Wiring of my existing thermostat and converting to nest.


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Old 08-18-15, 10:05 AM
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Post Wiring of my existing thermostat and converting to nest.

Hello,

I don't think Nest thermostat is compatible with my system. However, I am curious what my existing wires do. Any help to clarify it will be greatly appreciated!

I live in a condo with a common central AC and heating system on the roof. I have a Trane thermostat currently in my condo. The pictures posted in this thread show what wires are connected to my existing thermostat: G/B/R/Y/O. I have researched a little but still not sure what they do. My electrical box does show a switch for heat pump to turn on/off the thermostat. My questions:

1) What does each of those wires (G/B/R/Y/O) do?
2) For the connectors that are not used (F/W/X2), what do they do and why I don't need them?
3) If I still want to connect them to the Nest thermostat (posted picture of the wiring options), which one will go to which one?

My existing wires are stranded. It is not compatible with Nest, which uses single wire. I may need to use a transformer to convert the voltage, if I want to use Nest. I am just curious what I have bow and what I may need to do (wiring wise) if I want to use Nest.

Thanks for your help!

-Justin

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  #2  
Old 08-18-15, 12:11 PM
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A Nest is compatible with your single stage heat pump.
Old B is C on Nest. The remaining terminals are the same.

G-fan (G)
R- power (RC)
B-common (now C)
Y- compressor (Y1)
O- reversing valve for cooling (O/B)

Not in use...

F fault light
W -electric heat strips
X2 emergency heat strips
 

Last edited by Houston204; 08-18-15 at 12:55 PM.
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Old 08-18-15, 05:37 PM
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Ah, thanks! New to doityourself.com and I am surprised how quickly someone is willing to land a helping hand. :-)

If I can ask a couple of more questions:

1) i understand G and R are used (turning on/off fan and the power feed into the thermostat). Since I can get both cold air and hot air through my existing thermostat. How are B/Y/O are used to control that? I did notice my existing thermostat has a switch to turn on the cold or the heat.

2) My current wire is stranded. Based on what I read, I may have high voltage lines feeding into my existing thermostat. Nest uses low voltage and single wires. Since you mentioned my system is still compatible with Nest, what should I do if I want to connect them to Nest? (Assuming this is the right thing to do, I found a relay/transformer that may be useful for converting the voltage. How do I wire it to re-level the voltage? Here is the part: Aube RC840T-240 On/Off Switching Electric Heating Relay with Built-in 24 V Transformer)

I probably should measure if my wires are indeed high voltage wires with a meter. I do need single wires instead of stranded wires.

I hope I explained the situation reasonable clear. Thanks in advance for any help that may be offered!

-Justin
 
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Old 08-18-15, 05:48 PM
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R= 24vac to the thermostat. Everything gets connect to the R terminal to work.
G= blower fan When you connect G to R.... the blower starts.

Y= A/C compressor. When Y is connected to R..... the compressor runs. You have a heat pump so only powering the Y terminal will put the system in heat mode.

O= reversing/cooling valve. When O gets connected to R..... the valve activates and the system is on cool mode.

So everything switches to R to operate.

I see larger stranded wiring that would suggest hi voltage switching. With the thermostat removed use an AC voltmeter set to at least 120v and check from R to Y.

Is there a model number on the back of that Trane stat ?
 
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Old 08-18-15, 06:11 PM
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Thanks for explaining it to me! That makes sense. How about B-Common (now C)? What does it do?

I will check the voltage soon as well as the model number, probably this weekend.

Let me phrase it as an open question (instead of assuming using the relay/transformer) - how do I connect wires like this to Nest?

Thanks again,

-Justin
 
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Old 08-18-15, 06:19 PM
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Let me phrase it as an open question (instead of assuming using the relay/transformer) - how do I connect wires like this to Nest?
If it's a high voltage (120v) stat..... you can't...... at least not directly.

You'd need at least a Y relay, O relay, G relay.

The C common wire runs the display section instead of batteries.

I'm a little confused..... you live in Mass. and you have a heat pump. Does it keep you warm enough ? Usually in a cold northern climate you would need some type of back up heat.... whether it's an electric reheat coil or a gas furnace.
 
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Old 08-18-15, 06:43 PM
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Thanks for the reply and explain the B-Common (now C). So it is powering the display of the thermostat? Why it couldn't use R?

So I just need 3 relay for Y/O/G? Can I use the part mentioned in my original post to do the job? A little more what the process may take to hook it up with Nest will be appreciated.

My condo does have a backup generator just in case the power is gone. Maybe that's why there is no need to backup heating.

-Justin
 
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Old 08-18-15, 07:36 PM
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A back up generator is a wonderful thing but not quite what I was after.

A heat pump system is only effective down to a certain temperature and if the outside temperature goes below that point you don't have enough heat. Also, when a heat pump system defrosts..... it runs the system in air conditioner mode which means it takes heat out of the house to defrost the outside unit. This means there will be cold air blowing inside the house.

That unit you linked to is for 240v electric heat. You'd want something to run on 120v and you would still need two additional relays.

Thanks for the reply and explain the B-Common (now C). So it is powering the display of the thermostat? Why it couldn't use R?
R is one side of the 24v transformer and C is the other side of the transformer. Just as an example only.... consider the R as + and the common as -.

Once we determine if you have 120v controlling there.... I'll draw up a diagram for you of how to wire your stat into your system.
 
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Old 08-18-15, 07:42 PM
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Think of 24 volt common as the second wire feeding a desk lamp. If you cut 1 of the 2 wires between a lamp and the wall you will not have a complete circuit and a lamp wouldn't work.

If you post the model number of that thermostat we can look up the operating voltage.

Geothermal heat pumps are fairly common in condominiums over 6 stories in my neck of the woods and they almost never have heat strips around here.

I have never seen a high voltage application with conventional heat pump terminal labels. I would be interested in looking that model number up.
 
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Old 08-18-15, 08:09 PM
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Thanks for the replies from PJmax and Houston204. Sorry if I asked some dumb questions...

I understand R and B-Common now. Thanks!

I will measure the voltage this weekend and see if I can find the model number on the thermostat.

A little bit more information: I just moved in to this condo and am learning what they have. It's a newer building and they have good AC and heating unit on the roof, based on the feedback from my inspector. I have two thermostats in my condo along with two "boxes" below them (I should take a picture of it this weekend). I had to put air filters to the boxes. I haven't gone through the winter here yet but I assume two heat pumps should be able to heat the room... Again, I will take more pictures this weekend and hopefully it will be easier to explain what I mean.

Thanks again for all the suggestions so far!

-Justin
 
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Old 08-23-15, 07:39 AM
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Hello,

I did my homework and here is what I got:

1. The voltage is 33 VAC, measured between R and Y.
2. Here are three pictures of 1) the model number inside the cover of the thermostat, the unit under the thermostat, and the picture of both the thermostat and the unit. By the way, what is the unit under the thermostat? I know I need to replace the air filter regularly but I don't know what it is exactly... I think I put the air filter at the right direction but it there a general rule that the air is flowing into the unit or out of unit.

I really don't know what I got but I did learn a lot so far in this thread. And thanks again for any help you can offer.

-Justin

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Old 08-23-15, 09:27 AM
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That is great news. So the Nest thermostat is compatible with your low voltage system.

Refer to post to when connecting the new thermostat.
 
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Old 08-23-15, 10:34 AM
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I cannot make out the model number on that closet model Trane unit.

The length of the model number and the fact that it appears to say factory charged with R22 might indicate that it is a Geothermal unit.

A closer picture of the model number would help verify this.

I have seen Trane Geo units but that appears to be smaller than I would have expected.

Can you hear a much louder hum when the system is cooling than when only the fan is running?
 
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Old 08-23-15, 11:57 AM
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Sorry if the picture is not large enough. The model number inside the thermostat form the picture is T8411R. I searched for it and it seems like it is under Honeywell's model:

https://www.climatemaster.com/downloads/69-1486.pdf

The manual above seems to show a different marking of the letters for the connectors (G/C/R/W1/Y on the left and L/W2/E/B/O on the right), vs. the one I have now (G/B/R/None/Y on the left and F/W/X2/None/O on the right). The outside looks the same except for the Honeywell vs. Trane brand marking. Are they the same?

New set of questions for installing the Nest thermostat:

1. The wires that are used currently is stranded. If I want to connect them to Nest thermostat, they need to be single wire. How do I convert them?

2. I searched the power requirement for the Nest thermostat and it shows the range of 20-30V AC. Is it okay the one I have now based on what I tested is 33V?

3. Here is the picture of the closet unit. The model number I can see is (long one): GETA01211D011S11D00000010480LMDDD120 and the serial number is W05C13605. Can you tell me what is the closet unit used for?

Thanks,

-Justin

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Old 08-23-15, 12:42 PM
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You can use the stranded wire if it will fit in the nest terminals. In not... then you will need to wire nut on short solid wire jumpers.

The voltage you have is fine for the nest.
The unit in the closed is the air handler where the blower blows air thru a hot or cold coil and into the room.
 
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Old 08-23-15, 01:06 PM
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Thanks!

Yes, the stranded wire is not fitting into the Nest terminals. I will buy wire nuts and short solid wire jumpers to connect them. And, as a clarification, I will connect my existing wires to the Nest through the following configuration:

G-fan (to Nest G)
R- power (to Nest RC)
B-common (to Nest C)
Y- compressor (to Nest Y1)
O- reversing valve for cooling (to Nest O/B)

Please let me know if I am missing anything. Thanks again.

-Justin
 
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Old 08-23-15, 05:12 PM
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You are correct with the wiring.
 
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Old 08-29-15, 05:44 PM
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Hello,

I have connected the Nest thermostats (both of them) following the suggested wiring connection. Everything went well but one problem: it blows hot air in the cold mode, and blows cold air in the hot mode. What should I do?

I set it to the hot mode and set the temperature higher than room temperature to trigger the blower. It blows cold air. Clearly the temperature won't go high to stop the thermostat I did this to cool my room after I heated it up in the cold mode. Any help will be appreciated!

Thanks,

-Justin
 
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Old 08-29-15, 06:27 PM
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I believe I fixed the problem! Just followed this link on Nest site to correct the problem:

https://nest.com/support/article/My-...-to-be-heating

Thank you ery much for your help! I can't believe the quality of the suggestions I got here vs. how the electrician didn't even bother to test the voltage and gave up on installing the thermostat. :-)

Thanks again!!!

-Justin

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Old 08-29-15, 07:09 PM
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Yup.... you had to change the O voltage status.

Awesome you've got it working correctly. Thanks for letting us know how you made out.
 
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Old 08-29-15, 10:40 PM
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Thanks again for your help!

If I can ask another question: one of the thermostats at time does't blow cold enough of air. What I mean is it may blow cold air and suddenly, just blows the air and a little bit warmer. I would need to turn it off and back on to make it blow cold air. This happens before and after I replaced the thermostat. What could it be and what should I do?

Thanks,

-Justin
 
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Old 08-29-15, 11:08 PM
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In order to get cold air from the system.... the compressor and the condensor fan need to be running. When you lose cold air check and see what's happening outside at the compressor unit. Check the large copper line, usually insulated, it should be ice cold.
 
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Old 08-30-15, 06:36 AM
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The manual WSHP-IOM-2 in the picture indicates that this is a water source heat pump (geothermal).

The compressor should be in the closet with the air handler if this is the case.
The suction line wouldn't be visible outside of the cabinet.

Probably only see water in, water out and a drain or 2.
400 psi max water pressure would be alarming if I ever saw it.

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Old 08-30-15, 09:28 AM
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Good morning,

Thanks again for looking into the problem with me.

Let me attach a picture of the unit. I opened it and all I could see is this big box and a black pipe next to it. I did saw the previous owner/installer left the installation/owner manual right next to it on the floor inside the opening. I wonder if I can provide any additional information?

I browsed the document quickly. I wonder if the refrigerant needs to be refilled? The only symptom I experienced so far is on and off cold air. For example, when I came back last night, both of them are not blowing cold air. I turned them off before bed time. This morning, I turned one back on and it is blowing cold air. The other one is blowing room temperature air.

Again, and suggestions will be greatly appreciated. :-)

-Justin

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Old 08-30-15, 10:04 AM
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http://www.trane.com/Commercial/Uplo...-prc013-en.pdf

Servicing a water source heat pump is a little more involved than most heat pumps.
The water flow should be checked before the refrigerant level is checked.
I do not see the water pressure drop chart in this manual, only the corrections made for antifreeze and hose kits...
 
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Old 08-30-15, 11:04 AM
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Thanks Houston204. What do you recommend the next step?

I have sent a note to the condo management office and asked them about it (unreliable AC). I don't know if they are responsible for it or me...

I just checked again. One heat pump is blowing cold air and the other is blowing room temperature (and maybe a little warmer air because of running the heat pump?). The one is not blowing the cold air used to be the consistent one blowing cold air. I am a bit puzzling now.

Any trouble shooting suggestions will be appreciated!

-Justin
 
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Old 08-30-15, 11:54 AM
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A visual inspection in the service panel for swollen caps, melted wiring, verify that you do not have a pan under the unit that is full of water and tripping a float switch. Is the air filter and evaporator coil clean?

Ice should not be present anywhere?

The inlet water pipe should be 7 to 10 degrees warmer than the outlet.

Pete's plugs should be present at the inlet and outlet water pipes if a Geo tech is to properly check water flow.

He will also need the pressure drop chart found in a manual for that unit.
 
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Old 08-30-15, 07:14 PM
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I turned the thermostat to the heat mode and it blowed the same level of air as in the cold mode. I was wondering the wires into Nest thermostat were not hooked up properly, particularly the Y1. I disconnected them all and connected them again. It seems to be working now. I hope it will continue - will keep an eye on it.

Thanks again for providing the suggestions. PJMax and Houston204: you two are great! I am wondering why you spent time helping people like me here? Especially, you really read what I wrote as a newbie, and tried to explain it with the language I can understand. It takes some effort to do so... Appreciated!

-Justin
 
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Old 08-31-15, 07:07 AM
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Ah... Spoke too soon. When I woke up this morning, one is blowing cold air and the other is regular air. I need to look into it again. Journey continues...

-Justin
 
 

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