Gas Furnace Repeating Mid-cycle Shutdown Mystery (No Lock-out,No Error Code)-Watch Vids

armstrongahhh

Hello everyone - needing some help here. I have an Armstrong Air HE furnace that has stopped working. It starts out fine but shuts down after the igniter glows for like 20 secs (no flames). There also seems to be a click sound right before it shuts off. It will then restart the process and keep trying with the same mid-cycle shutdowns - no lock-out or error codes. A short vid of what's happening:

https://workdrive.zohoexternal.com/f...242b9c75b84205

So far I have tried:

1. jumping R and W on the thermostat and no change.
2. jumping R and W on the furnace control board and getting consistent 28V between C and W
3. testing gas valve voltage (wires disconnected): it started at 14V and went up to 28V when the valve was being energized. It then however dropped to 15V right around when the soft click sound happened.

https://workdrive.zohoexternal.com/file/76fn20923a26a705f4d6f8e92ef0cc1f4a962

4. testing gas valve voltage (wires still connected): readings were steady at 0.2v/0.3v before reaching 0.8V when the valve was supposed to open (read somewhere readings may not be accurate with wires still connected?); they were somewhat lower than another identical working furnace that started out with about 1V and then jumped to 27/28V once the flames came on.

Here's the expected Sequence of Operation:
1. When thermostat calls for heat, combustion air inducer starts.
2. Combustion air pressure switch proves blower operation. Switch is factory set and requires no adjustment.
3. After a 15 second pre-purge, the hot surface ignitor energizes.
4. After a 20 second ignitor warm-up period, the gas valve solenoid opens. A 4-second “Trial for Ignition” period begins.
5. Gas is ignited, flame sensor proves the flame, and the combustion process continues.
6. If flame is not detected after first ignition trial, the ignition control will repeat steps 3 and 4 four more times before locking out the gas valve. The ignition control will then automatically repeat steps 1 through 6 after 60 minutes. To interrupt the 60 minute period, move thermostat from “Heat” to “OFF” then back to “Heat”. Heating sequence then restarts at step 1.

Feels like something goes wrong in Step 4.
Also it does not go into a lock-out after letting it run (and fail) a few times if that means anything, and no error code.

The help I have got so far suggests it could be the board and/or the valve:

Board: It does not go into a lock-out or give an error code

Valve: it doesn't seem to open when it's time to do so despite getting the right current (28V); it then drops (with the click) which could also indicate a bad valve (?)

I would really appreciate it if you could help identify possible issues/causes, or advise any test that can help diagnose the issue. Thank you.

HVACNUT

You get 24 volts across Orange and Yellow with the wires disconnected from the gas valve, but .8 volts when they are connected to the gad valve?

Ohm out the gas valve.

I also don't believe it's code to have a union inside the cabinet.

Jamie Hall

And before you start throwing parts at it — that voltage drop when the gas valve is connected suggests very strongly to me one of two possibilities. One is cheap — so check that first. Specifically check every single connection from the transformer through and connectors to the valve for cleanliness and security, and do exactly the same going back through ground and any return wires. You have a huge voltage drop in there somewhere, and the likely culprit is a bad connection (or even a broken wire). The other is that the gas valve is shorted — but that should blow a fuse…

armstrongahhh

https://forum.heatinghelp.com/discussion/comment/1811064#Comment_1811064

I ohmed it previously (with everything off and wires still connected to the valve) and the reading was 0.5 (on 200 ohm band). I then read that some valves cannot be ohmed corrected because of some internal electronics in them and ohming it may also damage it (?)

armstrongahhh

https://forum.heatinghelp.com/discussion/comment/1811077#Comment_1811077

Thanks Jamie. I wouldn't want to throw parts, ie $$ either; just it seems this is not going anywhere. I checked the wires and connections before and they looked okay, e.g. I did unplug, check and then unplug the molex connector. Now with me new to this, the check may not be thorough/correct.

And one other thing I noticed (in the 2nd vid) is that there was a click in the valve and immediately the voltage went up to 28V, then came down (this may be because the board was shutting things down as no valve was connected). Besides the 1st one, there were a couple more light click sounds; I now wonder where they came from; shouldn't be from inside the valve as it was disconnected and should not respond to the 28V. By comparison, I can hear a louder sound at the shutdown in the 1st vid, no clicking, when the valve was connected normally.

Jamie Hall

0.5 ohms sounds low to me. I'd expect a higher reading. Without going through the whole circuit diagram, I'm not sure where to check next — but that low a resistance on the valve will draw too much current from the transformer and that may be shutting everything down.

armstrongahhh

https://forum.heatinghelp.com/discussion/comment/1811086#Comment_1811086

Someone else mentioned that possibility as well; would a working board flash an error code in this case, or it's furnace dependent?

The 0.5 ohms may also because the wires were also attached that may give rise to inaccurate readings?

I also updated my last reply re the clicking sound by the way after re-watching both vids. My apologies for the confusion.

mattmia2

Can you take a picture of the schematic? is there a safety between the ignition control and the valve?
The dc resistance of an ac solenoid is hard to predict. A better test would be to first measure the voltage at the terminals of the ignition control then put an ac ammeter in series and measure the current.

mattmia2

Do you know you have gas to the appliance? Check the voltage at the transformer and the supply to the appliance to make sure there isn't a bad connection somewhere in there causing power to drop when it switches the valve on.

armstrongahhh

Hi sorry @mattmia2 for the late reply. I didn’t receive an email notification of your comments and is just checking this now.

I’m not familiar with the ignition control; is it part of the board? The valve is connected to the board by 2 wires through a molex connector:

There’s gas to the unit as another identical unit next to this one works fine.

I found https://www.youtube.com/watch?v=1JWZjLp-mwI

The issue described there looks very similar to mine. It was identified as a shorted gas valve.

Following his steps, i ohmed out the valves on both units and the good valve read OL and the bad one 1.0. So looks like it’s the valve. Let me know your thoughts please.

Re no lockout-out/error codes - I believe it’s because this specific board doesn’t capture a shorted/faulty valve at least not before the flame comes on, based on the error code list:

CODE: 1 Flash

RESULT: Flame present with gas valve off.

CODE: 2 Flashes

RESULT: Pressure switch closed with inducer off.

CODE: 3 Flashes

RESULT: Pressure switch open with inducer on.

CODE: 4 Flashes

RESULT: High limit switch open.

CODE: 5 Flashes

RESULT: Rollout switch open.

CODE: 6 Flashes

RESULT: Pressure switch cycle lockout.

CODE: 7 Flashes

RESULT: Lockout due to no ignition.

CODE: 8 Flashes

RESULT: Lockout due to too many flame dropouts.

CODE: 9 Flashes

RESULT: Incorrect line voltage phasing.

mattmia2

@armstrongahhh the shorted gas vale would be 6 or 7 but if it is dropping the 24vac supply then it is resetting the board.

If you click the ribbon icon at the upper right of this top of this post it will turn on notifications.

Put an ammeter in series with the gas valve, start with the high shunt, 10a or 20a or whatever it is and move down if that seems normal. The valve shouldn't be open unless the switch is off unless there are electronics inside it. the ammeter is the best way to see if it is drawing the correct current. A bad connection could be causing the voltage to the control to drop as soon as the gas valve opens too.

armstrongahhh

Thanks @mattmia2! Didn’t know I need to click the ribbon; i thought I’d get notified automatically as the OP. Just subscribed.

Re the ammeter testing - is it the same as #3 in the OP:

3. testing gas valve voltage (wires disconnected): it started at 14V and went up to 28V when the valve was being energized. It then however dropped to 15V right around when the soft click sound happened.

https://workdrive.zohoexternal.com/file/76fn20923a26a705f4d6f8e92ef0cc1f4a962

Also is an ammeter the same as a multimeter on VAC?

Sorry about all the questions; new to the hvac world and trying to learn.

mattmia2

No. An ammeter measures current, the amount of electricity flowing. A voltmeter measures potential difference between 2 points, basically the force trying to make current flow.

To measure current you would disconnect one of the wires to the valve and connect one lead of the meter to that wire and the other lead to the terminal on the valve you unplugged it from. You need to set the meter to ac current ("ac amps") and on most meters you need to move one of the leads to a different terminal on the meter. I would use the 10a or 20a range, whatever range your meter has.

The ammeter gets connected in series with the load to measure the flow of electricity.

BE SURE TO PUT THE PROBES BACK TO THE NORMAL POSITION ON THE METER AFTER YOU ARE DONE BECAUSE THE CURRENT MEASURE SETUP OF THE METER WILL SHORT ANY VOLTAGE SOURCE YOU TRY TO CONNECT IT TO.

armstrongahhh

https://workdrive.zohoexternal.com/file/n3mie0f450d076b3d4dbb8c84d68399989607

i appreciate the detailed instructions @mattmia2! I was able to follow along and it went up briefly to around 1.5A when the valve was energized.

mattmia2

Does it stay there or does it drop down before it turns off? what does it say on the valve? They are usually more like .25 a.

mattmia2

Measure the voltage at the transformer when that happens. Either the valve is shorted or there is a bad connection where 24vac comes in to the control. Make sure the pins in that molex are all seated in the housing, sometimes one will get loose and push out instead of plugging in. I think the yellow and blue are from the transformer, i would look at the other side of the board at that connector for bad solder joints.

armstrongahhh

it went up to 1A just when the igniter started to fade, and gradually dropped down immediately after to 0. The link in my post was a vid of what happened.

https://workdrive.zohoexternal.com/file/n3mie0f450d076b3d4dbb8c84d68399989607

armstrongahhh

Thanks; will check the transformer voltage and solder points at the back of the board. They may take me some time to do as I will first need to look into the how-tos. Will report back once done.

armstrongahhh

I didn’t find specific info on testing transformer voltage unfortunately. Is the plastic squash (marked by LINE and LOAD, pointed by the red arrow in the pic) the transformer? transformers I saw online had a metal casing so wanted to double check.
re the test - do I just put the multimeter probes on the blue and yellow metal terminals (in yellow circles) of the transformer while the furnace is trying to run?

Also the molex pins looked okay and I tried pushing the wires in a bit more to ensure good contact; didn’t feel any was loose:

Blue circle: gas valve wires

Red circle: transformer(?) wires

mattmia2

The metal square with the plastic insulator and the quick connect terminals is the transformer. Measure the voltage on the yellow and blue wire while the furnace tries to run and see if it drops when the gas valve tries to open. If it does it is probably a shorted gas valve.

armstrongahhh

Thanks for confirming @mattmia2. It was steady at 28V and dipped to about 25V very briefly (1-2s) when the shutdown began (with the click sound). It then came back up to 28V almost immediately. Wasn’t able to hold the meter in the same view sorry as I needed to hold a few things including the probes (with tiny metal leads) onto the terminals; hope the click at the end/shutdown provide some context. Does this implicate a shorted valve?

https://workdrive.zohoexternal.com/file/sppu046c9f8a2286e413b96c736d7356953df