HVAC experts needed - T-stat questions

[TR Custom Parts]

Decided to pick up a Honeywell CT3500 programmable T-stat while I was at Lowes today. Thought this T-stat was compatible with my system until after installing it and finding a paragraph that says it can't be used with a 6 wire system. They were referring to multistage systems and that it was NOT compatible with those systems.

I have an oil fired forced hot air furnace with central air. There are two zones, upstairs and downstairs. Would having the two zones be messing things up for me? Would having two zones be considered a multistage system??

Figured I would give it a try anyway and everything seemed to be OK until I realized the furnace was running even thought the t-stat was set to cool. All the wires were hooked to the proper terminals as I marked them when removing the wires from the old t-stat which was the traditional T-87 round type.

Since it is over 90 here again, I put the old stat back on and everything is working fine.

 

[quickbrick]

im just a begginer in the hvac field but these guys can help ya.
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[turbosam6]

When you say you have 2 zones, do you mean you have 2 thermostats? You don't have a multistage system, you have a zoned system, its different. If the heat is running at the same time as the A/C, you are powering up the white wire at the t stat. if you have a volt meter, check to see if you have 24 volts (give or take) at the white wire when the problem occurs. Make certain the white wire isn't chaffed or otherwise touching the red, yellow, or green wire.

heres how it works: The red is 24 volts hot all the time. When you turn the fan to "on" or turn the A/C on, the green wire is energized. When you turn the A/C on the green and yellow wire is energized. When you turn the heat on, the white wire is energized. This assumes you have a "call", i.e., the system should be running. Sometimes the thermostat wire is the wrong type and the colors don't correspond. Often there will be a blue wire in place of the yellow. How many conductors do you have? 4? If you like, you can call me at home 217-359-9749, I can walk you through it. HTH

 

[TR Custom Parts]

There's two 3 conductor wires on the original T-stat. Red, white and green wires on each. They were connected to the R, O, W, Y, B and G terminals. Labeled each one as I took them off the old t-stat and transferred them to the proper terminals on the new t-stat.

And yes I have two t-stats in the house. The one in the basement controls just the temp. The one upstairs has all the controls for Heat/AC, fan, auto, etc.

Why would the instructions say it won't work with a 6 wire t-stat I wonder?

 

[turbosam6]

Well, you're almost in need of a tech to come out. They haven't ran the wires in a fashion I could explain. But, "O" is for a heat pump, which you didn't mention. Is the oil heat running, or the heat pump? If its the heat pump, then the "O" terminal is not being energized, and might not be a heat pump stat. Do you have a heat pump?

 

[SloRegal]

If it using the "o" then its a heat pump system, which that ativates the reversing valve.. right?

 

[TR Custom Parts]

It's NOT a heat pump system. Just a simple oil fired forced hot air system. Present t-stat is a Honeywell T87 style with 6 wires connected to it. I also have a T87 style t-stat in the basement that ONLY controls the temp in the basement area, no other controls on it.

Just bought another t-stat and will give that a try.

 

[AsphaltAnihil8r]

NOw why would you take Ol Faithful off the wall(T87f)

Nowbnody even uses the setback feature on the high end stats,,all the ones I come across are in the "HOLD" position,cause they cant figure it out

 

[TR Custom Parts]

I'm at my wits end on this project! Put the newest stat on and turned the breaker on and voila, AC is running. Waiting for the temp to start dropping and nothing is happening. My basement is nice and cool and the damn old stat in the basement is set to 80 but the cool air is coming out of the vents in the basement! No air coming out of the ones upstairs!

I'm not a complete moron and know how to mark wires and transfer them to the proper terminal so what the hell is going on here!!??

Took everything apart and looked for problems with the wires but didn't see anything wrong. Put everything back together with the T87 and everything is fine again.

Thanks for the answers but I think the T87 is going to stay for now. Wasted enough time on this FN stat this weekend.

 

[turbosam6]

Sounds like you have a motorized damper in the system for the upstairs zone, the "O" terminal can sometimes be used to activate that. But most new thermostats activate "O" for the heat pump reversing valve. Dampers are "normally open", so when you turn on the A/C, you energize "O", therefor closing said damper. You might have to stick with the T87, or maybe change to a different main zone control that allows different t stats.

To test my above theory, hook up your newest one again, but leave the "O" terminal disconnected. See if you get air upstairs again.

 

[TR Custom Parts]

Maybe I was reacting too fast. Didn't realize that the dampers took so long to close. Everything is back to normal now. Maybe I will give it another shot when it is cooler out and don't need to have the AC running.

Still can't figure out why the heat would come on when I first powered up the new stat though.

Was pretty much just looking for a small project to do as it is too hot outside to do much right now. Oh well.