2-stage furnace, 2-stage t-stat wired like a 1-stage system?

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Old 02-24-13, 07:27 PM
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2-stage furnace, 2-stage t-stat wired like a 1-stage system?

I have a 2-stage furnace (Trane TUD100R9V5K0) and a 2-stage thermostat (Trane XT302C). I recently replaced a defective control board in my Trane furnace. While doing that, I discovered that the white wire from the t-stat was connected to both the W1 and W2 terminals on the furnace control board. I connected the new control board the same way for now, but I don't think this is the correct wiring to take advantage of a 2-stage system.

I checked at the t-stat and found that the White wire is connected only to the W1 terminal. Nothing is connected to the W2 terminal of the t-stat.

The black wire which I believe would normally be connected to the W2 terminals at both the t-stat and furnace is present, but unconnected at both ends.

Is there any reason why someone would wire it that way? It was like this when I bought the house. I want to wire this thing correctly, but before I do I wanted to find out if there is any reason to leave it as-is.

Thanks.
 
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Old 02-24-13, 07:42 PM
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I would absolutely install the wire for W2. Here is a copy of the install manual. You need to make sure it is setup for a 2 stage heating system.
 
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Old 02-25-13, 07:08 AM
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If so not sure why they did that.. Maybe the last owner didn't like the ideal of the long steady run time on 1st stage and was worried they were wasting gas!

Go ahead and wire up for two stage, and you'll get the best comfort this way.

Like Kevin said, set the stat up for this. It starts on page 4 on how to get into the isntaller set up menu.

In Set-up #3 set it to 2.
#4 to 2
#5 to 3
and #9 to 2.

Is your A/C a singel stage unit? Also, we would be happy to go over the dip switch settings to make sure you have them all set up right, also other profiles to take advantage of such as Comfort-R.
 
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Old 02-25-13, 11:14 PM
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Thanks for the replies.

This evening I wired up W1 and W2 correctly for two stage operation. I notice the difference in operation immediately: if the temp dips 1 deg below the stat setting, heat comes on with first stage only. If I move the stat setting up even 2 deg above the temp, it comes on right away with 2nd stage heat.

I believe I've also figured out a couple things:

First, the old control board (CNT03078) must have had a fixed W2 delay setting. It used to run on low heat most of the time, and only occasionally kicked into 2nd stage heat, probably only after running longer than the delay time. The new board (CNT06015) has an adjustable W2 delay which is currently set to the factory setting, "off". When I wired the new board the same as the old one, this caused 2nd stage heat to come on immediately. With W2 wired correctly, and the W2 delay still set to "off", the stat should now directly control when stage two heat comes on. Let me know if I'm right or wrong about any of this.

Second, If I'm right about the above, then the previous owner or HVAC installer probably thought the fixed W2 delay on the old control board was good enough to run a complete heating cycle on 1st stage heat in most cases on a typical winter day here in Texas.

Here are the settings I currently have:

At the stat, the installer setup options are all the factory setting. Jay, the settings you recommend would lower the number of cph's. Does this force the unit to run longer cycles using 1st stage only, or is it better in some other way?

The DIP switches at the control board (CNT06015) are set like this:

S3 (1-4): off off off off
S4 (1-4): on on off on
S7 (1-4): off off off off

The above are all factory settings, except for cooling delay which is set to Comfort-R.

My outdoor AC unit is single stage, I believe: Trane XE1000, Model number TTR060C100A3. I've not yet tried running the AC with the new control board.

Sorry for the long post, but thanks again for the replies and the help.
 
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Old 02-25-13, 11:40 PM
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I can't help with the thermostat settings but yes, that IS the way the furnace is supposed to work. You CAN change the "offset" or "differential" from the second stage cutting in through the thermostat's setup menu, Jay will explain how. I have mine set to bring in the second stage if the temperature drops more than three degrees from the primary setpoint. The ONLY time my second stage burns is when I manually change the setpoint up more than three degrees, otherwise it cycles on first stage only, even in the coldest weather.
 
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Old 02-26-13, 07:56 AM
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The lower CPH will let the furnace run a little bit longer for better comfort than short cycles.

Not sure if your board came with a new sheet for the settings vs what is said on the specs and diagram on the blower door, but set them up as posted.

Dip switch settings, the heating speed will be hard to say for sure but I'd suggest doing a temp rise and set the blower up to have teh temp rise in mid range.

Set the cooling blower speed to 400 cfm per ton, your unit is 5 ton.

Do you have any jumpers between other stuff on the t-stat hook up?
 
 

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