Trane Variable Speed Air Handler--Not Varying Speed


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Old 06-12-10, 08:48 AM
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Trane Variable Speed Air Handler--Not Varying Speed

I'm new to this forum and looking for some guidance on a relatively new AC install. I'm trying to figure out which component in a Trane system is at fault for not allowing a variable speed air handler to vary it's speed. Doing some reading here, it sounds like I'm getting shorted on the rated SEER spec, and may be only running 1 of the compressors in the XL20i.

Quick back story: Renovated cape cod house, 2 new compressors, 2 new air handlers, up stairs and down. Trane XL20i's on both, 4TEE3C0A1000AA variable speed air handlers on both. Downstairs has the "comfort link 2" 3 wire thermostat...but upstairs, for whatever reason, has a simpler Trane thermostat with 9 possible wires connected, and 6 actually connected.

Downstairs is hot water baseboard, upstairs is an Aquacoil water to air heat exchanger sitting on top of the air handler. Would this justify the different thermostat?

Did my installer decide to cheap out on the thermostat? Can I replace this myself if they play hard ball?

Second question that confuses matters...without a heating coil installed in these units, is there a way to still run them as heat pumps in the winter, rather than use my boiler? The ComfortLink2 reports the error code for missing equipment when I try to run "heat mode"...

Thanks in advance.
 
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Old 06-12-10, 07:41 PM
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What model # do you have on the 2nd stat? (non comfort link)

Why do you want to run the system as "Heat Pump"?
 
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Old 06-12-10, 11:50 PM
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A good test on the air handler is when the outdoor unit shuts off the indoor blower should shift to a lower speed for maybe a minute before it too shuts off. Be sure stat fan is set to AUTO for reasons stated on other threads.
 
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Old 06-13-10, 07:14 AM
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Thanks for the quick help guys.

2nd Thermostat is a Trane TCONT602AF22MA, listed as a 2 stage thermostat, with installers guide available online.

http://www.butcherdistributors.com/I...installers.pdf

Looking at the setup menus, the thermostat is configured as 2-stage cooling. Doing the "compressor test" in the installer menus seemed to get my outdoor unit to shift between a slower and higher speed. However, these speeds did not seem to change consistently. When I did a test with just 1 compressor, the outside unit was running at full speed (very slow for the XL20i), turning the second compressor on seemed to slow this further, finally going back to the first test was slowest of all. There was variability in this though, since I was running downstairs, and outside.

More confusingly, the air handler never shifted speeds throughout any of these tests. I tried srercrcr's test of checking airspeed when the compressor turns off (thermostat on auto): it remains the same, though the air handler does run for about 1 minute. The air handler does have a smooth start up and shut down, but always to the same speed.

Does this now point to the wiring inside the air handler, versus the thermostat?

Heat pump question was motivated by my 20 year old oil furnace. Isn't a heat pump more efficient until the very cold weather hits?
 
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Old 06-13-10, 09:34 AM
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If your outdoor unit is not a heat pump model, then it's not going to do any good. Unless you do have a heat pump, then yes tht t-stat should be set for it.

Make sure Y1 is wired to Y1 at air handler to Y1 outside, then same for Y2. Otherwise, call the dealer since you are unsure what's going on.
 
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Old 06-15-10, 05:20 AM
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Alright, I think I fixed it...

I confirmed the wiring is correct (best I can tell), and that the compressor is changing speeds appropriately.

I opened up the Air Handler with the encouragement of the installer's guide, and accessed the electronic service panel inside (simple LCD display and buttons). For a 24VAC thermostat, you can set a lot of options on these air handlers from here.

My air handler was set up as a single stage system (wrong--wired for 2 stage). That was easy to change.

Set a slower fan speed for shut down (easy!).
Set my 1st stage fan speed (guessed at 62%)...

More confusingly, the air handler was set for a 3 ton outdoor unit, when I have 2 ton. This changes how much air is moved, along with a CFM/ton menu. 3 tons is not the default, so clearly my installer changed this. Since I have little faith in my installer (not just because of this), I'm trying to decide what the "right" CFM setting is. The blower performance table with the air handler seems to offer a range of CFM options for a 2 Ton unit.

Is this where I break out the HVAC calculation programs?

The 2 ton setting for CFM sure feels like a slow breeze compared to the 3 ton gust that used to blow out...but the air is cooler.
 
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Old 06-15-10, 05:10 PM
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yeah, if the dip switch are not set up right, and the wire not hooked up right, the system is not going to run right.

Glad you got it figured out.
 
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Old 06-15-10, 09:11 PM
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It is scary out there in sophisticated equipment land. Rarely do you find anyone really trained to do setups. And no one trying to make a dollar against the fierce competition is going to have the time or be willing to set down and actually read all that crap from the factory, man if that sucka runs when you hit the switch you run for the van and haul butt outta there. LOL just kidding but it does seem that way sometimes. Atomix congrats on taking charge of your new system you are doing the right thing here,no one cares about your HVAC unit like you do. Enjoy the high seer tranes those babies are sweet.
 
 

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