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BillyHvac
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22469
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Replaced furnace fan timer board. The part I replaced was

Customer Question

replaced furnace fan timer board. The part I replaced was the fan timer board.. The old board was a ST9160B1084. The new boards is a ST9120U. Checked wires 2x. power on and the blower starts and goes. no ignition and no flame.
Submitted: 2 years ago.
Category: HVAC
Expert:  BillyHvac replied 2 years ago.
hello,
on this board it is a sign of a tripped open safety...OR...no 24v to XFRMR and SEC terminals.
Can you see if 24v is going to those terminals?
Customer: replied 2 years ago.
I do not have a multimeter and my voltage meter is not for low voltage
Expert:  BillyHvac replied 2 years ago.
What was symptom of last board deeming it bad?
Customer: replied 2 years ago.
Nothing was working and there was power to the board. the tech said it needed replacement. Now replaced and the blower goes and goes but nothing else.
Expert:  BillyHvac replied 2 years ago.
Thank you,
Unfortunately this will require some investigation...but the only way to do so is with a meter for the low voltage. We know we have high voltage...the goal now is to see about the 24 volts. Does your replacement board have a automotive type blade fuse on the board?
Customer: replied 2 years ago.
Yes. I took the fuse out with power on and noted an arc. Not what I should do but it was the only way to see if power was there. and the status light on the board blinks green. The light on the gas valve blinks green as well.
Expert:  BillyHvac replied 2 years ago.
Great...that proves 24 v is present
So fuse is back in board and is not blown?
Customer: replied 2 years ago.
Right. Power is to the board and has been. Q: could the wires from the transformer be crossed polarity? or does that matter. I have the white to the I hhave the yellow to C and the Blue/Black to the X
Expert:  BillyHvac replied 2 years ago.
Black is L1..white is L2
Blue to xfrm and yellow to com
Customer: replied 2 years ago.
on the 24v side of the transformer yellow to C and the Blue/Black to the X. on the 120v side black is L1 and a L1 blue wire goes to the pressure switch on the cover and the white is in one of the neutral prongs. this is the way I took it off the old board.
Customer: replied 2 years ago.
I could upload a photo if helpful
Expert:  BillyHvac replied 2 years ago.
When thelight is flashing...how many times or wht pattern?
Customer: replied 2 years ago.
Just a slow on / off blink
Expert:  BillyHvac replied 2 years ago.
is it a bright/dim heart beat flash?
Customer: replied 2 years ago.
Exactly
Expert:  BillyHvac replied 2 years ago.
The heart beat = normal operation/stand by...
it does not code a limit or safety issue.
Theblue wire you say is on L1 is not showing on my print...you say it goes to pressure switch?..and then where?
Customer: replied 2 years ago.
there are 2 L1 prongs. one to the transformer and a blue one to the switch detecting the cover is on and closed.
Expert:  BillyHvac replied 2 years ago.
then you have the board with Neutral terminals beside the L1's and a white from transfoormer and white from power are on the Neu?
Customer: replied 2 years ago.
Yes.
Expert:  BillyHvac replied 2 years ago.
transformer BLUE to 24 VAC and yellow to COM
Customer: replied 2 years ago.
on the board blue to X and yellow to C. I assume this is the same as your last comment. And per the conversion chart that came with the board.
Expert:  BillyHvac replied 2 years ago.
correct.
There are many revisions of this board as it is a generic replacement for many units..so the terminals designation changes from unit to unit.
The light states normal but obviously there is an issue...does blower run non stop AND the heat does NOT work
Customer: replied 2 years ago.
That is what is happening.
Expert:  BillyHvac replied 2 years ago.
Thank you.
Well it is down to whether there is 24v on thermostat wire terminal R to C.
Until we know that we are at a stand still.
Customer: replied 2 years ago.
The thermostat board- I have 2 zones - lights up and the zone calling for heat opens the damper. I assume this means there is power to the thermostat? There is a transformer going into the board with R and C terminals.
Expert:  BillyHvac replied 2 years ago.
I had no idea this is a zone panel system...this changes things...
Can you get in the zone panel and locate R and W from the thermostat wires?
Customer: replied 2 years ago.
Yes
Customer: replied 2 years ago.
I have not touched this panel. It has 3 zones and I only use two.
Expert:  BillyHvac replied 2 years ago.
use a short wire and jump R to W at zone panel...tell me if inducer/draft motor starts in furn...this is for the wire terminals to furnace/equipment
Customer: replied 2 years ago.
Done. Same thing the blower runs and the inducer does nothing.
Expert:  BillyHvac replied 2 years ago.
Thank you.
Last test.....in the center of the circuit board is a terminal labeled DATA...
Do you see this terminal?
Customer: replied 2 years ago.
I saw this online and the board I have does not have this or it is not labled
Expert:  BillyHvac replied 2 years ago.
Here is the quandry....I assume you have a Hneywell Smart Valve with sv9500 series gas valve.
Tey call it smartvalve because it has a circuit board inside the gas valve which controls the inducer motor...ignitor...sensor...
So when thermostat calls for heat the gas valve starts the exhaust...not the circuit board. This is misdiagnosed the majority of time by techs not familiar with smart valve.
Is the gas valve still the original valve?
Customer: replied 2 years ago.
Yes original and it blinks green when power is on
Customer: replied 2 years ago.
The tech indicated that was normal.
Expert:  BillyHvac replied 2 years ago.
The valve would still code power present...but it would not engage the exhaust as it should.
There is actually a tester for the smart valve to determine the faults.
I can say that when it involves NOT having an exhaust fan it is 90% the valve and not the board. The board is usually related to a main blower issue.
I am afraid this would require continuing with a smartvalve tester or a smartvalve troubleshooting manual and meter
Customer: replied 2 years ago.
Does that mean I have no heat and need to call the tech back
Expert:  BillyHvac replied 2 years ago.
That is correct.
I apologize, but this is going to need verified on the gas valve circuit board operation...
Customer: replied 2 years ago.
Thanks

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