Furnace won't open gas valve - possible control board issue?

lizardrock11

We have 2 American Standard Freedom 80 furnaces, model ADD080R936E0. One of them is refusing to turn on. When the thermostat calls for heat, the status light indicates a call for heat, the flue draft blower comes on, and the ignitor glows bright orange. After about 10 seconds, the ignitor shuts off but the blower does not come on. After about 45 seconds, the cycle stops and starts again. After 2 tries, I get the error code “External lockout (retries or recycles exceeded)”.

When I start the other furnace, after the 10 seconds of flue draft blower and ignitor glowing, I hear a loud click from the control board and the burner ignites.

I think our control board in the bad furnace isn’t sending voltage to the gas valve and should be replaced but would love some advice if this sounds like the likely cause of the problem.

Thanks!

EBEBRATT-Ed

When the inducer blower turns on there is a pressure switch inside the furnace that "proves" that the inducer blower is running (you don't want the gas to fire if the inducer isn't running")

First step is to check the pressure switch with the inducer running to see if the pressure switch contacts are closing.

But first disconnect the tubing running from the pressure switch and blow it out to make sure it is clean. There may be 1 or 2 tubes. After blowing it out reconnect the tubing and try and start the furnace. Also check the furnace flue and air intake to make sure they are clear

If the pressure switch works then you move on to the gas valve and or control board

lizardrock11

Thanks. I'll check that.

HVACNUT

Use the money you were going to spend on a board and get an electric meter that can also read resistance. It could be as simple as a tripped limit due to a dirty air filter. Or it could be the board. Or rollout, or spill switch, or pressure switch, or gas valve, or...

motoguy128

Is there a fault code flashing on the control board?   If the ignitor comes on the pressure switch is usually closed.  But on some older furnaces the pressure switches only interrupt the gas valve.  

That wing said You need to check to see if the gas valve gets 24vac to open.  You need a volt meter to check this.  You also should normally hear and feel and slight click from the solinoid in gas valve.  

If you have voltage but valve  isn’t opening, the valve is most likely bad. It will need a like replacement.  

If it is not getting 24vac then follow the wire and check for switches in series or a loose connection.  But in that car,  it’s most likely a bad board.  

Most replacement Trane boards are upgrade kits and come with a new ignitor.  Not too wow side.  

lizardrock11

The pressure switch checks out fine. It closes when the inducer blower comes on. I have to figure out which wires on the gas valve to check for voltage, but the big clue is that the good furnace (same model) has a loud click from the control board when the burner lights but the bad one is totally silent. I'm betting on a bad control board, but want to be sure before I spend $240 on a control board.

pecmsg

Break out the wiring diagram and see what other safety’s are in line with that limit. 

Seabee5701

Checking voltage at gas is good move. Usually a plug end connects to gas valve. Meter needed like others say. It is very possible that the igniter is bad. Wouldnt hurt to get one and try it. 

JUGHNE

If identical boards, just trade them out and see if the problem follows the board or stays with the furnace.

HVACNUT

JUGHNE said:

If identical boards, just trade them out and see if the problem follows the board or stays with the furnace.

That's cheating. 

JUGHNE

Yea, that's right....maybe.
But you don't let the homeowner realize that is what you are doing. You just explain that, being how I'm here I thought I should check out your other unit.....no extra charge, mind you.

EBEBRATT-Ed

That will work hope the furnace doesn't have a shorted gas valve

mattmia2

EBEBRATT-Ed said:

That will work hope the furnace doesn't have a shorted gas valve

you could put the suspect board in the working furnace

JUGHNE

Yes ED, that is possible.
But forgetting that the OP does not have volt meter, I would have looked for 24 VAC at the GV.
Shorted GV probably would have blown 3 amp fuse.....if it had one.

Seabee5701

Why look beyond the ignitor???? It is acting as if the ignitor is not getting hot enough...if it doesn't, it will try for  ignition a few times then lock out..thats exactly what is happening ...please just  replace the ignitor and dont worry about the gas valve  or circuit   board....

JUGHNE

I don't think the board knows if the ignitor is hot enough.
But it will try to turn the gas valve and then immediately look for the fire, if no fire then shuts down gas valve within seconds.
May then retry 2 more times.

On most furnaces I have seen, if any limit is open the lighting sequence will not even begin. Just the inducer fan and sometimes the main air blower runs.

Seabee5701

I think it has to sense a small amount of amperage.....and that goes back to the board. If its worn/old it doesnt heat up and generate amperage.....

HVACNUT

Typically, the gas valve circuit will go through its sequence (electric ignition) regardless of what the ignition circuit is doing. As long as everything is closed, the valve should get 24v. Even if the HSI wasn't working (which it apparently is working) the gas valve will still receive 24v during trial for ignition. 
Just buy a *$#@! meter.

EdTheHeaterMan

According to the Service Facts for this model, there are 2 fusable links that are a one-time (not resettable) safety switch that may fail when there is an over-temperature condition in the fire-box or burner-box area. I would usually call then "Roll Out Fuses" If one or both of these were open, this would explain your condition and 2 blink error code. There are also 2 other limits on the same circuit that are automatic reset. They are connected with yellow wires of if all the wires are the same color (A normal thing with Trane and AS) then the wires are identified as " YL "and "YL/1", "YL/2", "YL/3' and so on.

Did you get a METER yet?

EdTheHeaterMan

lizardrock11 said:

The pressure switch checks out fine. It closes when the inducer blower comes on. I have to figure out which wires on the gas valve to check for voltage, but the big clue is that the good furnace (same model) has a loud click from the control board when the burner lights but the bad one is totally silent. I'm betting on a bad control board, but want to be sure before I spend $240 on a control board.

I'm going to say it again: After you replace the control board and it does the same thing, what will you check next? If that is less expensive then check it first.

I'm not sure if this link is password protected but this might be a paper that came with your furnace.
http://literature.ingersollrand.com/WEBCACHE/B-439-253_08011992.PDF

I can't find the one with the ADD080R936E0

only the *DD080R936A

mattmia2

The control board would be my last suspect for a condition like this. i would only consider it after checking everything feeding information in to the control board.

mattmia2

Perhaps something is wrong with the flame sensor such that it immediately knows it is not proving flame like it is shorted.

Seabee5701

Its the ignitor.........

JUGHNE

Being how you have a set of twins, a spare ignitor would not be a bad idea, it is just about the least expensive part that has been mentioned.....and often the first to fail.

So please replace only that part and report back.
Maybe Seabee is on to something!