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BillyHvac
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22092
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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I replaced a ST9160B-1076 blower motor control board with a

Customer Question

I replaced a ST9160B-1076 blower motor control board with a Honeywell ST9120B , universal replacement board when suddenly the blower motor no longer worked. Originally I replaced the motor itself thinking it was the motor. When that didn't work I called a "professional". They identified that the board was bad. I got the generic Honeywell replacement board and moved wires from original to new according to the instructions leaving one wire from the original board without a corresponding connection on the new board. Now the original blower motor works under continuous fan mode but it is also always on even when the thermostat is in Auto mode regardless of whether temperature on thermostat is set for Heat or A/C and whether or not the thermostat temperature is set at a level that should activate either A/C or heat respectively. No signal for A/C or Heat is triggered in either case. There is no delay when the motor comes on... It is just always on under regardless of thermostat settin
Submitted: 1 year ago.
Category: HVAC
Expert:  BillyHvac replied 1 year ago.
Hello,
can you tell me what terminals you have the blower wires on?
Customer: replied 1 year ago.
blue on heat, black on cool and white on neutral
Expert:  BillyHvac replied 1 year ago.
Thank you,
and is the fuse on the board still intact?
was there a limit fault before you replaced the board?
any diagnostic light activity?
Sorry for all the questions but it saves time..
Customer: replied 1 year ago.
The original board had no diagnostic light. The new Honeywell replacement board green light blinks slowly constantly which I believe indicates normal operation.
Expert:  BillyHvac replied 1 year ago.
Thank you,
and thermostat wires are on what terminal now?
Customer: replied 1 year ago.
there are two sets of wires going to the thermostat. One set has only the red wire in use, the others are cut. That red wire runs between Y on the thermostat and Y terminal on control board. The other set of wires from the thermostat has red from R on thermostat to R on control board, white from W on thermostat to W on control board and green from G on thermostat to G on control board. There is also another set of wires connected to those terminals. It has two wires in the sheath and goes up through the ceiling I presume to the outside A/C unit... Red from that is connected to Y on control board and white is connected to C on control board.
Customer: replied 1 year ago.
I have a full day today and won't likely be able to respond much. Tomorrow I will have a lot more time to make our back and forth quicker. Thanks for your help.
Customer: replied 1 year ago.
Are you available now to work on my problem? I am for a couple hours.
Customer: replied 1 year ago.
Do you have any other questions about my configuration or connectivity? I do have the ability with a rudimentary DC voltmeter to tell you voltages if you give me the exact terminals to test between. I do know the transformer was tested as OK.
Expert:  BillyHvac replied 1 year ago.
Thank you..
with G wire removed from circuit board...does fan still run continuous?
Customer: replied 1 year ago.
I am available today until 5pm. I don't know why I didn't see your response yesterday, but I didn't get an email notification you had and it was just by accident I saw it this morning by clicking again on your email from the day before yesterday. The answer to your question is: if green wire is removed from circuit board, the blower still runs continuously.
Expert:  BillyHvac replied 1 year ago.
Ok,
I made a call to tech support.
Your circuit is a bit different and will not accept the 9120..you have to stick with the 9160 series.
Your current board is reading an open circuit and is running blower in safety default mode.
Short story is the 9120 works on hundreds of models but not this one.
see link below
http://www.americanhvacparts.com/p-21254-furnace-control-fan-timer-circuit-board-6-plug-molex.aspx
Customer: replied 1 year ago.
Can you tell me then why the manual lists the board I've replaced as being compatible in the manual? The specific replacement board I have manual says: ST9120B, U Would you say that my supplier made an error giving me this board and I should request a swap? or other compensation? What is the specific part number I should tell them I need to replace my original ST9160B 1076 board with since I guess I'm having to do their work for them. Before this board they had given me another board that didn't even look close to being comparable to the ST9160B. I took it back and they said they'd made a mistake and replaced it with the 9120. You are saying the whatever part they replace it with will have ST9160B in the part ID?
Expert:  BillyHvac replied 1 year ago.
There are Ducane models that take the ST9120.
However your unit is not one of them.
There are many versions of this board. The best thing is to get a ST9160
The ST9120 does replace many boards..but not all. Just tell them you had a hvac contractor make a call to tech support and found that you need the ST9160.
Customer: replied 1 year ago.
the supplier checked with Ducane and they insist the Honeywell 9120 board will work... it has replaced the 9160 in all their applications. The supplier installation manager says that the fan will continue to run if there is an open circuit usually at the burner igniter or rollout switch and he says this will occur whether or not the thermostat is in cooling or heat mode until the open circuit is corrected. Perhaps the diagnostic light is indicating that and I misinterpreted it when you asked originally. What is occurring is that the green light is on 2 seconds then briefly off, then back on 2 seconds, then off briefly and so on... the instruction manual does say that one flash indicates limit switch is open... I may have guessed this was the dim/on heartbeat normal operation and really it is a brighter and not regular enough to be normal and is in fact telling me that the limit switch is open?
Customer: replied 1 year ago.
do you know of a supplier that still carries a 9160 control board?
Expert:  BillyHvac replied 1 year ago.
Ok here is the issue...If you had a ST9120U it would replace the control.
But there are tons of ST9120 units....copy and paste below link...but pay careful attention to numbers and letters AFTER the 9120.
Now....if you are on limit...yes it will cause this. That is why my first 3 questions were:
"and is the fuse on the board still intact?
was there a limit fault before you replaced the board?
any diagnostic light activity?"
Your first issue was no blower so we steered away from limits. Are you familiar with a flat plate on the front wall behind the gas valve?
Customer: replied 1 year ago.
I'm not sure where the gas valve is. I can trace the gas lines back into the wall but I don't see any plate. There are screw and levels that can shut off gas but that's all I'm aware of or is the gas valve inside the furnace?
Customer: replied 1 year ago.
screws and levers I meant
Customer: replied 1 year ago.
I have another technician here now... he gets high and low voltage coming into the control board, but no voltage coming out
Customer: replied 1 year ago.
the technician says the light blinking there is now is the "heartbeat" normal situation
Expert:  BillyHvac replied 1 year ago.
Heartbeat will be normal....do we have blower and all operation now?
Customer: replied 1 year ago.
The technician spent over 2 hours and checked every limit switch, fuse, gas valve, thermostat (even put new thermostat on). Nothing changed the status of fan on only. Put old board back in place and as before blower motor didn't work, but A/C worked and the motor that starts before burners ignite worked as before and tapped old board where the motor relay switch was an major spark so obviously it was the relay on the old board that was a problem. But Ducane does not supply the old board and the 9120 is the only option for replacement. His conclusion at this point is that the new board is faulty also. It heats up that furnace inducer motor but doesn't turn it on even when Heat is not on, which is the only thing it apparently does other than run the fan continuously. A more senior tech will be coming out tomorrow morning to see if this last tech had missed something but as of right now it looks like I will be returning the new control board and get a replacement part to see if that works. If you have any more specific knowledge of what version of the ST9120B universal Honeywell board works with my Ducane with original ST9160B 1076 board I'd greatly appreciate it. I mean I presume there might be slightly different vintages or production runs where slight modifications might have been introduced that might make a difference. Thanks, Billy
Expert:  BillyHvac replied 1 year ago.
the 9160b is still available...you can find many choices by Googling.
The 9120U will also be a fit
anywhere from 130 - 150 bucks....even on ebay
Customer: replied 1 year ago.
I realize googling and ebay shows it as 9160, but when you delve deeper you find that it really is the 9120 substitute offered since that is the "official" replacement and is SUPPOSED to work.
Customer: replied 1 year ago.
Even Ducane technicians say that the Honeywell 9120 will work
Expert:  BillyHvac replied 1 year ago.
There is no such thing as a Ducane Technician. Only techs that work on this n that and ducane is one of them. Ducane is not an upper end mfg and does not offer factory trained techs like Carrier, Trane, York...Ducane is a unit sold under many generic terms.
And the 9120 you find as replacement is 9120U.
I wish you luck.
Customer: replied 1 year ago.
A more senior or knowledgeable technician came out last Friday from the same company as last Wednesday. He checked some things and then decided to try the system with the old board installed and wired in. It worked! Apparently tapping that relay on Wednesday broke the relay loose. The second technician didn't recommend I use the old board because he then took off the board and looked at the back and it is covered with darkened resistors and burn marks. He made an offer to install another new 9120U board from the same distributor as the one I had but they would guarantee it with warranty, etc. for the life of the system for a high price. I declined and continued to use the system with the old 9160 board to today and it has worked flawlessly as it always had until the failure. But I can't afford this failure in the winter and as far as I knew my new board did not work so I needed to take it back to my supplier and get a refund or replacement. I could get the 9120U board online for $95 to $110. The one I have cost $240 which I paid because I just wanted to get the system working quickly.But last Wednesday that technician looked through the 9120U installation manual and asked if I had a bag with wires in it and I said I did and he mentioned something about a jumper. I said I hadn't done that and didn't know about it. That's where he dropped it. So I thought about that and finally read the manual better and saw for the 9160 that a jumper was needed and was one of the 5 must have requirements listed in a triangle that were highlighted. I checked wiring of the jumper and it had a low voltage connection but between two different pins on the connector than what was on the sole jumper I had in the bag. But before I tried to get my money back for a faulty board I thought I should at least put in that jumper and if it didn't work use a make-shift connection between the terminals that it looked like it should have if the jumper didn't work. I hated to disconnect the old board since it was working so well and didn't want to screw something up, but I did it and reconnected my 9120U board as I had before but this time with that jumper installed too.. result... the system works fine with the new board! So the failure was me not putting that jumper in since I never read the installation instructions for my specific board replacement. The initial determination of a bad board by the first company was correct before I ever contacted you. The second guy from that company who was told to bolt and just leave by the owner of the company was in the process of checking to make sure my 9120U board was the right board with the supplier when he left. If he'd been allowed to continue he might have found the missing jumper. The first guy from the 2nd company saw the problem but didn't follow it up. The 2nd guy from the 2nd company didn't ever look at my new 9120U board because the old board was installed and he got it working but it was obviously damaged so his goal was to get me to buy a replacement board from them not check out my replacement 9120U board... anyway a comedy of errors. By the way the diagnostic light on the new 9120U Honeywell board does have a distinctive pulsing light that looks normal, not flashing like before. I guess the single flash was caused because of the lack of jumper that made voltages drop to mimic a limit switch failure. Anyway, Billy, this was a long final response to give you knowledge of what the real situation was since you did try to help my situation. Maybe it will help you help another bonehead in the future better... :) Thanks again.

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