SOLVED! OFF TOPIC - Any HVAC Furnace experts here?? I need help!!

[Reinen]

I've had this happen and the root cause wasn't mentioned yet.
The fan has a capacitor to help start it up. It's in the fan compartment. If it looks at all swollen, it's bad and that's your problem. If it's not swollen it still might be the problem but it requires testing equipment to confirm (or the proverbial throw parts at it). The furnace will shut down if the fan doesn't spin up adequately and it needs the capacitor to do that.

This part right here gave me deja vous about my bad capacitor not spinning up the fan adequately.

the fan relay will click on and off several times and eventually the fan will start after about 10-15 clicks with the fan turning on for longer periods of time each time but usually not for more than a fraction of a second to 1 second.

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[jaymz]

I have not checked it. I’m not even sure how to, I imagine I can get on the roof and look? But then what?

You could TEMPORARILY disconnect the exhaust duct at the unit and see if you get normal operation. If you do, there’s likely an obstruction in the pipe, if not, it’s probably clear. Does everything work normal when you call for A/C?

 

[Beachcomber72]

I was certain that based on our past issue and your matching videos that the thermostat was going to be your culprit. I wish I was there to be onscene with you.

 

[Beachcomber72]

I got it!!!

Remove the furnace and bring it with you out to a trail we’ll all meet at and we will definitely get it solved there. I’ve never seen jeepers on a trail not solve a problem.

 

[Beachcomber72]

By chance is there any oxidation or debri on the flame sensor itself or corrosion on the electrical connector going to the flame sensor? Just to rule it out clean both parts really well by scraping a clean bare surface on each.

 

[Caliguy]

Ok, so at this point it literally has to be one of two things

either new pcb control board

or

clog in the exhaust.

So far we have

new thermostat
New flame sensor
New gas valve
New capacitor
New air filter


when jumping R and W - inducer turns on and works as intended

when jumping R and G fan turns on and works as intended

when turning in heat mode on thermostat, furnace works as intended for about a minute then surges on fan without turning anything else on

working theories:

1. exhaust is clogged and pcb is telling furnace not to turn on coils/gas

- this begs the question, why does it work for the first cycle when turning on heat mode for a minute

2. Bad pcb not triggering the right components

- this begs the question, why does fan and inducer work when jumping the wires

 

[Caliguy]

By chance is there any oxidation or debri on the flame sensor itself or corrosion on the electrical connector going to the flame sensor?

iv replaced it, I have also sanded from 1000, 1500, and 2000 grit and polished it

 

[Beachcomber72]

iv replaced it, I have also sanded from 1000, 1500, and 2000 grit and polished it

And the connector going to it?

 

[Caliguy]

And the connector going to it?

nothing about it seems off, just looks like a normal wire

 

[Beachcomber72]

https://householdair.com/furnace-gas-valve-not-opening/

 

[Beachcomber72]

nothing about it seems off, just looks like a normal wire

Double check the leads going to the gas valve too.

 

[Beachcomber72]

How many wires are coming out of wall to the thermostat and what colors are they and what model of thermostat are you using?

 

[Caliguy]

https://householdair.com/furnace-gas-valve-not-opening/

This doesn’t seem applicable, it has an electric coil that glows, the gas is then released and ignites.
The problem is when the fan surges, nothing else turns on, not the IGNITER, nor inducer or has valve.

however, when turning in heat mode for that first cycle, it all works flawlessly for a minute.. inducer kicks on, igniter glows orange, gas valve turns on and we got blue flames, then tan comes on.

bad part is after, fan turns off, then fan relay and fan surge on and off over and over again. Sometimes 11 times on and off then tan is on for about 30 seconds, then 13 times then in for 30 seconds, then 14 time

Double check the leads going to the gas valve too.

tech installed it. There are two leads to it, a yellow and green, and a blue. I don’t know if it’s correct or how to check if they’re plugged in the correct slot. To be honest, I’ve tried switching them and there was no difference

 

[Caliguy]

How many wires are coming out of wall to the thermostat and what colors are they and what model of thermostat are you using?

I just got the Sensei touch from Home Depot. The wall has a red, white, yellow, green, blue

red wire to RC on thermostat
White to W
Yellow to Y
Green to G
Blue to C

it’s the same on the pcb

shouldn’t be an issue as nothing was changed here when it stopped working correctly

 

[Beachcomber72]

Check this out.

https://webapps.emerson.com/resources/wire-picker.aspx

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