Two stage furnace wiring

[GMJim]

Hello all. I moved into my new to me home last March 2018 and during conversations with the previous owner it was mentioned that the 7 year old forced air gas furnace was a two stage. As time went by as with a new home I was busy fixing up things and wasn't concerned about the furnace, in other words it kept us warm! Last Christmas my son in law gave us a ecobee4 electronic thermostat and I just got around to hooking it up. During the wiring of the new stat I got to a point where the thermostat showed (Furnace Stage 1)? I started to investigate why I couldn't set it up as a two stage and called ecobee and found that I needed a wire from the W2 terminal on the board to the W2 terminal on the stat which I don't have.

Now as an auto mechanic I'm no stranger to circuit boards and wiring but not familiar with furnace wiring. My furnace is a York TM9V100C16MP11A and when looking it up some of the literature indicates it is a two stage. My dilemma is that the original thermostat (York TH8321U1055) didn't have the W2 terminal hooked up either. Could someone please enlighten me about this? Should this terminal have been hooked up all along and should I bother to hook up the W2 to the new ecobee4 stat. It would mean fishing a new wire but I think it could be done fairly easily.
Thanks
Jim

 

[brewchief]

I don't see many yorks around here but every two stage furnace I do see has the ability to run off of a single stage thermostat, there is normally a jumper or dip switch on the circuit board to switch between a single stage or two stage stat. When running off of a single stage thermostat there is a timer that will bring the second stage on after so many minutes, often 10 or 15 minutes(this may be adjustable depending on furnace).

Running a new wire so the thermostat can call for second stage is nice and can increase comfort in some cases.

Sent from my SM-G965U using Tapatalk

 

[GMJim]

Thanks brewchief but I don't know how a two stage furnace should operate. What advantage it has over a single stage and if I should hook it up. My thermostat is capable of operating a two stage furnace.
Thanks

 

[brewchief]

You will get longer run times running off the stat for 2 stages, many times it will never go up to high fire, if you make a large change in temperature at the thermostat it can go right to high fire to bring the temp up faster.

Longer run times at low fire will normally mean more consistent temperatures and better comfort.

Controlling the staging with the thermostat is better in theory but in practice you might not notice much difference.

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[GMJim]

Thanks for the explanation. It may be my imagination but my furnace seems to have higher blower speeds from time to time? Since I don't have the W2 wire hooked up is that possible? This is why I think I'm confused about this 2 stage thing.