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airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8378
Experience:  Furnace, A/C and heat pump specialist.
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Problem … 14 years old - Goodman GMPN Multi-Positional Gas

Customer Question

Problem … 14 years old - Goodman GMPN Multi-Positional Gas Furnace Dependable 92 (GMPN100-4) Starting furnace sequence - Red LED indicator is STEADY - Inducer running great - Igniter glowing hot (20 seconds) But NO gas FLAME !!! - 3 more repeat NO gas FLAME … during cycling’s the LED indicator is STEADY … Furnace locks out, then Red LED indicator blinking slowly constantly every second forever … Primary heat exchanger is in great shape and no rust or cracks and cleaned with low pressure air & vacuum. Secondary heat exchanger cleaned (tubes cleaned also) Pri***** *****mit switch OHM reading 0.1 – Pressure switch 3.2 OHM with manual vacuum – Rollout switches are closed – Gas valve solenoid readings .599 OHM. Any idea what could be the problem?
Submitted: 1 year ago.
Category: HVAC
Expert:  BillyHvac replied 1 year ago.

hello,

At any time do you get 24v on the wire to gas valve from roll out switch?

Customer: replied 1 year ago.
download furnace - First rollout is connected to Gas Valve. do I have to chech without gas on or off?
Customer: replied 1 year ago.
Just wondering R U there ?
Customer: replied 1 year ago.
Are you around still?
Expert:  BillyHvac replied 1 year ago.

sorry had to clean sat dish off (snow)

You will put one meter lead to blue wire on valve and other to ground.

See if valve gets 3 seconds of 24v after ignitor glows aprox 20 seconds

Customer: replied 1 year ago.
Sorry 4 U im north of Toronto and hardly any snow here !!! - You wrote ... You will put one meter lead to blue wire on valve and other to ground. Q GAS off or On also disconnect wires or not?See if valve gets 3 seconds of 24v after ignitor glows aprox 20 seconds
Expert:  BillyHvac replied 1 year ago.

power on, gas valve on

Expert:  BillyHvac replied 1 year ago.

leave wires attached

Customer: replied 1 year ago.
Volt meter 0.11 V
Customer: replied 1 year ago.
I got 0.1 Volts
Customer: replied 1 year ago.
0.11 not 0.1
Expert:  BillyHvac replied 1 year ago.

thank you....this means you have a bad circuit board. It sends al signals except the final 24v to the valve. This is a circuit board defect.

No fix except to replace the circuit board

Billy

Customer: replied 1 year ago.
Can i check voltage to the gas valve? Im suspecting valve / solenoid ? Solenoid has 0.599 Ohm only - i belive it has to by arroung 1500 ?
Expert:  BillyHvac replied 1 year ago.

that is what we were checking at the valve after the ignitor glow.

You have 2 choices:

24v goes to valve for 3 seconds during ignitor glow but no gas = bad gas valve.

NO 24v to gas valve during ignitor glow = bad board.

It is either board or valve.

The 24v test tells us which.

Customer: replied 1 year ago.
What if i connect meter to Blue & roll out switch wire (purple) instead Blue & ground, then run the test again?
Expert:  BillyHvac replied 1 year ago.

you should be testing the wire that goes to valve from roll out...not the wire that goes back to board

Customer: replied 1 year ago.
Sorry i don't understand "back to board" ??
Expert:  BillyHvac replied 1 year ago.

gas valve has 2 wires..one comes from roll out....the other wire runs back to circuit board...the wire back to board is common and will not read voltage

Customer: replied 1 year ago.
You mentioned one meter prong to ground other is to blue wire they all connected to the board aren't they?
Customer: replied 1 year ago.
This is a single not two stage furnace
Customer: replied 1 year ago.
only two wires to GAS VALVE
Expert:  BillyHvac replied 1 year ago.

I know....that is why I said test the wire from roll out to gas valve....the other wire (thats 2 all together) goes back to board. The GMPN is a basic single stage gas valve.

You should be able to tell if valve gets 24v no different that how a light bulb gets 120v

Customer: replied 1 year ago.
then why i have to meter The Blue wire to Ground - Why not Blue & Roolout wire to test for 24v
Expert:  BillyHvac replied 1 year ago.

my schematic shows blue as the 24 in from rollout.

But that is also why I say wire from roll out.

You can also remove both wires and hook one wire to one meter lead and the other wire to remaining meter lead.

Expert:  BillyHvac replied 1 year ago.

but they have to be off the valve this way

Customer: replied 1 year ago.
Billy - Yes its crazy schematics -- All my roll out switches have people wires! ill try it in 10 min now we getting somewhere .. Looking forward for 24 volt readings get back to you in 10 min
Expert:  BillyHvac replied 1 year ago.

this will boil down to the 24v present or not...24v present = bad valve

no 24v = bad board

Customer: replied 1 year ago.
Billy i got 0.27 - 0.37 for 2/3 seconds - the numbers i think are great BUT - i just don't understand why . did i set my meter wrong?
Expert:  BillyHvac replied 1 year ago.

what setting is on your meter or can you post pic?

Customer: replied 1 year ago.
No picks but im sending a drawing to see
Expert:  BillyHvac replied 1 year ago.

set for 200 and test a working outlet. verify 120v....then leave set for 200 and test valve

Customer: replied 1 year ago.
I have 120 V coming in to furnace
Expert:  BillyHvac replied 1 year ago.

yes...I was testing meter...if it reads 120v for a supply voltage...then it should read a full 24-28v for gas valve.

Customer: replied 1 year ago.
Should i disconnect the Thermostat and JUMP >>> Red &White to call for heat?
Expert:  BillyHvac replied 1 year ago.

if you are testing while ignitor glows...then r to w is not needed. R to W is is the furnace doesnt start at all...you have exhaust fan, glow etc...so thermostat works.

If you test the gas valve the entire time the ignitor glows until it goes out...And...

no 24v reading happens = board

24v happens is bad valve

Customer: replied 1 year ago.
One more thing .... Let’s say one of the rollout switches out of four are defective? Can it be a defective circuit to run the 24 V test? Reason being for my question is that prior my furnace problem I had to reset one of my rollout switch time to time to run heat. (I never had Flame Rollout) after several days of manually rollout switch resetting my furnace gave up. Then I cleaned Primary & Secondary exchangers 100%. So my question again … What is if one of the rollout switches are defective? Can it be a defective circuit to run the 24 V test to gas valve? Also gas valve solenoid reading is only 599 ohm
Expert:  BillyHvac replied 1 year ago.

you are getting a flame fail code..not a roll out or limit code.

BUT....all you would do is work backward following that wire....looking for 24v.

No different than looking for power to an outlet. If not at one point back track to next...or start where you know you have 24v...like the first roll out or limit. The schematic on the blower door shows the path

Expert:  BillyHvac replied 1 year ago.

we care about voltage more than ohming coils at this point. find yur 24v...and go from there...

Customer: replied 1 year ago.
Billy - thank you for your time trying to help me tonight – doing some additional tests tomorrow. It’s getting late. Can I get back to you tomorrow? Thanks much! Steve :)
Expert:  BillyHvac replied 1 year ago.

Ready to try some more?

Customer: replied 1 year ago.
Hi Billy - im back - had now time to go ahead with my furnace problem. Just for now i have another creation i have before im retiring for the night. Question is after 3 times running furnace with no Gas Flame (i can hear Gas valve or solenoid CLICKING ) Also LED solid ... But after 3 repeat i have Slow blinking LED light for ever on till i shot off the system.
Expert:  airheatman replied 1 year ago.

Looks like Billy has opened question up for other experts.First of all take a look at this diagram and tell me if wires and colors match what you have .

Customer: replied 1 year ago.
Hi Airheatman - This is Steve - The wires and colors do match. Few weeks ago after cleaning first an secondary heat exchangers i had fast led blinking. Then i checked out the diagram and switched one wire according to the diagram. I have Solid Red LED light at start. I have 27 V at gas valve. Running 3 times - No Flame !!! - Then LED blinking (approx every second) for ever until i shoot it off.
Customer: replied 1 year ago.
Hi Airheatman - This is Steve - The wires and colors do match. Few weeks ago after cleaning first an secondary heat exchangers i had fast led blinking. Then i checked out the diagram and switched one wire according to the diagram. I have Solid Red LED light at start. I have 27 V at gas valve. Running 3 times - No Flame !!! - Then LED blinking (approx every second) for ever until i shoot it off.
NOW What if? … Can I bypass (ONLY temporarily) one rollout switch by disconnecting wires then connect them together to check if rollout switch malfunctioning? I’m suspecting upper middle because all my problems started with that. I had to reset it many – many times manually for few days to have heat. Then furnace stopped working. At that point I CLEANED & checked out Heat exchangers. The look great! No rust or cracks. Also I never experienced any gas/flame rollout before. So what if the rollout switch defective? Can I test the furnace by bypass the rollout switch? I assume if rollout is defective then Gas Valve will not open even if I got 27V.
..
Expert:  airheatman replied 1 year ago.

Good evening Steve. If you are getting 27v at gas valve, either the gas valve is defective or you have a gas pressure issue.To determine which, attach a manometer or gas pressure gauge that reads inches of water column to inlet and out sides of valve.

If you had an open limit the led would blink 4 times pause , 4 times pause until limit is closed.

If limit was open we would not get igniter.If rollout switches were open we would not get the 27v to valve.

Customer: replied 1 year ago.
Hi - I have gas oven and no problem. I don't have manometer. I have solid LED. Igniter is glowing/working.
Expert:  airheatman replied 1 year ago.

OK with ignitor glowing do we get the 24 to 28 v to gas valve?

Customer: replied 1 year ago.
27 V
Customer: replied 1 year ago.
27 v and i can hear Valve clicking
Customer: replied 1 year ago.
Forgot to tell you i bypassed Termostat by connectin R & V wires
Expert:  airheatman replied 1 year ago.

OK if all other gas appliances are working, most likely a bad gas valve.If we are getting 27v to valve there are no limits,pressure switch or rollouts that are not doing what they should.If any of these were an issue, the board would not send 27v to valve. The solenoid sounds like it is clicking but gas valve not opening.Replace valve and this should solve your problem

Expert:  airheatman replied 1 year ago.

At this point of furnace sequence valve should be open.To question any other component such as a limit or a pressure switch would be like a car engine not starting and wondering if low tire could be the issue.

Customer: replied 1 year ago.
Ok ill order gad valve next couple of days - Can i get back to you after its replaced?
Expert:  airheatman replied 1 year ago.

Absolutely.You can wait until we are finished to rate answer.

Customer: replied 1 year ago.
Thank and have a nice evening!
Expert:  airheatman replied 1 year ago.

forward to hearing back.You have a great evening too.