Ignition control module or gas valve

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Old 01-20-19, 07:37 PM
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Ignition control module or gas valve

I had an Amana Air Command 90 gas furnace (model GUC 070B30B) installed in my home Oct. 1990. Serial number is 9007073863. At the beginning of this winter (last Oct or Nov) I replaced the original draft inducer blower motor with a new one - Fasco A189 1/24 HP 115 Volt 3000 RPM Goodman Furnace Draft Inducer Blower. The furnace was working fine, but one day I heard what sounded like water gurgling in the exhaust pipe, and I realized the condenser pump had stopped working. I opened the lower outlet of the inducer blower and a lot of water poured out. After letting the inducer blower drain of water, I turned the furnace back on and it went back to working properly. I ordered a new condenser pump - Little Giant VCMA-20 (model-20ULS). Before the pump arrived, I check the inducer blower every couple of days to make sure any condensation was drained away.

In addition, before the pump arrived, a previously scheduled duct cleaning service came to my home to clean out all my duct work and my furnace. The technician cut an "access panel" in my duct work directly above the furnace in order to insert their large vacuum hose. After the cleaning, while the technician was packing up hoses and vacuum lines, he was running the furnace to make sure everything was operational. When he left, at about noon on a Thursday 2 weeks ago, the furnace was working. When I returned home from work Friday evening, the furnace was not working but the inducer motor was running and was very hot. I shut off the electricity to the furnace to stop the inducer motor and allow it to cool. My furnace has not run since then.

I managed to get the owner of the duct cleaning service to come back out and inspect my furnace to make sure his technician had not done something to cause the furnace to stop working (like, possibly, getting metal debris into the burner area when cutting the access panel). We could find no evidence of that. But he did notice that my hot surface igniter didn't appear to be getting hot enough, so he recommended changing out that part. I purchased a new White Rodgers Ignitor - 767A-369 - and installed it, but the furnace still didn't work.

In installed the new condensation pump, but that made no difference. The furnace still doesn't work.

So I've come down to either the problem being either in the ignition control module or the gas valve. The currently installed control module is a White Rodgers Universal Hot Surface Ignition Control - Model 50E47-843. The gas valve is a Goodman C6423501 model.

Is this gas valve supposed to receive 24V from the ignition control module, or should it be in the millivolt range? I'm reading about 900 mV during the time period, after the hot surface igniter has been glowing for several seconds, when the gas valve is supposed to open and feed gas to the burners.

Also, I purchased a new gas valve from Grainger that's supposed to be a replacement from the now discontinued Goodman valve. The valve I purchased is a Robershaw 720-079 Universal Electronic Ignition Gas Valve Uni-Kit. Is this the correct replacement for the Goodman valve?
 
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Old 01-20-19, 07:43 PM
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I should have mentioned that the entire startup sequence seems to work properly except that no gas is delivered to the burners. First, the inducer motor comes on. After a minute or two, the hot surface igniter starts to glow. But the gas is never delivered to start the burners.
 
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Old 01-20-19, 09:10 PM
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Everything follows a logical timed order....
Call for heat.
Inducer starts up and start pre-purge
Pressure switch proves and igniter starts to heat.
After igniter warmup.... 30-45 seconds.... the gas valve opens.
If there is no flame detected the gas valve closes and the igniter shuts off.
Inducer still runs.
After post-purge..... 30-60 seconds..... the cycle starts over.
After three attempts the furnace should go into lockout.

Some older furnaces follow a slightly different pattern but if the burner doesn't light.... the igniter must shut down.
The gas valve only gets 24vAC power for approx 7 seconds before igniter shuts off.

You should put a voltmeter directly on the gas valve terminals. It must be connected. If you don't see 24vAC for +/- 7 seconds then the controller has a problem.
 
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Old 01-21-19, 11:18 AM
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Thank you, Pete.
My furnace turn on sequence follows the order you've detailed here . . . except that only the ignition controller goes into lockout after three tries. The inducer continues to run.
I think I've tested the gas valve correctly - touching the voltmeter leads directly to the gas valve terminals. But I'm getting only 300 mV from the controller for the 3-4 seconds it's supposed to open the gas valve.
 
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Old 01-21-19, 12:30 PM
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At the moment when you should get 24v on the gas valve..... the module should click as a relay closes for power. My guess is that relay is defective and you'll need a new module.
 
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Old 01-21-19, 11:16 PM
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Found the problem but can't identify device

24V is being delivered from the ignition control module to the device I've attached a picture of. The 24V is not passing through this device to get to the gas valve. Can anyone tell me what this device is and why it is in the line that goes from the ignition controller to the gas valve. Is it some kind of voltage regulator, or a capacitor perhaps?

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Last edited by PJmax; 01-21-19 at 11:47 PM. Reason: resized picture
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Old 01-21-19, 11:57 PM
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That's a high limit safety switch. I was able to find a manual for your furnace. That part is called the primary rollout limit switch. That means it's mounted outside and just above the burner area. That part will interrupt power to the burner (gas valve) when it senses too much heat caused by overfiring or possible plugged exhaust flue. I believe that is a 180 degree limit. Can't tell if that's a resettable one where the button pushes in. See if there are any numbers on it.

Download the manula for your reference... Amana *UC manual (pdf)
 
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Old 01-22-19, 12:21 PM
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Thank you, Pete. You're correct. It was mounted behind the gas valve and just above the burner area. I did a voltmeter test of the line going into it to be sure it was receiving 24 volts; then tested the line coming out at the gas valve and it measured only 300 mV during the sequence where it should have delivered 24 volts. So I took the limit switch out before realizing that it has a button on it that might have allowed me to reset it. I'm at work now, so won't be able to reinstall it and test it again until this evening. But I'm going to try to find a replacement for it in the meantime.
 
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Old 01-22-19, 01:03 PM
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By the way, you mentioned that you thought this is a 180 degree limit switch. Did you get that from the table on page 47 of the manual you linked to? (Intersection of second column and second row?)

On page 57 of the manual, in the instructions under "S-24 Checking Flame Rollout Switch" it looks like my GUC070 uses a 350 degree switch. That makes more sense to me, for a switch sitting right above the burners. 180 degrees seems to be too low for the location. Would you agree with that?
 

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Old 01-22-19, 07:06 PM
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Yes.... 180 would be low there. I've been having trouble locating the correct part.
I come up with 10123503 which is 300 degrees.
Amana/Goodman Limit
 
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Old 02-07-19, 08:21 PM
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Pete,
I purchased a Grainger limit rollout, manual reset switch (http://************/yd8earh8) and installed it a couple of weeks ago. Since then the furnace has worked, but not the way I was accustomed to. Every now and again the furnace will go through it's startup sequence, the burners will light, and the warm air will be blown through the house. After the house has warmed to the thermostat setting, the furnace cuts off. But a couple of minutes later the fan motor will come on again for about 20 seconds and then shut off. It seems as though the furnace has decided, "Hmmm, I didn't get all the warm air out of my ducts, so let me give a 20 second blow to clear them." Do you have any idea why this might be happening?

In addition, there have been two times, since I installed the rollout switch, that the furnace has stopped working. Each time I've had to shut off the power, press the manual reset of the switch, and restart the furnace. The last time this happened was last night, in the middle of the night. The ignition module was blinking a red "lockout" signal, and the inducer blower motor was running. I don't know how long the inducer motor had been running, but it was pretty hot to the touch. I let it cool down, pressed the manual restart of the rollout limit switch, and restarted the furnace. It seems to be running okay now, but it's still doing the 20 second blow a few minutes after the normal warming period has ended.

Do you think I may have purchased a faulty rollout switch?

Any insights you could give me would be much appreciated.
 
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Old 02-07-19, 10:07 PM
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Ok....... you've got something serious going on there. If that rollout switch is tripping...... your furnace is running too hot. Since it's running hotter than normal..... the standard timed cool down period is not long enough and the high limit sensor is opening which will cause the blower to run until it re-closes.

This type of trouble is very hard to diagnose thru the internet. I'd recommend calling your gas provider and have them send a tech to check it out. Usually those guys are well trained and fair. They won't try to sell you a furnace unless it's really needed.
 
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Old 02-08-19, 05:38 PM
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Thanks, Pete. I'll try that.
 
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