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I'm replacing an St9168B board with an st9120B,U board and I…

I'm replacing an St9168B...

I'm replacing an St9168B board with an st9120B,U board and I have two wires marked 24vac (50/60 and hzla) that have no corresponding plugs on the Universal board. Where do they go?

Contractor's Assistant: I'll do all I can to help. How long have you been dealing with this?

Just now.

Contractor's Assistant: Do you plan on doing the work yourself?

I have the new board ready to go except for these two wires.

Contractor's Assistant: Anything else we should know to help you best?

I have two other wires marked M1 and M2 which I am fairly confident that they are not used on the new upgraded board.

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Answered in 51 minutes by:
1/17/2018
airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8,908
Experience: Furnace, A/C and heat pump specialist.
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Should post say old board is a ST9160?

If so

The 24VAC should go to X and the COM should go to C

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Customer reply replied 1 month ago
I did that, I put the first wire under the 50/60 on x and the second wire under the hzla on c. I turned it on and I'm getting the message that the limit switch is open?

Try switch the X and C

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Customer reply replied 1 month ago
Did it, still get the message that the limit switch is open. I also note that my Nest thermostat doesn't light up.

What was the initial problem that caused you to change board and what is model on your furnace?

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Customer reply replied 1 month ago
The tech that came to see what was wrong with the furnace (it would make noise like it was going to start and then stop before the gas lit) and she said the board was bad and showed me the burn spot on the original board. The model number is ***** Says its an Ultra.

Did you adjust the dip switches on new board?

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Customer reply replied 1 month ago
on, off, off, off, on. (30, 120,4,30, recommendations for Armstrong board 9160B1068)
Customer reply replied 1 month ago
I old board was ST9160B1068 (not A1002).
Customer reply replied 1 month ago
The manual that came with the board lists it as an Armstrong. The board itself says Honeywell, but they told me it was made by Armstrong.
Customer reply replied 1 month ago
The manual that came with the board lists it as an Armstrong. The board itself says Honeywell, but they told me it was made by Armstrong. And would the limit switch open keep my thermostat from coming on?
Daniel Plourde
Daniel Plourde, HVAC Technician
Category: HVAC
Satisfied Customers: 429
Experience: I've been in the HVAC buisness since 2008 working on residential, commercial, and industrial buildings
Verified

hi I am dan I can help you with this. which wiring harness adapter are you using?

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Customer reply replied 1 month ago
I'm not sure what you're talking about. I'm replacing an ST9160B-1068 circuit board with a ST9120B, U board.
Customer reply replied 1 month ago
I'm not sure what you're talking about. I'm replacing an ST9160B-1068 circuit board with a ST9120B, U board. I've make all the changes that I believe are correct(?), but I'm getting the error message that the limit switch is open (and my nest thermostat is not coming on).

your replacement board is a universal board so it comes with different wiring harness adapters that are used on the 9 pin plug depending on what board you are replacing. the reason you are getting the error code is because the 9 pin connector is incorrect

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Customer reply replied 1 month ago
There is no 9 pin plug, only the j1 and the j3 which are six pin?

sorry I meant 6 pin. it is J1 that the adapters are used on

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Customer reply replied 1 month ago
I used the adapter that connects the 1 pin to the 6 pin.

do you have a jumper plug pluged into yhe j3 connector

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Customer reply replied 1 month ago
I have the 6 pin connector plugged into the J3 and the jumper plug in the J1.

what is the model number of the furnace?

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Customer reply replied 1 month ago
G1n80ar075d12a-1a.

are you getting the error code on the new circuit board or the gas valve

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Customer reply replied 1 month ago
G1n80ar075d12a-1a.The new board.

ok make sure the jumper on J1 is jumping pin 1 and pin 6 together

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Customer reply replied 1 month ago
Assuming the plug is good, it is (top left corner marked 1 to bottom right unlabeled).

yes

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Customer reply replied 1 month ago
what? What next?

just to confirm those 2 pins are jumpered and you are still getting 4 flashes from the circuit board?

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Customer reply replied 1 month ago
On this universal board, I'm getting one (1) flash which indicates that the limit switch is open.

can you take a picture of the board installed and how it is wired and post it here

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Customer reply replied 1 month ago
I can try. I'm not sure you'll be able to tell anything with the jumble of wires. Is it possible that the hvac tech who diagnosed that I had a bad circuit board could have missed a bad limit switch? The furnace would come on, get ready to fire then shut down. There was a burn solder connection on the old board.

the limit switches on your furnace are monitored by the smart valve, not the circuit board. if one of them were open you would get the error code on the smart valve.

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Customer reply replied 1 month ago
I have a photo but I can't get it to post into this area.

you can use the attach file link to attach it, for assistance with adding files you can contact customer service and they can help you with that.

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Customer reply replied 1 month ago
Did you see the pic?

ok thank you for that. the jumper in j1 is wrong. it is possible that the jumper plug was wired wrong from the factory. if you do not have the correct jumper you may have to modify that one by removing the pins and reinserting them in the correct terminals. they should be directly across from where they are now.

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Customer reply replied 1 month ago
I noticed that in the spec diagram for the smartvalve that it showed the J1 plug connection going from the top right to the lower left. Is that the correct configuration?

see the picture above

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Customer reply replied 1 month ago
Thanks, ***** ***** that a try in the morning. Let you know if that works.

ok let me know

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Customer reply replied 1 month ago
I checked with Honeywell and they said (despite the schematic being opposite of the instructions in table 6) that the plug is correct and do not recommend changing it (wouldn't say whether it might damage anything). Do you know if that is a risk?
Customer reply replied 1 month ago
Any one there? I still don't have my problem solved.

it wont damage anything, the wires need to be switched

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Customer reply replied 1 month ago
Well, that might have fixed it. I held the shut off switch down and everything seemed to fire up like it should. However, the single flash (limit switch is open signal) continued to flash. My Next thermostat came back on, but said it needed to shut down to recharge it's battery. Will the signal for the limit switch go off after everything charges up and it runs a bit, or is something else wrong?

the light will slow flash when in normal if it was an error it would prevent the unit from runing

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Customer reply replied 1 month ago
Well that looks like it fixed it. Assuming nothing else happens, I'm good. Thank you very much. I would think that Honeywell should change the very clear part of their instructions (table 6) that has it wrong, or at least let people know.
If you have any more questions please let me know and if this has helped you I would appreciate it if you could rate me on my service by selecting one of the 5 stars on your page.
Daniel Plourde
Daniel Plourde, HVAC Technician
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Customer reply replied 1 month ago
We may not be done. I had the thermostat set to 60 and keeps running. It's up to 63 and does not seem interested in shutting off.
On the circuit board remove the W wire and see if it turns off
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Customer reply replied 1 month ago
It's still running. Air doesn't feel warm and I don't hear the burners.

is the fan set to on at the thermostat or auto?

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Customer reply replied 1 month ago
I'm not sure. It's a "Nest" and when I went to check it, it set fan run on "schedule" and before I could look further it said it had to shut down to recharge again.
Customer reply replied 1 month ago
It evidently wasn't charged enough before I pulled the w wire (if that controls power to the thermo).

ok then there is a problem with the thermostat. by removing the w wire turns off the call for heat to the furnace. the thermostat could still be calling for fan on the g wire.

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Customer reply replied 1 month ago
what do I do?

if the thermostat keeps turning off and recharging then it may be bad. I would contact nest technical support to help diagnose it

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Customer reply replied 1 month ago
Should I reconnect the w wire and wait and give time for the nest to recharge? It was registering as working while the furnace was running. Even if the fan was on, it shouldn't have kept heating beyond where it was set (62%)?
Customer reply replied 1 month ago
Should I reconnect the w wire?

the w wire does not need to be connected for the thermostat to charge

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Customer reply replied 1 month ago
That doesn't answer my question. Should I reconnect the w wire?

for the heat to work you will need to reconnect the w wire but the furnace may stay running if the thermosat is still not working

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Customer reply replied 1 month ago
Well I'm not sure what a back up battery has to do with the furnace not responding to (shutting down when it reaches temperature) but I'll check with them in the morning. I note that you only get the recharging message a while after I've shut the furnace down by removing the door.
The nest thermostat is basically a computer. It can fail in many ways. By removing the W wore from the circuit board and the heat turned off means that everything in the furnace is working
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Customer reply replied 1 month ago
Nest ran all the tests and there's nothing wrong with the thermostat. The fan runs no matter what. The first tech had me switch the wires for the 24Vac, could that be the problem?
It may be that the 1-6 pins and the 3-4 pins need to both be jumped. I would use one of the other wiring harness to cut the wires and jump the 1-6 pin together like they are now and then also jump the 3-4 pins together like they were before.
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Customer reply replied 1 month ago
I'll give it a try. So you don't think switch the 24 Vac "x" wire with the common "c" wire could cause any problems?
No that would not cause the problem with the fan running but it may cause problems with the thermostat
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Customer reply replied 1 month ago
No change, fan still runs all the time. Switched the plugs on the Vac 24, no change. Like last night, when I started it up with the thermo down, just the fan. Turned the thermo up and the heat came on, turned the thermo down and fan kept running and heat did not shut off.
Customer reply replied 1 month ago
Switched the Vac/com plugs back to where they were and got the message that the Rh wire was getting no power. Put them back to where I had changed them to this morning and it went back to charging it's battery (all while the main power was on but the furnace switch was off). When the tech had me remove the w wire from the thermo, the fan kept running but no heat, so the W wires are connecting.
Customer reply replied 1 month ago
Switched the Vac/com plugs back to where they were and got the message that the Rh wire was getting no power. Put them back to where I had changed them to this morning and it went back to charging it's battery (all while the main power was on but the furnace switch was off). When the tech had me remove the w wire from the thermo, the fan kept running but no heat, so the W wires are connecting (but as noted, the heat keeps running once it starts, the thermo does not stop either the fan or the heat).
Customer reply replied 1 month ago
I note that when I open the furnace door to stop it from running, I once again get the message on the thermostat that the Rh is not getting power. I'm not sure if this was always the case.
Ok remove the nest thermostat from the sub base and see if it stays running. If it does then there is definitely a problem with the thermostat
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If it does turn off then the problem is with the thermostat if it stays running then there is probably a short in the wires.
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Customer reply replied 1 month ago
Okay. I put the front back on the furnace and the fan came on, but not the heat. I turned the thermostat up and the heat came on. I pulled the front off the Next and the furnace kept running and heating.
Customer reply replied 1 month ago
If there is a short, I would have to assume it's somewhere in the board I just installed. Where should I look?
Customer reply replied 1 month ago
Could it be that I just accidently crossed or misattached a wire or wires on the circuit board thermostat screws?
It would not be on the board. It would be on the thermostat wires. If you remove the W and G wires then nothing should run on the furnace
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Customer reply replied 1 month ago
During the nest checks, I removed several of the wires, switched them, etc. Nothing stopped the fan from running. It's late and Friday night, I'll chat with you tomorrow. I have an old thermostat that I could hook up and see if that works.

ok the next thing i would check is the limit switches in the furnace. it will require a meter to test them.

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Customer reply replied 1 month ago
Last message tonight, but what kind of a meter?
Customer reply replied 1 month ago
I've got one, you'll just need to tell me the settings.

OK JUST LET ME KNOW WHEN YOU ARE READY

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Customer reply replied 1 month ago
tomorrow 10ish pst.

ok

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Customer reply replied 1 month ago
Running late, it'll be a while. You can send me the settings anytime.

EVERY METER IS DIFFERENT AS FAR AS HOW TO SET IT BUT FIRST YOU ARE GOING TO WANT TO SET IT TO READ CONTINUITY AND TURN THE POWER OFF TO THE FURNACE AND TEST EACH SAFETY AND LIMIT SWITCH ONE BY ONE BY REMOVING THE WIRES AND MEASURING THE RESISTANCE ACROSS THE SWITCH. THEY SHOULD ALL HAVE CONTINUITY.

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Customer reply replied 1 month ago
I have my meter and am ready. I know of one limit switch (L150-30), but I am not sure what else I'm supposed to be checking.
Customer reply replied 1 month ago
I tested the L150F-30 With power off, clips off with 2 difference continuity checkers (on simple with light and one on my meter which registers and buzzes). No continuity. Now what?
Customer reply replied 1 month ago
I also tested it with my meter. At the lowest ohm reading (200), it registered 0.3 ohm. I believe it's supposed to register 0.0. If I assume that it's bad, would that explain the fact that the fan never shuts off and once it's started heating, it also doesn't stop heating?
Customer reply replied 1 month ago
where are these switches?

if you can take a picture of the upper compartment of the furnace I can highlight them for you to help you locate them

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the switches will be located behind the gas valve and on the top or side of the burners casing.

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Customer reply replied 1 month ago
You don't see them in either picture. Steer me in the direction of where I should look in the picture. Again the tests I ran on the limit switch don't mean anything?

I can not see them in the picture you provided. I will need to see what is behind the gas valve. the test you did on the limit switch earlier means that switch is good because it has continuity.

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Customer reply replied 1 month ago
You mean behind the blue box? If you do, I don't think there's anything behind there except the limit switch and that round thing on the left (but I'll double check).

yes. the round thing on the left is one of the limit switches too

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Customer reply replied 1 month ago
Okay,I'll do a continuity test on it. I'm a little confused on the limit switch I tested.
Customer reply replied 1 month ago
oop, meant to delete that last part.

ok also if you trace out the wires on those switches it will lead to any other limit switches too

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Customer reply replied 1 month ago
No light on the simple continuity tester, no reading at all on the meter on the round switch. (I redid the simple on the limit switch and is tested okay, not sure why it didn't the first time I checked it). I'll follow both sets of wires and see what I find.

ok just to clarify the larger black switch in the picture is a pressure switch not a limit switch and it should only have continuity when the fan s running. the limit switches will be smaller usually the size of a quarter.

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Customer reply replied 1 month ago
I was afraid you say something like that. Here's a picture of where the wires went to from the round (pressure) switch. If I have to check those, I'll have to take the whole side off of the furnace to get to them. I had difficulty following the wires from the limit switch you can't see. I think they go to the circuit board, but there is a second set of wires that go into the blue box. I typed this message before and it disappeared, so you may get it twice.

all of the limit switches will go to the blue gas valve. you can also check the continuity of the whole circuit by unplugging the connector and checking continuity of the two wires that go through the whole circuit

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Customer reply replied 1 month ago
do continuity testing with the wires coming out of the pressure switch and the wires coming out of the limit switch?

the wires going to the limit switches are a different circuit than the pressure switch. we want to test the limit circuit. follow the wiring diagram above for the correct wires

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Customer reply replied 1 month ago
I can only read simple schematics and that does not match my circuit board. I will try to follow the wires from the limit switch but I will have to cut the bundle free from the gas line. I assume you mean I can't just use the clips on the limit switch to do the testing. In which case what do I do the test on if the wires do go into the circuit board (plug)?

right now we are only concerned with the wires that go to the gas valve not the circuit boar which is only the upper half of the wiring diagram. it will be difficult to test from the plug with alligator clips. if your meter has pointy leads use those or clip the alligator clips to a small wire or paper clip and stick that into the plug terminals.

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Customer reply replied 1 month ago
You're still confusing me. What wires am I following (if not the wires from the limit switch)???

in the wiring diagram I circled the limit switches they are the brown an white wires on pin 1 and 5 on the gas valve. those are the wires we want to test right now

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Customer reply replied 1 month ago
I'll look, but I'm not sure where the C1 Plug is.

it is the biggest plug on the gas valve

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Customer reply replied 1 month ago
I'll look, but I'm not sure where the C1 Plug is. I think its in the bundle, which is so tight that I can't even move it. I'll cut it. Should I unplug the 1 and the five before I test. If so, test the wires or the socket? My meter has pointed tips.

the c1 plug is in the top of the gas valve. unplug it and test between the 2 pins.

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Customer reply replied 1 month ago
There is continuity. 0.3 on the meter and the light came on with the simple tester. I noticed one weird thing. On the thermostat, the wires are thus:
Yellow wire to Y, green wire to G, white wire to W and red wire to Rh.
However on the board the wires are thus:
Blue wire to Y, green wire to G, white wire to R, and red wire to W.
The blue wire is not connected at the thermostat. Could this be a problem.

IS THERE AIR CONDITIONING ON THE UNIT TOO?

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THERE MAY BE A SPLICE IN THE THERMOSTAT WIRE SOMEWHERE AND THE WIRE COLORS MAY CHANGE

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Customer reply replied 1 month ago
Maybe, both ends have all wires. Don't know how to check continuity at that distance. So what next?

DISCONECT ALL OF THE THERMOSTAT WIRES REMEBERING WHERE THEY WERE AND TURN THE FURNACE ON, IF THE BLOWER STILL RUNS THEN THERE IS A PROBLEM WITH THAT THERMOSTAT WIRING

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SORRY IF THE BLOWER DOESNT RUN THERE IS A PROBLEM WITH THE THERMOSTAT WIRING

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Customer reply replied 1 month ago
The blower runs.

OK THEN SOMETHING IS GOING ON WITH THE BOARD, EVERYTHING WE CHECKED LOOKS GOOD, THE REST OF THE TESTING WILL REQUIRE SOME ADVANCED SKILLS TO TEST. I WOULD RECOMEND HAVING A TECHNICHIAN COME OUT TO DIAGNOSE IT

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Customer reply replied 1 month ago
Thanks. Valiant effort. I'll get the tech back who looked at it before.

OK LET ME KNOW IF YOU HAVE ANY MORE QUESTIONS.

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I. Am trying to install a nest thermostat it is saying to check certain wires it was labeled with 2 letters I was told I had a heat pump is that dual fuel then and if so is it forced air? … read more
Billy
Billy
Journeyman Service Technician
State Licensed Mechanical Contractor
9,330 satisfied customers
I have a Weil mclain boiler, and a nest thermostat. the
I have a Weil mclain boiler, and a nest thermostat. … read more
Rick the plumber
Rick the plumber
Owner
9,857 satisfied customers
I have a NEST thermostat and for some reason it is not
Hi! I have a NEST thermostat and for some reason it is not turning on our air conditioner. I was trying to figure out if the problem is with the NEST or with the AC. … read more
Phil
Phil
Mechanical Engineer
Degree, Mech Engr Technology
6,938 satisfied customers
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Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

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