferring fine. We turned off AC at the thermostat and I reconnected power supply to the inducer fan. Restarted AC and inducer fan did NOT come on. To be safe, I disconnected inducer fan before I left.

Tech is coming out Tuesday as part of their scheduled maintenance program but I was hoping to get a little insight so neighbor will know what questions to ask. Thanks.

Rusty999 07-31-2010 09:34 AM

Sounds like the board got wet. It may go away when it dries out, but will eventually need to be replaced from corrosion. The cause is usually water under the microrelay causin a short between the switched leg contacts.
Tell them to have the condensate pan cleaned out so it doesn't happen again. There's prob alot of rust and crud in there that will plug it up again.

yuri 07-31-2010 09:38 AM

Probably the inducer fan relay on the circuit board got energized when wet and stuck on. Won't fire up the burner as the W signal passes thru the pressure switch and limits to the gas valve (separate circuit). If the board got wet and damaged it is now UNSAFE AND DANGEROUS. The flame failure part etc is no longer up to the UL standards and I would not have it in my house. Drying it with a hair dryer is a lame and unsafe DIY fix to save a buck. Safety comes first not saving $$.

yuri 07-31-2010 09:39 AM

Welcome aboard Rusty.:thumbsup:

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