[ellud]

Hi all,

New member here. Great site. Lots of info.

Here's my problem. Just had 2 units added to my house which already had 2 Trane XV80 furnaces installed. Builder only offered 10 SEER units so I opted out and contracted it out myself this spring. The upstairs unit I just put a regular XR14 AC unit. The first floor and basement unit, I went with a XL16i HP. I can go into my thinking on this if anyones curious but that's not my dilema now. The contractor I used seems pretty knowledgable and is Trane certified. It's just that I live in the Chicago area and I don't think many HP's get installed here.

I think the Comfort-R is working good on the upstairs unit. It's a 2.5 ton. The control panel has the W14 jumper cut and I added the jumper from Y to O per a post on this site and reading the installers guide. Airflow goes from 500-700-800 CFM like I thin it should, so all jumpers appear correct.

The unit with the HP is the one I'm concerned about. It's a 3 ton 2-stage and it seems like it's always bypassing the first stage no matter what the outside temp. The thing I can't figure out is the wiring from the stat.

1. He has the first stage cooling going to the Y connector and the second stage from the stat going to the BK/TWIN whatever that is.

2. The O from the stat goes directly to the HP O. Does it need to connect to the contrller board O?

3. There is no jumper from Y or Ylo to O as the directions say but it looks like you're only supposed to do this on non HP single stage systems. For two stage systems, it says to connect Ylo to O but doesn't specify if this is also for non-HP systems.

4. The LED indicates initial airflow of 600 CFM and then jumps to 1200 after about a minute. It seems like the first stage is always being bypassed. Could this be because the first stage is hooked to Y and not Ylo? What is the purpose of hooking the second stage to the BK/TWIN?

I know when the guy was here, he talked to a guy at Trane for like an hour making sure the setup would work with the stats I have. They're Aprilaire 8570 if it matters.

Thanks for your help.

 

[mark beiser]

Since it is a heat pump, he needs to connect O from the thermostat to O on the furnace control board, or Comfort-R will not work in the cooling mode. The way it is wired now it will do 50% airflow for 1 minute then ramp up to 100%.

The Ylo/Y to O jumper is only used with straight cooling.

Basicly you want to insure that 0 on the furnace control board gets 24v to it when in the cooling mode, but not in the heating mode.

The rest of the wiring is correct for an XL16i, provided the W14 jumper is cut on the control board.

To get the 1st stage airflow Trane wants for the XL16i, they have 1st stage connect to Y on the control board with no power to BK. This causes the blower to run at a maximum of 80% of 2nd stage airflow.
When 2nd stage calls, it powers the BK terminal, wich causes the blower to ramp up to 100%.

The W14 jumper connects BK and R together, so it has to be cut for this to work.

Since it is jumping from 600 CFM to 1200 CFM on a first stage call for cooling, I would bet that the W14 jumper has not been cut on that unit.

[Edited by mark beiser on 06-20-2006 at 12:21 AM]

 

[ellud]

Mark,

Thanks for the quick reply. So you're saying I need to hook up the O from the stat and the HP to the O on the furnace board? But why is the first stage being bypassed? What is the BK/TWIN terminal?

Thanks,

Ron

 

[mark beiser]

Mark,

Thanks for the quick reply. So you're saying I need to hook up the O from the stat and the HP to the O on the furnace board? But why is the first stage being bypassed? What is the BK/TWIN terminal?

Thanks,

Ron

Yes, O from the stat and HP need to connect to O on the furnace control board.

On the XV80, the airflow when Ylo is energized is 50% of when Y is energized.

Since the 2 stage scroll compressors 1st stage capacity is 67% of 2nd stage, Trane decided that 50% airflow is to low for 1st stage on the XL16i.

The solution was to utalize what is normally a dehumidification mode.
If you take power away from the BK terminal while Y is energized, the blower runs at 80% airflow, so for 1st stage cooling the blower is run at 80% by powering Y with no power to BK.
When the thermostat calls for 2nd stage cooling, it powers BK, wich causes the blower to ramp up to 100%.

Since the W14 jumper on the board connects R and BK internally, the jumper has to be cut for this to work.


On that note, the BK jumper should not have been cut on your other system. Since it is a 2.5 ton system, the comfort R ramping should be 500cfm for 1 minute, 800 cfm for 7.5 minutes, then 1000 cfm until the call for cooling ends. Because the W14 jumper was cut on that system, it is only running at 80% of the airflow it should be at each point in the Comfort-R profile.
To fix it, install a jumper wire between R and BK on the furnace control board.

 

[ellud]

OK, so how do I get 2 stages out of the XL16i? If the first stage is 67% of the total, I basically have 2 tons of cooling for the first stage and 3 tons for both. Correct?

For Comfort-R to work, I need 50% airflow for the 1st minute. The air handler is set to a 3T system at 400CFM/Ton. When the stat calls for first stage of cooling, I should get 480CFM because of the request for Y and not BK because 80% of 50% of 400*3 = 480CFM. If the first stage is 2 tons, I would need 400CFM for the 50% part. I guess this is close but my first stage is giving me 600 CFM. I don't see the 80% part. It goes right from 50% to 100% or 600CFM to 1200 CFM. After that first minute, the air handler should go to 960CFM. This is too high for 2 tons. But still, I'm seeing only 600 and 1200 CFM. Is this because the O terminals aren't hooked together? Maybe I'm over analyzing this and hopefully I'm missing something.

I don't see how this could ever work right in a Comfort-R mode. Since the HP is set up for 2/3 capacity and the air handler delivers 50%. I'm getting a bad feeling about my investment.

BTW, the humidity levels in the house never get below 58-59% on either floor.

Thanks again,

Ron

 

[mark beiser]

Like I said, O needs to be hooked up for Comfort-R to work.

The W14 jumper needs to be cut in the furnace for the XL16i.

Until that is done, your system will not run in 1st stage, it runs 2nd stage only, and doesn't do the Comfort-R ramping.

The furnace with the XR14 needs to have a jumper installed between R and BK.

 

[ellud]

Mark,

Thanks again. The W14 jumper is definately cut but the O connection is not made. If I recall correctly, the motor was still doing just 50/100% and skipping the 80% point. I'll do that tonight when I get home from work and add the jumper on the other furnace.

Sounds like I won't get optimum airflow on the first stage. The actual 50/80/100 points are 480/768/960 CFM wheras the optimum points would be 400/640/800 for 2 tons. I don't know if this should be a big concern or not. My first guess is no.

So how does the staging work in heating mode then? Does the blower run at 50% for 1 minute, then 100% after that? Does the air handler run a different profile when the O connection isn't made? That's probably what's happening now since the O terminal isn't connected.

Thanks again,

Ron

 

[mark beiser]

With the heat pump in the heating mode, the blower will run 50% for 1 minute, then ramp up to 100%.

In the heating mode the indoor coil basicly becomes an undersized condensor coil, so it needs all the airflow it can get.

 

[ellud]

Mark, thanks again for the help. I hooked up the O connection to the furnace board and now all the setting seem to working like they should. I get the 50/80/100 points where they should be and when I drop the temp request, the blower kicks up accordingly. I went to the outside unit to listen to the compressor when the second stage kicked in and the only thing I could notice was a slight "gurgling" sound. The fan didn't change speeds at all. Is this normal or should I be able to notice something?

Also, made the jumper on the other unit and it's running correctly.

ron

 

[mark beiser]

There isn't much difference in the compressor sound between 1st and 2nd stage, and no difference in fan speed. The fan does change speed based on the outdoor temperature though.

Glad its all sorted out now.