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Robert
Robert, HVACR Educator
Category: HVAC
Satisfied Customers: 161
Experience:  Licensed Mechanical Contractor, 30 years experience, 20 years teaching experience
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My furnace is not turning on. It has power, and the indicator

Customer Question

My furnace is not turning on. It has power, and the indicator light has the correct "heartbeat". I can turn the fan on manually with the switch on the thermostat, and it comes on and seems fine.???
Submitted: 4 years ago.
Category: HVAC
Expert:  Robert replied 4 years ago.
Hi, I'm Bob.

I will need you to try some things when you are ready.
Customer: replied 4 years ago.
ok, i can do that now
Expert:  Robert replied 4 years ago.
Ok, I need you to go to the furnace and find the main circuit board. You will find some small gauge wiring connected to a terminal strip that has terminals labeled R, W, C, Y, G. I need you to jump the R terminal and the W terminal together without touching any other terminal. A small wire is appropriate for this. You will need to tape the blower door switch closed to make the unit run also if the door is off.
Customer: replied 4 years ago.
I taped the switch, pulled the fuse, and put the jumper wire in. As soon as I put the fuse back in the blower came on.
Expert:  Robert replied 4 years ago.
That is probably the fan cycle apower-up. Let it run through the cycle. You jumpered R to W correct?
Customer: replied 4 years ago.
yes r to w. My diagnostic light is flashing three times now. The book says 3= pressure switch open when should be closed
Expert:  Robert replied 4 years ago.
Is the small inducer fan operating?
Customer: replied 4 years ago.
is that on top? it is not running. the blower is still running
Expert:  Robert replied 4 years ago.
Ok, was the blowe running before?
Customer: replied 4 years ago.
No. I could turn it on with the switch, but it wasn't running on "auto"
Expert:  Robert replied 4 years ago.
Jumpering between R and W bypasses the thermostat and should bring in the inducer fan. It is the small fanwith the vent pipe connected to it. The sequence of operation is as follows: thermostat calls for heat (between R and W) Inducer fan starts, Pressure switch closes, Igniter energized and then trial for ignition.

Shut the unit off and remove the rubber tubes from the pressure switch (round, disck shaped device with small tubes connected to it) Blow through the tubes and reconnect them. tun unit on and see what happens.

Bob
Customer: replied 4 years ago.
no changes. This unit is less than a year old, btw
Expert:  Robert replied 4 years ago.
Ok so the small inducer fan is not running right?
Customer: replied 4 years ago.
No it is not. I put a better wire to jump the R and W. The blower fan is not running anymore, and the indicator light is flashing 3 times
Expert:  Robert replied 4 years ago.
Ok, that indicates a problem with combustion air-flow. The inducer fan needs to be running, Again, is it running?

thanks
Customer: replied 4 years ago.
no, it is not running
Expert:  Robert replied 4 years ago.
Can you check voltage?
Customer: replied 4 years ago.
no
Expert:  Robert replied 4 years ago.
Ok, That would be the next step We need to determine if there is power going to the inducer motor. I need to know if the inducer fan motor has failed or something else.
Customer: replied 4 years ago.
I don't have any way to do that
Expert:  Robert replied 4 years ago.
I have opted out so you do nat have to pay. You will need to be able to check power.

Thanks.
Customer: replied 4 years ago.
I have my multimeter now if someone can tell me what to check.
Customer: replied 4 years ago.
Can this be reopened?
Expert:  Robert replied 4 years ago.
I'll check.
Expert:  Robert replied 4 years ago.
For now, lets go ahead from where we left off. You need to check voltage to the inducer fan. there should be a molex connector that you can disconnect and check voltage when you try to start the furnace. remember, the inducer fan has to run before anything else can happen.

Edited by Robert on 12/2/2009 at 1:52 AM EST
Customer: replied 4 years ago.
Ok, what and where is a molex connector? How many volts should it be?
Expert:  Robert replied 4 years ago.
It is a plastic connector where the motor wires connect to the wires feeding it.
Customer: replied 4 years ago.
Is it a 2 wire connector?
Expert:  Robert replied 4 years ago.
Yes. Do the wires lead to the inducer fan? If so disconnect the plug and check to se if power is going to the two terminal in the plu (not the motor end connections) You will need to shut off the power. and get your meter leads on the connections and then turn the power back on. you should see 120 volts (give or take a few)
Expert:  Robert replied 4 years ago.
I see you are offline. I will be away from the computer until tomorrow sometime.
Customer: replied 4 years ago.
I could not get any volts from the two pins. I did get 121v from another source on the panel. I jumped two wires to the connector, thinking the inducer motor would come on, but instead I got an orange glow from somewhere (ignitor?).

Should the motor come on right away?

If my control panel was bad would everything not work, or could this connector be bad by itself?
Expert:  Robert replied 4 years ago.
The first thing that has to happen is the inducer fan starts up. Nothing else can happen until the inducer fan starts. The orange glow is the igniter. You have already jumpered between R and W on the terminal strip and you have 120 volts to the board plus you have a diagnostic light. tells me you probably have a bad board.

I am not sure what wires you are jumpering to get the igniter to come on but it doesnt sound like you are on the wires going to the inducer fan.
Robert, HVACR Educator
Category: HVAC
Satisfied Customers: 161
Experience: Licensed Mechanical Contractor, 30 years experience, 20 years teaching experience
Robert and 2 other HVAC Specialists are ready to help you
Customer: replied 4 years ago.
Got a new board today and installed it. It worked! Thanks.
Expert:  Robert replied 4 years ago.
That's great news!...Thanks!

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