We have a Armstrong Ultra Sx80 furnace, model GUJ050D10-3A, with a HeatCraft Control Board, cat number 70k98 (40403001).

Everything fires up fine… thermostat, inducer motor/fan starts, then ignitor, gas, and the burners light, etc.
After the burners are lit for 30 seconds, the blower starts to turn on and then there are several rapid electronic clicking sounds from the control board, like maybe a switch or relay cycling on/off. Normally, I hear one click for the time relay to start the blower.
In this case, the blower never really stays on and eventually, the gas shuts off and the whole sequence starts over.
Sometimes, the blower stays on for a minute or two, then the relay/switch clicks rapidly and you can hear the blower start to cycle on/off.

If I let the furnace attempt to fire up repeatedly, the clicking sound then begins to occur when the inducer fan kicks on and then the firing sequence never begins, as I would expect. But mostly, it gets through the fire sequence and then the blower nevers fully comes on.

Could one of more time delay relays on the control board be faulty?
When wiggling some of the wires to the control board, the switching sound occurs rapidly as the blower attempts to turn. I checked the voltage from the 24V transformer to the control board and its putting out ~28V, seems to be OK.
I removed all the wiring spade connectors to the board and checked them for damage/corrosion, they appear fine. Re-attached the wires and it ran fine for a day, then this started again.

It would appear to be a faulty control board?
I either want to replace it myself or at least have this knowledge when a tech shows up.

Can someone help?

Thanks in advance. Jason

[quote=jsmith777;1403027]We have a Armstrong Ultra Sx80 furnace, model GUJ050D10-3A, with a HeatCraft Control Board, cat number 70k98 (40403001).

Everything fires up fine… thermostat, inducer motor/fan starts, then ignitor, gas, and the burners light, etc.
After the burners are lit for 30 seconds, the blower starts to turn on and then there are several rapid electronic clicking sounds from the control board, like maybe a switch or relay cycling on/off. Normally, I hear one click for the time relay to start the blower.
In this case, the blower never really stays on and eventually, the gas shuts off and the whole sequence starts over.
Sometimes, the blower stays on for a minute or two, then the relay/switch clicks rapidly and you can hear the blower start to cycle on/off.



Clean the flame sensor first then post back.

I cleaned the flame sensor and then re-started the furnace. At this point, the control board clicked incessantly after the thermostat kicked on and the inducer motor would not fully start, no ignitor, flame, or anything.
Does this make any sense why this would happen from cleaning the flame sensor?

I played around with wiggling the wires going into the board, just moving them around in general. I probably could have tried to isolate which wires, but it really didn't seem to make sense.
I then looosened the 4 mounting screws holding the board and then re-tightened. At this point, everything kicked on and worked OK.
I did the same thing a few days ago and it worked for about a day, then stopped.

It doesn't seem to make any sense that wiggling some wires around and re-seating the board would fix this.
I guess I use a multimeter to check for wire continuity from each furnace component to the board.
Any thoughts?

Same thing happened again a few hours later.
Clicking noise from board as main blower starts, but flame and blowers are going full.

After a few repeated attempts, the clicking noise from the control board begins as soon as the Inducer fan turns on, and the ignition never begins.

I would check the hot leg,neutral,and ground from the house panel all the way to the furnace disconnect/off-on switch and from there into the furnace. At that point make sure all hot,neutrals and grounds age good in the unit.

The electronics in the modern day furnace are very sensitive to loose/bad biring.

Try jumpering the heat contacts in the furnace to eliminate the thermostat control.
See if that has positive result.

The next step you have to becareful and mark down all wiring and where it goes on the circuit board.

Remove circuit board from unit and check for bad solder joints. This is a known problem on some circuit boards.

Neutral to ground = 0
hot to ground =120V
hot to neutral = 120V

Jumpered R to W for the thermostat, but the problem was not corrected.

Inspected all the solder joints and nothing appears out of the ordinary as I can tell.

There is one resistor (R1) on the control board which has some browning on both ends of the board, but the circuit is not open.

But now as soon as the inducer fan comes on, the control board clicks several times and the inducer fan shuts off or does't even start, even before it tries to pull vaccumm on the pressure switch.

Any other things I can try?

Thanks for any suggestions.

I hate to say this but the circuit board controls all the happening with that unit. If it is not a bad ground then it could be out of phase if you switched the transformer leads for the voltage in or out of the transformer since many of the circuit boards are very sensitive to this. Is it tossing a code on the board light? If so look at the code schedule on the drawing on the back of the blower door and post what it is. Other than that it might be circuit board time.

Now I am sure you tested all the components like the igntor etc.

This older style HeatCraft board does not have any Diagnostic LEDs :(

Last night it actually ran fine but all the while the control board was clicking incessantly as the main blower was running. Nothing ever shut off until the t-stat reached temp. I let it run that way for awhile and then it got progressively worse.

The problem seems to come and go as the furnace as been running for awhile, but eventually the inducing never kicks on. Kind of frustrating because its hard to isolate.
Guess I look into a new control board.

Thanks for all the helpful tips.

I replaced the control board, though it wasn't cheap ~$180.
The furnace has worked perfectly since.
Since the furnace would work fine sometimes, I believe a bad relay or relays on the control caused the intermittent performance.

Thanks for the help and the tips in order to do this myself.

Glad you got it running.

Had the same problem... with same R1 resistor showing overheat.
I corrected the problem with a new control board.

Same problem here, but in my case I got lucky and just had to tighten the 4 screws that held down the board. They were very lose and the lack of a good ground was causing my problems.

Well it didn't last very long. Had to go for the new control board too.

Since I have an identical furnace for the 2nd floor, I think I'm going to try replacing R1 (burnt looking) and when that furnace acts up replace the control board with this "repaired" one.

The ultra sx 80 furance does not turn on if i disconnect a connector ( not the presurer switch)that goes into the back of furance it will kick on both fans i repace the connector than the ignitor would click a flame on for a couple second turn off. Fan will turn off also.

This answer is a few years late, but I wanted to say I had the same furnace, and the same problem just occurred last month. I saw the same browning around a certain resistor on the circuit board. Instead of replacing the board, I took it off, and noticed that the solder joints on that particular resistor were loose (I guess it was arcing on the solder joints, that explains the browning). We re-soldered it and the board has been working fine for about a month now.

Had the same problem, and was able to find a solder joint on the board that didn't look quite right. Re-soldered, and haven't had a problem for 3 years.

I just finished with mine... removed the board and inspected it. I found numerous 'cold-solder' joints on the back of the board on the terminal mounts. I resoldered these and reinstalled. It's been working fine since.
I expect the board was assembled poorly.
Good Luck!