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Thread: do I have 2 stage systems?
04-02-2005, 12:34 PM #1Regular Guest
- Join Date
- Feb 2003
Hi folks, i had originally posted a question in the thread single stage or 2 stage thermostat with XV80 But in order to keep from hijacking his thread completely I'll post here with my specifics and hopefully some folks will be able to send me in the right direction.
I"ve been in this house almost 2 years now. It has 3 trane XV80 systems. And each is wired or setup a little differently so I hope you don't mind the length of this question and the amount of info in it
Over a year ago I asked the HVAC guy doing my regular maintenance if these were 2 stage systems and can I get a 2 stage stat for them. He told me in no uncertain terms that no, they were not. But I now think he may be wrong.
Smaller system for the bedrooms upstairs has never worked well enough to make me happy, either with heat or AC as the thermostat calls for either, and it comes on LOW and nothing happens perception wise for a while, and then after the timer kicks it into HIGH (since there is no 2 stage stat) the temp quickly overshoots the setpoint and stops. So the temperature swings up there are really out of control. I've done a lot to improve it from what it was by adding an extra layer of attic insulation, moving the thermostat from the shared hallway into one of the bedrooms, and adding a return air vent to the most uncomfortable of the bedrooms. But it's still not "fixed" and all these little things are starting to add up in cost, though the HVAC company likes me as I keep paying them money! They have been very helpful and friendly and always come in right at their estimates for the little jobs, but don't seem to be very good at suggesting something to fix my problem, only happy to do whatever I ask them to do.
Upstairs air handler/gas heater unit has a model number of "TUD080R9U3H5" and they all have the same White Rogers controller in them with a model number of "50A51-507" The W1 and W2 connections are bridged together which as I understand it is what you do when you have a 2 stage furnace connected to a single stage stat. Would there be a W2 and a Ylo connection on the board if it wasn't a 2 stage furnace?
Then there is the question of the outdoor unit, for 2 stage cooling the outdoor unit needs to be 2 stage too correct? The outdoor unit on that system is a trane XL1200 model number "TTX024C100A2" At this moment there is a 3 conductor cable running to it for controlling it, but there are only 2 wires connected inside the furnace (I haven't opened up the outdoor unit to look to see what connections are available in there yet) I would need to connect the 3rd wire to the Ylo to make that work?
I have a problem with this though. If the outdoor unit isn't connected up to be 2 stage, then how can the indoor unit run the fan at a lower than normal speed for a while and then switch to a high speed? Wouldn't it have to also adjust the output of the outdoor unit? If you just run the fan at a lower speed and keep the outside unit at the same output then wouldn't it freeze up the coil or cause other problems?
So that makes me think that either it is single stage and just runs the fan at 2 different speeds, or it wasn't hooked up properly in the first place, which is quite possible.
My downstairs unit is larger, the mode number on the XV80 airhandler is "TUD080R9U3H6" and the outdoor unit is a XL1200 "TTX036C100A1" the white rogers controller inside is the same, and also the 3rd wire to the outdoor unit is not connected and the W1 and W2 are bridged together with no connection to the Ylo at all. Is this also a 2 stage system wired for single stage?
Lastly the third system is for the added on family room, it's the same models as the downstairs system but is wired a little differently. To my mind it's actually wried wrong... These are all gas fired systems and so don't use the "O" connection at all which is my understanding for the reversing valve for a heatpump system? But on that system the Y and O connections are bridged, NOT the W1 and W2, the W2 is not connected to anything. Also the R and the BK connections are bridged which I've not seen on any of the others. Again the 3rd wire to the outdoor unit is not connected. Makes me think almost that someone meant to bridge W1 and W2 but didn't look carefully at the board?
Sorry for 3 different systems and lots of questions But I hope i've supplied enough info for you to know what I've got and if it can be improved with some 2 stage thermostats!
04-02-2005, 01:58 PM #2
The newer XL80 and all XV80 furnaces are 2 stage and you can drastically improve your comfort with a good 2 stage thermostat.
04-02-2005, 02:17 PM #3
First off, both of your furnaces are 2 stage heating. Since you have single stage thermostats, the W1 and W2 connections need to be jumpered together.
When you get a call for heat the furnace will run in low fire for 10 minutes then kick up to high fire untill the thermostat is satisfied.
Provided you have enough conductors in the thermostat wire, it is very simple to change over to true 2 stage control, but you will need 2 stage heating thermostats.
The XL1200 outdoor units you have are 1 stage cooling and only need 2 conductors for the control wiring.
The blower timing for the cooling mode may be set up for Comfort-R, wich is highly recommended.
With Comfort-R enabled on the furnace control board, when the thermostat calls for cooling, the blower will run at 50% for 1 minute. This allows the coil to get cold faster to help with latent cooling for humidity control.
After 1 minute, the blower ramps up to 80% for 7.5 minutes. This allows for greater moisture removal due to the colder coil.
After 8.5 minutes of total run time, the blower kicks up to 100% untill the thermostat is satisfied.
The indoor coil needs to have a TXV installed if you are using Comfort-R or you could have problems with flooding the evaperator coil and slugging the compressor. If the installing contractor matched up the equipment properly, you should already have TXVs in the coils.
To enable Comfort-R, dip switches #5 and 6 need to be in the on position on the control board. The rest of the dip switches positions are dependant on the equipment selection and desired airflow. There is a chart on the blower access door for all the settings.
All three systems should by wired the same.
Y from the stat to Y in the furnace to Y to the outdoor unit(yellow wire).
R from the stat to R in the furnace.
Common in the stat(B if it is a Trane stat, C if other) to B in the furnace to B in the outdoor unit(blue wire).
G in the stat to G in the furnace.
W1 in the stat to W1 in the furnace.
W1 in the furnace jumpered to W2 in the furnace.
The jumper between R and BK is built into the control board in the furnace, so you don't need to add a jumper wire.
For Comfort-R to work, there needs to be a jumper between Y and 0 in the furnace.
No conductors should be going to Ylo.If more government is the answer, then it's a really stupid question.
04-02-2005, 10:58 PM #4
The outdoor unit (cooling) has a 'two-speed fan'
it is not a 'two-stage unit'
The speed it operates is based on outdoor temperature.
It does not require any extra wiring from the stat or furnace, this function is built into the unit. Off the
top of my head, I think the temp it changes over is 75 degrees outside(might be 80, I can't remember at the moment). Above this temp, the outdoor fan runs at a higher speed. Lower than this temp, the outdoor fan runs at a lower speed.
When you asked your maint tech if the systems were two stage, he may have thought you were asking if the cooling units were two stage and wether you needed a two stage cooling stat. In this case, he was correct. You do not have a 'two-stage cooling unit' and it does not require a two-stage cooling stat.
You do, however, have 'two-stage furnaces'.
They do not 'require' a two stage heating thermostat, but
two stage heating thermostats would increase the comfort level and actually increase the effeciency of your furnaces. (long story but furnaces' effeciency increases the longer they run.)
You could try running all your furnaces on just low speed.
You already have one system set up for just low speed heat (the one with W2 not connected)
We have several of our systems set up with just the first stage heat hooked up. When asked how their heat has been,
all the customers give their heating high marks.
Without doing a load on your house, I can't say wether this will work for your system but you can try and see how it turns out. Least it will be a cheap experiment.
Turn power off to unit, ground yourself to discharge any static electricity, remove jumper between W1 and W2
(if you dont' understand these instructions then get a tech to do it. I dont' want to be responsible for you getting hurt or damaging your unit).
This is going to be a bad time of year to say wether or not it will be OK for the long run since we are starting to get over the heating season. You'll find out wether you NEED second stage heat once we get into the fridged weather again.
What did you mean by...
'...never worked well enough to make me happy, either with heat or AC'
Explain why your AC was not comfy. What did you have the stat set for, what temp did it maintain? What was the outdoor temp when it did not maintain the temp you asked for?
Extend to others the grace that God has given you.