Couple of questions about installing a new digital thermostat


  #1  
Old 12-17-05, 12:18 PM
zilla31
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Couple of questions about installing a new digital thermostat

Ok i've got a bit of an older house w/ baseboard heating (water) and my "old" thermostat just blew (wouldn't properly spark to turn on/shut off so it was always on and heating the heck out of the house and costing me a fortune in the process).

Currently i have side-by-side thermostats for heat and a/c but was wondering if (since i have to replace the heat one anyways) i can get a fancy new digital one to replace both (both current thermostats are those old "spin" style... the heat one (which i've just taken off the wall since it's broken) only has 2 white wires to it).

essentially i have 2 questions then: 1) can i get a digital thermostat to replace BOTH the heat (broken) and a/c thermostats i have sitting next to each other, and 2) how can i be sure i install the new heat one properly knowing i only have 2 white wires from the wall?

THANKS!!!

ps it's freezing in here so please help
 
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Old 12-17-05, 01:17 PM
zilla31
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ps is this question in the wrong forum? sorry (noob). if so mr. moderator can you move it for me please?
 
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Old 12-17-05, 04:37 PM
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Thermostat

Since your question pertains to a hot water heating system, you are in the right forum.
Most digitals will work for both heating & cooling. You need to connect one of the heating wires to Rh & the other to W on the new thermostat. It makes no difference which wire goes to which terminal. If your boiler has zone valves with 3 wires to each one, you have heat motor type zone valves. Some digitals are not compatable with this type of zone valve.
 
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Old 12-17-05, 04:55 PM
zilla31
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hmmm - i checked my zone valves (there are 2) and they have 3 wires coming into them (even though one of the wires is kind of 2 really thin red ones making it look sort of like 4 are going in).

so how do i make sure i get a digital compatible w/ my setup? is there anything to know about my A/C to determine if i can use ONE digital thermostat instead of the two i currently have?
 
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Old 12-17-05, 05:19 PM
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Digital Thermostat

Nearly all A/C systems use three wires (Rc, Y, & G). You will have to look at the installation instructions which come with the thermostat to see if it is compatable with heat motor type zone valves. Honeywell makes a thermostat (T8775) which I know is compatable. You will need to install the resistor which comes with the thermostat. Before you buy a thermostat look for a name on the zone vavles. If they say Taco (pronounced Tay-co) you will definately need the resistor. They look like this but not all are the gold color. http://taco-hvac.com/en/products.htm...t_category=112
 
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Old 12-17-05, 05:41 PM
zilla31
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the zone valves i have are honeywell sparco powertrack motorized zone valve operators

kind of like these but not exactly:

http://www.plumbingsupply.com/zonevalves.html

that thermostat you pulled up for me is on the money except for one thing - i'd like to get one that will operate a daily schedule (conservation).

thanks a ton for your help...

ps i may have discovered another problem though - i've pulled the thermostat off the wall but the heat in my upstairs "zone" (controlled by one of the zone valves) is ALWAYS running. I thought it was the thermostat but since it's STILL running w/o the thermostat even hooked up - i guess it's not that? (regardless i'm still changing my thermostat to a combo so no wasted effort here).
 
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Old 12-17-05, 05:55 PM
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Thanks for the link

That zone valve is not a heat motor type so you should not have to worry about compatability. Another caution about thermostats: Make sure you do not get one which requires a "common" wire. Most battery powered thermostats do not.

Upstairs zone: Label & disconnect the wires to the zone valve & give the pipes 1/2 hr. or so to cool. If they do not cool, the zone vavle is stuck. If they do, there is a wiring problem somewhere. According to the site to which you linked, the operator can be replaced without opening the system.
 
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Old 12-17-05, 06:20 PM
zilla31
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ok i'll try that to diagnose the problem w/ the operator. could be the operator for the upstairs zone is stuck/bad/mis-wired.

thinking ahead to the new thermostat though - i have 2 white wires coming out of the wall for the heat, and i'm supposing 3 for the A/C, so that means i'll be hooking up 5 into the new thermostat right? and all we've come up w/ for me to be sure and look for when buying one is to make sure and get one w/o a "common" wire (so potentially battery operated)?
 
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Old 12-17-05, 06:33 PM
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New Stat

When connecting the wires, make sure the power is off to the boiler & the A/C. Electronics don't like sparks, no matter how small. Most stats come with a jumper between Rh & Rc be sure to remove it. Connect R from the A/C to Rc, Y to Y, & G to G. For heat, connect one wire to Rh & the other to W. It makes no difference which is which.
The vast majority of thermostats which are battery powered do not require a "common" wire.
 
  #10  
Old 12-20-05, 01:04 PM
zilla31
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Grady -

I picked up a Hunter brand thermostat (model 44550, battery powered) which hopefully will do the trick.

Got it home and realized that i have 6 wires coming from the wall (2 whites that went to the old heat thermostat, and 4 (red, orange, yellow, green) that went to the A/C thermostat. The new digital Hunter thermostat appears to only take 4 wires "in".

I assume this means i need to do some twisting of wires from the wall together (prob the power and ground or whatever?). any help?

as always - THANKS.
 
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Old 12-20-05, 01:07 PM
zilla31
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Originally Posted by Grady
When connecting the wires, make sure the power is off to the boiler & the A/C. Electronics don't like sparks, no matter how small. Most stats come with a jumper between Rh & Rc be sure to remove it. Connect R from the A/C to Rc, Y to Y, & G to G. For heat, connect one wire to Rh & the other to W. It makes no difference which is which.
The vast majority of thermostats which are battery powered do not require a "common" wire.
ps i reread this post and you may have told me what i need (mostly) but what about the old "O" wire that is connected to my old A/C thermostat? Seems that one is not used according to your instructions... right?
 
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Old 12-20-05, 06:29 PM
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Question "O" wire?

Normally the only time one would see a wire connected to an "O" terminal is for a heat pump.
Please list the wire colors & to what terminal they were connected on the old thermostat. You may have a heat pump just being used as A/C only.
If you can provide such, a make & model of the outdoor A/C unit may also be helpful.
 
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Old 12-20-05, 06:47 PM
zilla31
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sure (and continued thanks for your help).

the heat thermostat (as you know) only had 2 white wires attached.

the A/C thermostat had 4 coming from the wall, Orange (connected to "O"), Red (connected to "R"), Green to "G", and Yellow to "Y". I used the little tap markers provided w/ the new digital thermostat (and your instructions) to tape them as follows:

R -> Rc
Y -> Y/Y1
G -> G
O -> O/B

I haven't hooked anything up yet, just marked the wires and removed the old thermostats.

I'll have a look outside tomorrow and let you know the make/model of my outdoor A/C unit.
 
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Old 12-22-05, 06:34 AM
zilla31
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looks like i have a TRANE XR12 (http://www.trane.com/residential/pro...ners/XR12.aspx) which is a combo heat pump and a/c? might explaing the "O" wire. can i just leave the "O" wire diconnected?

THANKS! (we're almost there).
 
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Old 12-22-05, 08:24 PM
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Complete model number

After a little research, I find the XR12 could be either a heat pump or plain A/C. If you can provide a complete model number from the data plate on the unit, I will be able to find out which it is for sure.
Another help would be if you can find out where that "O" wire goes. Sorry to be such a bother but I don't want you frying something.
 
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Old 12-23-05, 07:44 AM
zilla31
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grady the absolute LAST thing you're being is a bother - you're really helping me out here so keep the questions coming so you can help me get this right...

the XR12 model number (it's a long one) from the data plate is:

2TTR2036A1000AA

you second question was where the "O" wire goes... i'm not 100% sure what you're asking here but the orange wire came out of the wall and went to the "O" marked screw on the OLD thermostat (even though the old thermostat had nothing to do w/ heat, only A/C).

On the NEW thermostat, there is a "O/B" screw that i assume it will go to (but i haven't hooked anything up yet - waiting on you).

THANKS!!
 
  #17  
Old 12-23-05, 11:53 AM
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What Grady's trying to ask is where does the other end of that O wire go? Like on the air handler controller, what terminal is it hooked to?
 
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Old 12-23-05, 12:32 PM
zilla31
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ok on further investigation those wires (from the thermostat) go to an air handler in my attic (also a trane, model TWE036C14080). looks like it's a combo A/C slash heat pump that's being only used for A/C.

I took the access panel door off and it's pretty much impossible to tell where the orange ("O") wire goes (there's a series of twisted together wires going through various checkpoints etc.).
 

Last edited by zilla31; 12-23-05 at 12:48 PM.
  #19  
Old 12-23-05, 12:49 PM
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ps - is it not sufficient to just hook the orange wire up to the NEW thermostat "O" terminal just like it was on the OLD thermostat?
 
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Old 12-23-05, 06:27 PM
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Orange Wire

I THINK hooking the orange wire to the O terminal on the new stat would work ok but I'm not positive. What make & model T-stat did you get. I would like, just for my own curiousity, to see if I can find out anything on the manufacturer's web site.
 
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Old 12-23-05, 07:55 PM
zilla31
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it's the hunter brand "auto saver 550". i'll prob try and hook it up tomorrow... even though i think i have a bigger problem ultimately (the heat has still been running upstairs whenever the boiler is on even WITHOUT ANY THERMOSTAT HOOKED UP!

I think maybe one of the zone valves (i have 2 - 1 upstairs, 1 down) is screwed up and in an always "on" position. Basically i'm having to control the heat in here by shutting on/off the boiler.

W/ your help though i can at least get past installing the new thermostat - then i can start asking you guys about the greater problem once we've got that handled
 
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Old 12-23-05, 08:56 PM
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Hunter

From what I can tell, it looks like you could connect the O wire to the O terminal. Start with the "normal, O, B switch in the normal position. You may end up having to move it to the O position. It might be worth a call to Hunter for better info. Personally, I don't see why you could not connect the orange wire & the Y wire to the Y terminal. This should energize the reversing valve when ever there was a call for cooling.
 
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Old 12-24-05, 09:42 AM
zilla31
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ok i hooked it all up and programmed it. first thing i noticed is that if i set the fan selector to "on" the fan WILL come on (A/C), but if it's on "auto" it won't come on even though the temp in here is 78 and the desired temp is set to 65.

** PS i found in the instruction manual the info for the "O" wire (help me decipher):

Furnace or Heat Pump selector (NORMAL - O - B switch):

The factory position for this switch is in the NORMAL position. Leave it in this position if you have ANY system that uses gas, oil, electric, or hot water heating.

If you have a single-stage Heat Pump (no aux or emergency heat source), then slide the switch to the position that matches your Reversing Valve type. If your heat pump system has a "B" wire, slide the switch to "B" for your reversing valve that activiates in HEAT mode. If your heat pump system has an "O" wire, slide the switch to the "O" for your reversing valve that activates in COOL mode.
by the first paragraph it seems i should leave it in the NORMAL position, but by the time i finish reading the second paragraph, seems like i should set it to "O"? Right now it's in NORMAL.
 
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Old 12-24-05, 10:19 AM
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Clear as mud

I know what you mean. When I read the instructions, I was not totally clear on them either. That is why I was thinking of connecting both the O & Y wires to the Y terminal. By doing this, the reversing valve would switch to the cooling position whenever there was a call for cooling. I'm going to ask one of our heat pump gurus to look at this thread & see what he thinks.
I don't know how long you tried the fan in auto but many air handlers have a delay in the fan to allow the refrigerant to actually start cooling before they bring the fan on. This delay is generally on the order of 30-45 seconds.
 
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Old 12-24-05, 10:27 AM
zilla31
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yeah it's weird - if i have the stat in COOL mode then the fan WILL come on automatically by temperature, but not in when in AUTO mode. For the meantime i switched the heat to the "O" setting (based on their instructions) but i'll def wait to hear back from you (in case i need to just twist it w/ the Y).

Grady - THANKS for all your help on this and HAPPY HOLIDAYS partner - you're saving me a fortune i'm sure
 
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Old 12-24-05, 08:13 PM
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I think Grady is on the right track here. Trane heat pumps use O to energize the reversing valve. I would agree with him that in this case, you should put it with the Y wire. Since you are not using it for heat you wont have a problem. Im not sure of the hunter thermostat as I have never seen one. Im sure it will work fine. Did you turn the power off to the air handler before hooking it up?
 
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Old 12-24-05, 09:20 PM
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Merry Christmas everyone!

Ok, Grady asked for my help! :-)

Ok, The unit you got is NOT a heat pump.

Your model is 2TTR2036A1000AA

2TTR is A/C only, and 2TWR is Heat Pump

air hander is made to do both.

So undo the O wire and forget it even is there.

So

From the A/C

R---red---RC
G---green---Green
Y---yellow---Y


From the boiler.

Rh---red--R
W---white---W
 
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Old 12-24-05, 09:29 PM
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Thanks Jay

Some of the model numbers really throw me & choo-choo is about as bad as it gets. Most of the stuff I deal with uses an A for A/C only & an H for heat pump in the model #.
 
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Old 12-25-05, 08:56 AM
zilla31
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thanks guys a MERRY CHRISTMAS!!! I just took off the stat cover and noticed that the yellow termnial (new stat now) is all brown and fried looking

everything was hooked up just like Grady (and now Jay11J) said except the "O" wire which i've not disconneced and capped off.
 
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Old 12-25-05, 09:00 AM
zilla31
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ps i also noticed that the A/C was running this morning when i woke up, even though the temp in here is 60, and the desired temp on the stat reads 65... (this is with temp switch in AUTO and fan switch in AUTO). ugh.
 
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Old 12-25-05, 09:58 AM
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Zilla

Did you remove the jumper between Rh & Rc?
Where in the heck does this O (presumably orange) wire go? Just from the stat to the air handler?
 
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Old 12-25-05, 10:01 AM
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Oh no..

Well, To be honest, I have not heard many good things about Hunter T-stat. Undo the Hunter and if you need heat does the old a/c stat have heat switch on it?

If yes, then hook up R and W on that stat to get by till you get a new one.

If the new hunter still works (heat). just undo the Rc and Y wire for now.
 
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Old 12-25-05, 10:07 AM
zilla31
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the OLD stat did not have a heat selection at all... it was just for controlling A/C. I ended up gong w/ Jay11J's advice on the "O" wire and just capped it off (going nowhere). did we finally decide if that should go nowhere OR be connected to the "Y" terminal w/ the "Y" wire too?

i think i'm going to trade this Hunter in for a Honeywell here on tuesday (after all my holiday family business the next 2 days)...
 
  #34  
Old 12-25-05, 10:50 AM
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a few choices

You could use the original Honeywell T87F Round thermostats it sounds like you have and just install a new Honeywell Q539-1147 sub base and use only one of the old round T87F Round thermostats and keep the other as a spare. The new sub base has isolation capability (Rh and Rc), what this does is allow your thermostat to use two power source transformers. One from the boiler, and one from the air handler. The sub base has Rh, Rc, W,Y,G. These are the only connections you need. Rc and W for the two wire to heat, and Rc for the red wire for cooling low voltage power, Y for yellow to pull in the contactor for cooling, and G (green) for the fan in cooling.....Done!
Mount the original thermostat that was on the heat side to the sub base after the wires are connected, and write down the anticipator setting somewhere (likely about .4a) and set the other one for the same and put it away as a back up which you'll likely never use. And the tackle the real problem..... the zone valve.
Oh, I believe you can get that subbase at HD but they are white now, you likely have the gold stat which I dont think are made any longer.
 
  #35  
Old 12-25-05, 11:38 AM
zilla31
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hvac - i think i follow you but my wife is really pushing the idea of a "programmable" thermostat to help us conserve.

plus the "old" stats are totally different; the heat only one had just the cylindrical slider (no switches at all), and yes it was gold the second one, used for A/C only) was also a gold round that looked very much like the heat one except it DID have switches for fan ("on" and "auto") and cool ("cool" and "auto").

I think my next action will be to replace the Hunter (which now has that burned out "Y" terminal) w/ a Honeywell digital programmable and hook up all the wires (as labeled) except "O". What do we all think about that?
 
  #36  
Old 12-26-05, 10:40 AM
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programmable

the heat only, is heat only, because the switches are not contained in the thermostat, but rather in the sub base to which the wires are connected, and then the thermostat is connected to the sub base with the three screws of the thermostat. These three screws make the electrical connection to the sub base. Any time you wire a thermostat its best to kill the power to the air handler and the furnace or boiler which ever the case may be. If your determined to go programable, the Honeywell T8602D Chronotherm IV is a nice one that does heat, cooling, and autochangeover, it has a selectable fan switch that can also program the fan during different periods to on or auto, it also does heat pumps, dual or single transformer applications, and you can actually calibrate the temperature sensor to reflect actual room temps if it goes out of calibration. It does alot! You can actually install a sensor outside and have it tell you the outdoor temperature on the face plate and a daylight savings switch .....I have it in my upstairs, although I only use it for heat, it works great. Keep in mind these stats have a 5 minute time delay unless you program it not to ( this is do-able).
 
  #37  
Old 12-26-05, 03:10 PM
zilla31
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ok i'll def look at that thermostat (is this it?):

http://www.store.yahoo.com/air-n-wat...7dayprogc.html

ps - are you familiar enough w/ this stat to tell me what to connect to what based on the thread above (which will tell you which wires i have coming from the wall needing to go somewhere).

pps - you think they have this stat at Lowe's or HD? i'm out of town for a week starting wed so kind of want to get this resolved tomorrow while i'm off work... THANKS!!
 
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Old 12-26-05, 06:47 PM
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zilla31

I still want to know where that 'O' wire travels. The model number off of the air handler might help. I know you gave us the model of the outdoor unit but I'm thinking the outdoor unit may have been replaced at some point in time & the old air handler left in place.
 
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Old 12-27-05, 05:55 AM
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Grady, I gave you the link to the manual on the air handler.. Trane's air handler is made for both.

The honywell t-stat can be found at home depot.. They got the Honeywell Vision t-stat. I put one on for a friend about a month or so ago, and they have been happy with it.

When you do hook it up. Make sure power is killed for BOTH equipements. and remove the jumper wire.
 
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Old 12-27-05, 07:19 AM
zilla31
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ok jay - i'll look for the Honeywell Vision today (that's an ok one to get instead of the T8602D Chronotherm IV?). thanks guys (a ton). heading to st. croix for a 10 day vacation w/ wifey tomorrow so i won't need much heat/a/c there thank God! whatever i can't get done today on this i'll address when i get back (so you guys know i didn't disappear totally).

THANKS!!
 
 

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