FIXED Goodman Furnace Gremlins - stopped heating

[Kraynek]

Model Number

GKS90703BXAD

Brand

Amana

Age

6-10 years

I'm on a bit of a wild goose chase here lately to fix my furnace. Put a new filter in and started it up for the season. It had been running the last few weeks just fine. Earlier this week, it stopped heating and would suck and expel air through the intake/exhaust, but wasn't lighting or running. I cleaned the ignitor and flame sensor, and when I turned the power back on the furnace lit, went through a cycle, and then went back to the suck/expel behavior with no heat. At that point I noticed the error code of 2 flashes - pressure switch stuck closed - so on the advice of my local parts house I replaced the vacuum pressure switch. Turned the power back on - same behavior where it would run one cycle, turn off and give the same 2-flash error code. Next suggestion from the parts house was to replace the induced draft blower. I picked that up yesterday and went to put it in this morning. Prior to installing it, I turned on the power to see if I could at least get the place warm for the morning. At that point, the furnace didn't come on at all and immediately showed an error code of 3 flashes - pressure switch stuck open. I installed the new blower and the result is still the same - furnace won't heat at all and 3-flash error code. I tried reinstalling the old vacuum switch just in case the new one was bad and got the same result. If I suck on the vacuum line I can hear an audible click.

Any guesses where to go next?

 

[viper75x]

I'm no expert, but I have been having problems with my furnace lately as well. It looks like you model could have two pressure switches, and since you have an issue with that one particular switch...
First, I'd check for any physical blockages to the air flow. I just noticed last night that the insulation is coming of a side wall and inhibiting the air flow. Check the exhaust flue as well, meaning visually inspect. Then I'd check the wiring connections, terminals, wires, etc. Put your meter on both switches and test continuity across each lead. I am not sure what you're supposed to get, but if you can check it while in operation you might be able to see if it is working or not.

Third, there are other limit switches you may want to check as well - one of my pressure switches is in-line with three other switches (thermal cut-off, two I think, and I forgot what the other is).

You may also want to check the output voltages to the blower motor, induction/vent motor and check amps if you can. Any of these could have some effect that may contribute to the problem.

When you say it 'went through a cycle', do you mean that it ignites the gas and burns for X minutes? (When I get home tonight I am going to take a video of my furnace cycling - after I fix the insulation, so I can get accurate time measurements of each event during the cycle. Mine wouldn't light so I replaced the ignitor then the control board. Now - it cycles as expected then shuts off.)

Well, that's all I got! Hope it helps! Attached is a manual I found for your furnace if you didn't find it already.

 

[Kraynek]

Thanks, Viper. That helps out a lot. The manual is especially helpful given that this furnace came with the house, but the previous owners seem to have lost it.

For your question about cycling:
Yes, it would ignite, burn gas, and run until the temperature in the house was over the temp on the thermostat. Then it would shut off and show the two flash code. Starting yesterday, though, the furnace doesn't cycle and goes straight to the three-flash code with no delay.

I took your advice on tracing wires and checking. Here's what I got:
Vacuum pressure switch - has continuity back to main board on both wires. When I turn the furnace on it measures 24 volts across the two wires. It looks like this is correct.
Induced draft blower - has continuity back to main board on both black and white wires. When I turn the furnace on I see no voltage, and it looks like it should be at 115V.

Does this smell like a main board replacement is in order?

 

[viper75x]

Are you able to test the pressure switch's operation with the meter? I'm not sure if you'll see much on a DMM, unless it's a good one, but with an analog meter you can definitely see the needle move. I'm not sure how long the pressure switch(es) stay closed/open during the heating/cooling cycle, though. Haven't gotten that far yet.

And you checked for intake/exhaust blockages, correct?

Also, I'm assuming you have bypassed the door switch while performing these tests and the switch stays closed the entire time, not accidentally opening causing a problem.

Yeah, that motor is 115v, according to the diagram. Assuming the new motor is good it might be the board. Unless there is something telling the system not to run the motor, although on my furnace that is the first thing that starts up in the normal cycle.

 

[Kraynek]

Yes to the analog meter, but I didn't see much other than it getting ~24 volts when I turned power on to the furnace. The furnace still doesn't light and run, so it's hard to tell what it might do next.

For blockages - I checked the intake (felt under for a draft from outside air, tried to run the furnace with the front top cover off, switch still pressed). The only check I did on the exhaust was looking in the pipe when I replaced the induced draft blower. I'll see if I can take a closer look tonight.

Yes to the door switch being pressed down during any of the tests when i had that door open.

The new board was supposed to arrive today via overnight FedEx. New delivery date is Monday - I hope FedEx is sandbagging since it's supposed to get cold here in Denver on Sunday.

 

[viper75x]

Good luck with the board and FedEx delivering on time! Hope it works out without replacing more parts.

 

[viper75x]

If you're still battling the gremlins, check out this vid:

 

[Jake]

Video is unavailable it says to me.

Jake

 

[viper75x]

Yeah, it's Youtube - Word Of Advice TV - How a Furnace works.

 

[Jake]

You mean this one:

Jake

 

[viper75x]

Yeah, how did you get that to work?

Also, have you read through my post from Friday?

 

[Jake]

Yeah, how did you get that to work?

All you have to do is copy the Youtube link code to share it and paste it in the post.

Also, have you read through my post from Friday?

Yes, but I don't know anything about working on Furnaces, sorry.

Jake

 

[Kraynek]

Thank you for all the help. FedEx finally came through with the delivery today - next day air ended up being a little more like standard ground. I swapped out the wires from the old board to the new board one by one, turned out the power, and for the first time in about a week we have heat. It's gone through several heating cycles without an error code, so I'm cautiously optimistic that we're in the clear.

Only real issue I had was that there were a few more terminals on the new board than there were on the old one. So the top right corner of the board got a little dicey. I believe I reasoned through it correctly (top to bottom, skipped the terminal that wouldn't fit a connector, etc.), and I feel like the furnace's functionality is a good sign. I'll take a look through the wiring diagram tomorrow just to verify.

 

[Jake]

Excellent, glad to hear the new main control board fixed it.

Here's the main control board for your model, in case others need it too:
Furnace Control Board PCBBF112S


Jake

 

[Kraynek]

Jake - thank you for marking this fixed. A few closing thoughts for the group:
1) Lots of great help from the people on the message board. viper75x helped out a ton.
2) I initially replaced the vacuum pressure switch. In hindsight, I probably would have done that as part of the process again. If I understand its function correctly, if you gently suck on the tube and it doesn't click, it's definitely broken; if it does click, it's still possible it could be broken. (Please correct this if I'm not understanding failure modes here.) Only difference is I would have ordered it from a place like RepairClinic because the price was easily 2x at the local parts supply house.
3) Where I went wrong is I bought and replaced the induced draft motor without thoroughly checking if the existing one was getting voltage. I believe the main control board was going through its death throes at the time (initially 2 error flashes, later 3), so it's possible I may have gotten a false positive even if I had tested it. Still it would have been a good thing to check.

I'm happy with the outcome, I learned a few new things about how furnaces work, and I ended up with a few spare parts. Thank you all for the help and I look forward to working with you again. Just not too soon, of course!

 

[Jake]

Sounds good @Kraynek thanks for the added information.

Jake