Furnace Questions

[wrench409]

My Furnace - Frigidaire FG6RA - installed in 2008 has begun to cycle out after a complete startup. It's an 80% type.

First, it has LEDs to flash fault codes - RED on for Power and is used to flash codes when codes are present - YELLOW on for the flame sensor and it flashes when it is out of range. However, no codes are displayed.

1. Set tstat to temp above ambient - call for heat.
2. Inducer motor spins up.
3. Igniter glows normally.
4. Gas valve cycles on.
5. Burners ignite.
6. Yellow LED comes on signalling the flame sensor is providing signal.
7. After burning for a very short time - 45 seconds, the fan blower motor powers up.
8. After 60 seconds the Yellow LED goes out, the system shuts off and this cycle repeats.

Things I've checked or done so far:

a. New filter - get's one every 4~6 weeks anyway
b. Removed the flame sensor - not very much build up, but I cleaned it anyway. This is the most common on these NG furnaces and it was worth a shot.
c. Checked the pressure switch port to the plenum for buildup, found none.
d. Checked for wiring connection issues in the unit - found none.
e. Cussed a lot.

I am experienced in troubleshooting flash codes to check sensors and circuitry since the 80's. I am trained in electrical and electronics. I already do my own home A/C service (same unit).

This damn thing has me pulling my hair out. All the vids on the net say clean the flame sensor and you're done. It's indicative the flame sensor has failed but not knowing the sensor specs, I'm not sure.

No codes to troubleshoot. No sensor data to check input/output on my meter. HVAC techs want $28 on the net to answer and local HVAC guys won't answer anything.

I hate throwing parts at anything until it's fixed. And the local supply house wants $58 plus S&H for a $10 sensor.

Any other stuff I need to look at?

I'm stumped.

 

[zmaxmotorsports]

Have you tried jumping the white and red on the board to call for constant to see what it does?
If it continues to do it even with stat bypassed Id go back to the flame sensor and make sure it hasn't separated internally from its base.

 

[JackDiddly]

I would also jump out R and W at the unit, eliminate the t-stat. If that doesn't work I would get a magnehelic gauge or manometer on the inducer port and verify that it is producing what is needed to make the pressure switch. If there is build up in the chimney or vent pipe or bad inducer motor/capacitor you could be having a prob that way.

 

[welder4956]

Did you try to take a piece of straight wire (I use 1/16" tig wire) and clean out the port on the collector pan that the hose to the pressure switch connects to? I have to clean mine just about every year. Just pull the hose off and push the wire through.

 

[wrench409]

Yes, I cleaned the port (already mentioned that in my troubleshooting).

I removed the old thermostat and jumpered the RED and WHITE wires at the wall so the board calls for heat. It now keeps running in heat and we are warm. I'll get toasty and take that wire off shortly.

I guess the tsat is bad. Old round dial Honeywell wall unit. I'll head out tomorrow for a battery powered digital unit. She wife will have to adapt (she hates anything with LED'S or LCD screens) or shiver. LOL.

No fault codes is a good thing. Simple fixes are way better than hearing a service guy say 'That'll be $360 please'.

Thanks everybody!

 

[Radamsiii]

In that Honeywell thermostat on the bottom right is a dial with numbers this is the heat anticipator. Try moving it to longer cycles.

 

[wrench409]

Thanks!

The sad thing is I bought the newer version of the Honeywell thermostat. I do NOT like it's operation at all. The reviews were mixed on the big box websites but I had to do something.

Anyway, I did finally find a Youtube that mentions the anticipator settings.

https://www.youtube.com/watch?feature=player_embedded&v=WYqK-aQqWfw#t=10

When I looked the old one over, that setting was slid way far to the right (not the .5 he mentions) causing the short on/off times he describes. I will reinstall it in the next few weeks to check it's operation. I did not want to upgrade to the battery operated models that are digital as the wife dislikes anything electronic (she still listens to LP's!).

Wish I'd found it sooner!

 

[dfiler2]

Just one comment, get a thermostat that uses the "C" terminal for power, two years in a row I got a call from home saying the heat wasn't working, battery in the thermostat both times. I put in a Wifi thermostat this year and I love it.

 

[theoldwizard1]

My Furnace - Frigidaire FG6RA - installed in 2008 has begun to cycle out after a complete startup.

I'm not sure I know what your mean by "cycle out". Turn it self off before the thermostat is satisfied (build still below set temp) ?

Mine does that on EXTREMELY cold (< 0F) and windy days. The heat exchanger over temp is shutting off the furnace. This because the down stream main duct must make 2 sharp 90° turns before it enters the main trunk line. Heat backs up and trips the over temp.

I can't reduce the gas pressure anymore and it would a royal pain in the *** to try and retro fit a bigger blower. Luckily, this only happens once every couple of years. House still will maintain about 60F.

 

[zmaxmotorsports]

I'm not sure I know what your mean by "cycle out". Turn it self off before the thermostat is satisfied (build still below set temp) ?

Mine does that on EXTREMELY cold (< 0F) and windy days. The heat exchanger over temp is shutting off the furnace. This because the down stream main duct must make 2 sharp 90° turns before it enters the main trunk line. Heat backs up and trips the over temp.

I can't reduce the gas pressure anymore and it would a royal pain in the *** to try and retro fit a bigger blower. Luckily, this only happens once every couple of years. House still will maintain about 60F.

Have you checked the A-coil to see if its clogged?Some of those 3m filters are pretty restrictive also.

 

[[email protected]]

It is probably your flame sensor, remove it and clean it with sand paper. Hopefully it works.

 

[wrench409]

It is probably your flame sensor, remove it and clean it with sand paper. Hopefully it works.

Been there, did that.

 

[bazar01]

Have you checked the A-coil to see if its clogged?Some of those 3m filters are pretty restrictive also.

+1. (for theoldwizzard1 post)
I would check the temp rise across the heat exchanger.
It may be tripping on high temp.
If A-coil is clean, I would throttle the gas valve to reduce flow if gas pressure is correct.
This will reduce flame strength so you don't have to go to a bigger fan.