Inducer Fan Not Turning On - HVAC - DIY Chatroom - DIY Home ...

Hi guys, thanks for helping me out, great forum! I have an issue with my furnace I'm really hoping you can help me out with. I have a Ultra V Tech 80 furnace and last week I turned it on for the first time since last winter, it blew hot air great. Some time over the following few days it got colder and I realized the furnace wasn't on anymore. I pulled off the front cover and it was blinking twice which corresponds to "Pressure switch stuck open, should be closed."

When I turn the furnace off and back on again, nothing happens. The inducer fan does not start, nothing turns on, nothing clicks, it only makes a constant low hum from somewhere inside. I took a look at the old Honeywell control board and there was brown charring around one of the parts so I just replaced it with the newer updated model, a ST9120U1011. I hooked it all up and still get the 2 blinks.

Here's what puzzles me, shortly after I turn the system back on, I can only assume it's trying to start the inducer motor to close the pressure switch and start the ignition sequence. However, if I pull the vacuum hose off the inducer and suck on it, I can easily get the pressure switch to close, and if I keep sucking, the inducer fan pops on and the furnace fires up perfectly. As soon as I stop sucking, the pressure switch opens and the heat stops. BUT, the inducer motors continues to run so if I put the vacuum hose back on the inducer motor, it'll continue the suction, close the pressure switch and the furnace works fine until it reaches temperature and shuts off again. Then once again it won't come back on because the pressure switch won't close.

So, what is my problem? Does the control board close the pressure switch causing the inducer fan to come on, or does the control board initialize the inducer fan which causes the pressure switch to close? If it's the former, I would assume my pressure switch is bad.

Source: http://www.diychatroom.com/f17/inducer-fan-not-turning-119858/

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