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Matthew
Matthew, HVAC Technician
Category: HVAC
Satisfied Customers: 1994
Experience:  14 years experience in the HVAC field of service, installation, Manual J & D calculations
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Hello. Trying to replace original Honeywell ST9160B-1068

Customer Question

Hello. Trying to replace original Honeywell ST9160B-1068 with ST9120U-1011. Thought I had the wiring hooked up right but when I turn it on the blower turns on but the furnace does not ignite. Also on the circuit board the LED flashes so I know something isnt right. Any help?  I used the wiring diagram for ST9160 system with SV9510/9520 SmartValve control.  It notes that jumper plug must be attached, which I tried but it blew the fuse right away.  I have replaced the fuse so that isnt an issue.
Submitted: 2 years ago.
Category: HVAC
Expert:  Matthew replied 2 years ago.

Matthew :

Hello, My name is Matthew and I will do my best to help you today.

Matthew :

so you do indeed have a smart valve gas valve in your furnace?

Customer :

yes sv9520h 8034

Matthew :

and are you getting the flashing LED code on the valve when the blower is running and the furnace isn't igniting?

Customer :

on the valve no. only on the circuit board

Matthew :

what code is it flashing?

Customer :

one long blink, which according to the install manual means limit switch or burner limit switch is open. also i noticed that even though the thermostat upstairs is off, the blower still came on.

Matthew :

okay that little molex plug that came with the board and has one single wire in it that forms a loop in the plug you put that inplace on the board right?

Customer :

yes and it blew the fuse

Matthew :

That's not good

Customer :

i didnt think so either. made me wonder if maybe i had something wired wrong because the original board is labeled different than this one.

Matthew :

you see this board works with many different applications and on some applications the limit circuit and pressure switch circuit hook to the board via this port. On systems with a smart valve these circuits go tot he gas valve and this port isn't used. The plug is there to simulate to the board that the limit circuit is closed so it will not flash this 1 blink code. Something in that plug is shorting out or you may have it in upside down perhaps? It should just fit one way

Matthew :

yeah it will look different but it works all the same.

Matthew :

Can you tell me what terminals on the old board you corresponded to the new board?

Customer :

from the furnace- had the 6prong plug, plus white wire to neutral, black to L1. from blower yellow to heat, blue to cool, white to neutral, and red and black(that were at m1 and m2 on old board) to unused.

Matthew :

X and C from transformer hooked up and not touching anything?

Customer :

yes

Matthew :

do this. Take the thermostat wires off the board and then take a piece of wire and form a jumper that hooks the R and W terminals together. Try the furnace again and see if the fuse still blows or you get the 1 blink again.

Customer :

all the wires?

Matthew :

yeah

Matthew :

want to take the outdoor unit, thermostat, and all wires out of the equation to make sure the short is actually in the furnace.

Matthew :

all the wires hooked to the low voltage terminals, R, C, Y, G, W

Customer :

do i need to put in that molex plug as well?

Customer :

ok...now the furnace comes on, but the circuit board has 5 blinks now, smartvalve II limit switch is open.

Matthew :

yes the molex with the jumper should be in place for your furnace.

Customer :

yep. did that. furnace is on, smartvalve on furnace shows normal green light, but on the circuit board i have 5 blinks

Matthew :

sorry my cpu crashed let me pull all the manuals back up again so we are on the same page.

Customer :

no problem

Matthew :

the smart valve led is a normal heart beat though?

Customer :

yes

Matthew :

this 5 blink is indicating that it is receiving an open limit signal from the smart valve. Normally when this happens the smart valve will be blinking the open limit signal as well

Matthew :

Makes me think that there is something wrong with your board or with the wires from smart valve to board because the valve seems to think the limit is closed.

Customer :

yeah, im not sure what to do. get a new board or check the wiring. would this also have caused the problem where even though the thermostat is off the blower still came on? or does that have to do with that molex jumper not being hooked up at the time.

Matthew :

When you put the jumper from R to W you are simulating a thermostat call for heat. The blower comes on when there is an open limit. Which your board currently thinks there is.

Matthew :

The limits for your particular furnace run directly into the smart valve( the rectangular plug on the valve) So if they were open your smart valve would say so. Then out of one corner of the smart valve rectangular plug is what is called the "Data" wire which then relies any fault messages to the control board and that is when it would give you 5 blink code. But seeing as the smart valve thinks everything is fine something is happening from just beyond the smart valve on to the board.

Matthew :

The molex plug with the jumper is there because furnaces without a smart valve the limits run directly to the board where this molex jumper plug currently is. So the board has to simulate this closed circuit via the little jumper or it thinks the limit circuit is open and you get the 1 blink code.

Matthew :

what problems where you having that lead to replacing the board in the first place?

Customer :

last month had the blower motor replaced. the tech that installed it noticed that the old motor was wired to the cont spot on the board instead of the cool. he wired it back to the cool spot. after a couple of days started having an issue of the furnace igniting and shutting off every 15 to 30 seconds, with the blower cycling about the same way. then last week the blower wouldnt come on at all. when it tried to come on it just made a thud like sound.

Customer :

after checking some things online it seemed like it was either a valve problem or a board problem. I figured board because of the way it had been wired before.

Matthew :

If the blower was hooked to the cont spot and nothing was on the cool spot all his time then your furnace fan would not come on in cooling.

Matthew :

If the furnace ignited and stayed on for just a few seconds and the ciruclating blower never kicked in that is a dirty flame sensor.

Customer :

he also said this would cause the blower to run nonstop.

Matthew :

not true

Matthew :

the cont terminal is there so that if you want to use a slower speed for the fan "on" option at the thermostat you can.

Matthew :

If no wire is hooked to cont then when your thermostat switch to fan "on" it just runs at the heat speed.

Matthew :

If you have a wire to cont and you turn your thermostat fan switch from on to auto and there is no call for heat or cooling the blower will go off.

Customer :

so im guessing that i have it hooked up right, just either an issue with the board or the wiring?

Matthew :

it seems to be hooked up right. what is happening is very odd and I think you may have some bad wires/molex plugs in your furnace that are causing all kinds of chaos. this is not something that happens often but it does happen. about 1-2 times a year I will have to order a complete wiring kit for a furnace from the factory to resolve problem childs like yours.

Matthew :

this is a brand new board right not a used one?

Customer :

brand new yes.

Customer :

if i have to order a wiring kit, do i order for the smartvalve

Matthew :

You can try exchanging the board and see if you just got a bad one from the factory, but I'm guessing you will find the same issues.

Matthew :

know you order for the G1D1AU050 and it will come with all the harnesses and plugs that are in that furnace including the ones to the smart valve. The only thing it will not come with is the igniter and it's plug to the smart valve, but you don't need that.

Matthew :

know=no sorry

Customer :

ok i guess i will give that a shot then

Matthew :

Sorry. hope you track down the issue.

Customer :

just one more thing. i know i have the wiring for the thermostat hooked up right, but the 2 outside wires, a red and a white wire is it red to the y and white to the w?

Matthew :

outside wires are one to Y one to C doesn't matter which to which

Customer :

ok...thats not how those were wired.

Matthew :

that would blow the fuse

Matthew :

having one of the outside wires hooked to W

Customer :

yep, i think thats the way i had it

Customer :

maybe i should try wiring it correctly and see what happens

Matthew :

worth a shot

Customer :

but does that have anything to do with the other problem with the limit switch?

Customer :

im going to go downstairs and wire the thermostat. brb

Matthew :

no it wouldn't. If you had a wire under R and W from the outdoor unit then as soon as the heat kicked in and energized the W terminal your fuse would blow.

Customer :

double checked the wiring at the thermostat...white to w, blue to y, green to g, and red to rh. there is no rh on the circuit board, i assume it goes to r?

Matthew :

yes and at your thermostat there should be an RC terminal with a small jumper that then hooks to the RH.

Customer :

yep

Customer :

so i wired it back up, turned on the thermostat and jacked up the heat and it seemed to cycle ok, when i turned the heat back down the furnace shut off and then the blower turned off a couple of minutes later. dont know if that is normal or if the blower is supposed to turn off immediately. still had the 5 blinks on the board but the valve was showing normal. maybe something with the board? i guess all i can do is keep an eye on it.

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