My Goodman GHS80905CNA furnace that was installed as new construction in 2006 will not light. When called for heat the inducer motor runs for a few minutes then turns off. The circuit board error code shows three flashing red lights.

Based on the guidance of other users posts, I have cleaned out the inducer pressure switch connector and the rubber hose. I have also tested the pressure switch by manually (sucking) the switch open and closed with no issue and voltage tested to ensure that the switch wasn't stuck closed. With the rubber hosed detached from the inducer blower (while running), the pressure switch contacts read 26.1 and 0.01 (open), then with the rubber hose reattached the contacts read 26.1 and 26.1 (closed). I believe this confirms that the inducer blower and pressure switch are okay.

At this point I'm stuck as to what to try next. Could it be that the gas is running but the lighting element isn't working? The lighting element is definitely not lighting up. How do I test the lighting element? How can I tell if gas is running?

Why would I get the 3 blink error code if the pressure switch appears to be working? I read somewhere that inducer blower also has an internal sensor to ensure the fan is spinning. Is it possible that the inducer motor can appear to be running from the outside (spinning), but the internal fan blades are seized? But, wouldn't this stop the pressure switch from closing, which is not the case.

Any help, guidance, advice is greatly appreciated.

Thanks,
Sideshow76

 

Also, just tested the primary high limit switch and the two manual limit reset switches, and they were all 27 VAC on both sides of the switch with the system calling for heat and the inducer motor running. Does this rules these switches out as the cause?

 

Yes.... the pressure switch appears to be working because it is working. It is not seeing the correct vacuum so it's not switching.

The biggest problem on the Goodmans is a clogged nipple where the rubber hose connects to the draft inducer blower. It usually takes a small drill bit to clean the hole out. Maybe a 1/16" bit. The tiny hole gets rusted over.

 

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That's very good troubleshooting! (The only exception, sucking on pressure switches is not recommended. Your test with the hose connected and disconnected verifies that the pressure switch is not the problem)

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Yes, that's the next thing to check. An ignitor that has burned out will USUALLY have a visible crack in it, often outlined with a whitish powder.

If the crack isn't visible, use an ohmmeter to check for continuity through the ignitor.

If the ignitor checks out OK, the circuit board could be failing to turn on the 120 VAC to heat up the ignitor. Connect your multimeter across the wires powering the inducer motor and see if you get 120 VAC being switched on after the inducer motor comes up to speed and the pressure switch closes.

It's MUCH more common for the ignitor to fail, so check that first.

If it's bad, buy two, with one as a spare for the next time.

 

I tested the ignitor for resistance and got 58 ohms. I then tested the wires going to the ignitor for voltage with the call for heat/inducer motor running and there was not any voltage reading on either wire (black/white). So it appears that the system is not signaling the ignitor to heat up. What could cause this?

I also tested the voltage going to the inducer motor and its 125 volts. I'm still getting 3 flashing lights.

Thanks for all of your assistance. Looking forward to getting this mystery solved!

 

Did you read my reply ? You've proven that the pressure switch itself is working. However.... the pressure switch requires vacuum to switch which your furnace IS NOT supplying it.

If the pressure switch does not close.... you will not get gas flow or the igniter heating.

 

PJ, thanksyou for your help. I have voltage tested both terminals on the pressure switch with the inducer blower running and they both read 27 volts. Doesn't this mean that the pressure switch is working properly with sufficient suction in the closed position?

 

It seems like the control board is going into error mode too quickly. It starts the 3 blink error within 3 to 5 seconds of starting the inducer motor. Is it possible that the control board just needs to be reset somehow to clear an old stored error code?

 

Pete has asked you several times to clear the nipple on the inducer blower. Have you done so?

The way your furnace works, you must first have proper vacuum to pull in the vacuum switch. Then the igniter will glow. Next, the gas will turn on and the burners should light.

After you clear the nipple, check for a larger hose off of the inducer housing. if you have one, check it for water (condensate) backup. Clean and drain it if there is water.

 

One of the terminals of the pressure switch will have 24v on it at all times. The other terminal goes to 24v as soon as inducer starts.... or within a few seconds..... watch and see how long it takes until this terminal goes high.

The control board is reset every time power is turned off.

 

Per my initial post, reaming/cleaning/clearing the nipple connector and rubber hose was the first thing I did. My unit is an 80% efficiency unit so it doesn't have a condensate line running from the inducer, only a suction line to the pressure switch. I have also confirmed using a voltmeter to test both connections on the pressure switch while the inducer motor is running that the pressure switch circuit is open when the suction hose is detached and and closed when the suction hose is attached.

I believe the volt test confirms that the pressure switch is working properly and that the issue is not a suction/pressure switch issue. Correct?

Thanks for your help.

 

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Yes.

 

Ends up it needed a new control board. $52 + 10 minutes = problem solved. Thanks for everyone's input and help!!

 

You guys are the men but I feel like THE MAN! Y'all saved me a service call. Cleared the nipple on the blower motor and I have heat

 

Welcome to the forums. Good job.

 

can you blow compressed air into the motor housing nipple to clean it out, what is on the hidden side of it, is there a screen to keep dirt out of the pressure switch tube ???

 

I would pull the drain line off the housing and see if you get any water or gunk out of it.

 

Thanks so much for your response!
I pulled the pressure switch and blew in and out of the tube, the switch activates when i do this, it tests working, and all looks brand new.

After I did this the furnace has worked without fail for a day, But I would like to make sure there is nothing blocking the nipple on the inside of the IDM housing. but I am not sure what the port is on the hidden side inside the housing. Is there a screen or is it just a hole, I dont want to damage anything if I use a toothpick or compressed air.

 

I guess someone would have had to replace the idm housing to know what the back of the port/nipple looks like. Finding someone with that kind of knowledge and experience would probably be next to impossible. I suppose i will just have to take a chance with it.

 

Don't use compressed air on the switch. I would use a paper clip and push (lightly) into the nipple. What kind of problems are you having?

 

I have a random issue that shows up 50 times a day or could be once every three weeks. Very intermittant.

The burners kick off and the fan continues to blow until thermostat is reset.

I have replaced: the roll out, flame sensor, thermostat, fan logic board, and high limit switch.

I have cleaned: the filter, all airflow passages, induction stack.

I have tested: thermostat wires, most connections, grounding to breaker.

Been working on this for 3 months.

 

I don't intend to use compressed air on the switch, I am referring to the nipple that is on the IDM housing.