Goodman 2 stage furnace GMV950905DXA is playing diagnostic games with me

Will B Fixed

Premium Member
Joined
Oct 24, 2019
Messages
4
Location
Ohio
Model Number
GMV950905DXA
Brand
-major brand-
Age
More than 10 years
Hello, Getting pretty frustrated with this furnace as cold weather moves in.. not sure how much info to add today.

Basic problem, does not fire up ALL the time... but has when it feels like it.

It is a Goodman GMV950905DXA

Control board LED flashing code for stuck open low fire negative pressure switch.... but does close with minimal vacuum applied

Programmable thermostat is calling for heat

Checked all the possible normal problems in flow chart and made sure there was vacuum to the safety switches with manometer, also see that the switches do close and conduct 24 volts

Both port nipples clear to inside, and dry, no leaks in hoses

This morning I attached test jumper on the low fire switch (after inducer ran enough) and it fired up ONCE then back to nothing.

Since everything is about 12 years old, I have now replaced front cover negative pressure switch , low fire and high fire negative pressure switches, the Inducer motor and housing, the flame detector, primary limit control, both manual reset rollout limit switches

It does not want to be fixed... am now suspect of the main control board but don't want to throw more money at it if it won't fix it... control board is the ony part besides the gas valve that has not been replaced.

Intake clear, exhaust clear, filter cleaned, condensation draining out...

How often do main control boards go bad? seems a long shot but running out of options

Have I missed anything? Happy to add more when asked

Am I in the Twilight zone ?
 
Last edited:

Will B Fixed

Premium Member
Joined
Oct 24, 2019
Messages
4
Location
Ohio
UPDATE... had to move forward (sidways) replaced the main control board now... still no fire and getting the same three blink fault code for stuck open low fire pressure switch... VOM set to ohms on pressure switch shows it is open, and DOES close when the induction motor pulls a vacuum on it. All the pressure switches test good like this. 27 volts everywhere it should be..

I guess there are not many members who frequent the HVAC forum here.... does anyone that might see this know of a better place to ask for help without being a professional HVAC tech?
 

Jake

Appliance Tech - Admin
Staff member
Joined
Aug 24, 2004
Messages
102,680
Location
McMullen Valley, Arizona
Hi Will,

Bob who used to help us here in the HVAC forum passed away a couple years ago, was waiting to see if anyone else wanted to fill in for him. I may have to close this HVAC forum if no one wants to help here.

Other than that, you can try RepairClinic here:

Jake
 

Will B Fixed

Premium Member
Joined
Oct 24, 2019
Messages
4
Location
Ohio
Thanks for the reply Jake...

Thanks for the suggestion, but it's no good using a trouble shooting list as this problem defies the normal flow charts for some reason.. I will certainly have a look anyway..

Do you think moving HVAC questions into the mainstream appliance forum might do any good? Seems like most who need or offer help with other appliances would not even look in here now.. but just might find interest if in the general list etc.

Best,
 

Jake

Appliance Tech - Admin
Staff member
Joined
Aug 24, 2004
Messages
102,680
Location
McMullen Valley, Arizona
Do you think moving HVAC questions into the mainstream appliance forum might do any good?
Nope, not without a dedicated HVAC tech that can help us here.:)

Jake
 

Will B Fixed

Premium Member
Joined
Oct 24, 2019
Messages
4
Location
Ohio
UPDATE;

Heat is back on... LED code on main board does not know everything,

Intermittent conductivity of connector/wire between secondary rollout switch and the low fire negative pressure switch voltage input side.
Solid feel to connector, tested good when tested.... opened when it felt like it.

But still happy to have new components in place for the next decade of use. with good prices and service from RepairClinic it was reasonable to do
 
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