Mechanical or electrical device used to control a heating, ventilation, and air conditioning (HVAC) system, or other temperature reliant system.

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Which terminal should be used for a “C” wire when none are labeled “C”? Older electric furnace/heat pump

I have an all electric air handler/furnace connected to a separate AC unit and it is also a heat pump. I've purchased the latest and greatest Honeywell WiFi "Smart" Thermostat and it needs a C wire. ...
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1answer
15 views

Where do I connect my C wire from my thermostat when there are two transformers?

I have a Laars gas boiler that has 3 heating zones. I want to replace the old mercury honeywell tstat on the 1st floor (heat only) with a newer honeywell RTH9580 wifi model. I've taken pictures of my ...
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0answers
18 views

Furnace not working properly with digital thermostat

I have been attempting to use several different types of digital thermostats to replace my old mercury thermostat, however none of them are able to control the furnace properly. All of them are able ...
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2answers
12k views

Should I use 12/2 or 12/3 to wire a 220V electric baseboard heater and thermostat?

When I bought my baseboard heaters, thermostats and 220V breakers I was advised to get 12/3 wire. When I attempted to install the heaters I found that the thermostats, heaters, and even breakers have ...
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2answers
18k views

Why won't my A/C turn on after I replaced the thermostat batteries?

Our thermostat died yesterday, but after replacing the dead batteries with fresh batteries, and confirming the LCD screen was operable, our AC no longer turns on. I have attempted a factory reset on ...
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1answer
190 views

Can I replace this Airwell thermostat?

I am in market to replace my simple A/C control unit with one that integrates with home my z-wave based home automation system. However, before I make the splash and buy a compatible thermostat, I ...
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2answers
44 views

thermostat batteries replaced, AC unit won't start

Came home from work to find no AC. I checked the thermostat and the display was blank. After replacing the batteries and resetting the program, my AC unit never started up. I checked: - The AC unit ...
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1answer
45 views

How to connect a DIY thermostat to the HVAC System

I am building a DIY thermostat similar to this blog. I want to connect it to the HVAC system of my home. How do I do that? I found this post which is very informative but doesn't completely answer my ...
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1answer
298 views

No electricity going to thermostat

Our old thermostat is working but I want to change to a new one (nest thermostat). I have two exact HVAC unit at home. I change one it works but when I change the second one it doesn't work because ...
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1answer
325 views

How can I add a C-wire to a Venstar T5800 thermostat?

I am trying to replace my existing thermostat. My old thermostat has: Rh, W (coming from the heating unit). Rc, Y, G (coming from the AC unit). On the Venstar T5800, I can map as follows: Rh+Rc ...
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1answer
83 views

Replacement thermostat wiring

I have an American Standard heat pump AC. I'm replacing a White-Rodgers manual thermostat (where I move a switch from cold to heat) with a Honeywell RTH7600 (which will automatically switch from cold ...
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0answers
16 views

Need to run a “C” wire to thermostat but control board has no “C” [duplicate]

I am looking to replace a thermostat with one that needs a C wire... which my current thermostat does not. I have some extra wires in the thermostat wiring that are unused... so I went down to the ...
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2answers
64 views

Honeywell home ventilation system with no c wire for thermostat. How can I substitute the g for the c without blowing a fuse?

I'm hoping to get some help with my thermostat problem. We bought our home brand new and it came with a very basic thermostat (non programmable and runs on batteries). I want to upgrade it to a wifi ...
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1answer
153 views

why does my heat pump wiring diagram show 7 wires going to the thermostat but the thermostat only says it needs 5?

Here is a link to the wiring diagram for my heat pump. The thermostat that I am planning on buying has the following terminals C, G, Y, O/B, RC, R, Aux, E, and L. The instructions say to jump the RC ...
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1answer
42 views

Zoned oil furnace and AC thermostat question

I recently moved into a new home and wanted to replace the old thermostats with digital Honeywell ones. From what I understand the home has a Rheem 10 Seer (1996) compressor and a Williams oil furnace ...
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3answers
75 views

A/c makes the lights turn on and off! No Joke!

The lights on the first floor, upstairs bathroom and upstairs Laundry room won't work. The breakers did NOT pop The air conditioning was running this morning but is not working now. When the ...
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1answer
196 views

Where can I connect the C wire on the A/C side?

I’m trying to replace my thermostat with the Honeywell Smart-WiFi thermostat. Quick summary, I have an extra yellow wire which I’m making the C wire, but its not connected at the other end and I’m not ...
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2answers
254 views

Can I install a Honeywell WIFI Thermostat?

I have done quite a bit of research and have not been able to find an answer I am looking for. I currently have a manual digital thermostat that is not programmable made by Braeburn. My system is a ...
2
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1answer
45 views

Is it a problem that I have two of each color wires on my Honeywell thermostat?

I am thinking about upgrading my Honeywell thermostat. Every thing I have seen describes / shows a single wire for each color. My current thermostat has two wires connected to each terminal (two green ...
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0answers
39 views

Thermostat replacement

My old thermostat is a carrier t-stat and has a jumper wire between o/w2* and L I am upgrading to a honeywell wifi t-stat, should I install the same jumper wire on the new thermostat? I have an ...
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0answers
13 views

Connect Taco Radiator system to a new Honeywell wireless thermostat

I have a Taco model 572 valve connected to an existing wired Honeywell TH8110 thermostat for my oil fueled radiator system. I'm getting a new Honeywell TH6320 wireless thermostat for a new A/C ...
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2answers
1k views

Line voltage thermostat to shut off attic fan when outside temp is close to inside?

I have an attic fan with a thermostat, but with the high heat these past weeks, the outdoor temperature is often above the thermostat setting. Thus, I'm just replacing all the air in the attic with ...
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2answers
1k views

How can I modify a 4 wire thermostat to a new thermostat requiring c wire?

I attempted to replace my thermostat with a fancy new Trane z-wave enabled model. To my dismay my home was only wired with a 4 wire setup with no 5 hidden in the bundle. I followed Insx on the web ...
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2answers
3k views

Adding a C wire to a new Honeywell WIfi Thermostat

I am trying to install a new Honeywell touchscreen WIFI thermostat (http://www.homedepot.com/p/Honeywell-Wi-Fi-Smart-Thermostat-RTH9580WF/203926327?N=5yc1vZc5kl) and need to add a C wire to my ...
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2answers
1k views

Can you terminate more than one common on the furnace C terminal?

TL;DR: Can you terminate more than one common on the furnace C terminal? Background: I've linked a diagram of how my non-programmable thermostat is currently hooked up. I want to replace it with a ...
11
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2answers
8k views

Why is my Nest thermostat not working with A/C?

I installed Nest thermostat a few weeks ago, replacing an old Lux programmable thermostat (there was nothing wrong with it). I connected 4 wires (R,W,Y and G) to the Nest. But as soon as I'd ...
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2answers
586 views

Wifi Thermostat wiring

Replacing 2 Hunter thermostats with a Honeywell RTH9580 Wifi. Neither unit has a C wire - I'm comfortable with the upstairs high efficiency unit, but the downstairs older unit has thrown me for a ...
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3answers
3k views

How can I use a separate transformer to provide a C wire to my thermostat?

I Purchased the Honeywell WiFi Prog Thermostat to replace my Round Digital Honeywell Thermostat. I have separate Heating and Cooling (Heating is a Weil McLain Boiler for Hot water baseboard and Hot ...
3
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2answers
525 views

Can I use an unused wire as a “C” wire?

I just bought a new thermostat that is Wi-Fi enabled and it requires connection to a "C" wire. The old thermostat does not have one running to it, but there are other unused wires. The thermostat ...
4
votes
2answers
626 views

Connection for C wire on Mastertrol Mark V zone control panel

I have spent hours searching the web for information on this 20+ year old zone control panel, which supports 3 zones of Heat and A/C. The thermostat I'm replacing (on Zone 3) connects to T4/T5/T6 as ...
2
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1answer
96 views

Can I insulate between a brick chimney and drywall?

Can I insulate the space between a brick chimney and the drywall inside my home? I am getting heat transfer from the brick to the drywall in the summer from the sun heating the brick. My thermostat ...
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4answers
2k views

HoneyWell Wifi Thermostat and C wire

I just bought the HoneyWell Wifi thermostat and so wanna use it. However my old Thermostat was battery powered and does not use the "C" wire. I opened up my panel and found that there were three ...
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1answer
42 views

air conditioning system stays on even when we turn off our thermostat

Our A/C system stays on even when we turn off our thermostat. What should we do to try to fix it?
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1answer
56 views

Is my thermostat transformer voltage too low?

I measured the voltage at the thermostat Rc to G and Rc to Y terminals, and they read 16.2V and 16.34V respectively. Shouldn't I be measuring 24V+/-? I purchased a Nest thermostat and it will not ...
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1answer
59 views

Which wire is the C wire?

Model: Goodman AWB30-08C Electric AC/Heat I'm hoping someone can help me identify the 24V C wire. Fortunately the thermostat line has a spare wire already run, so I just need to find the C wire in ...
2
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2answers
5k views

Are there any ductless mini split systems that offer standard HVAC wiring controls?

Have been looking for in the US a ductless mini split heat pump system something like the Mitsubishi Electric Mr. Slim that uses a non proprietary wiring scheme for its wall mounted thermostats. ...
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4answers
10k views

Why don't programmable thermostats automatically switch between “Cool” and “Heat”?

While I can set my house to be a particular temperature, I still have to manually switch it between "Heat" and "Cool" mode, and this seems to be true of every thermostat (programmable or not) that ...
3
votes
2answers
1k views

Trying to wire a 240v line-voltage thermostat

I am trying to replace my old 240v line-voltage thermostat with a modern version. The problem is that after wiring the new version in like the old it doesn't work. I have (2) 12-2 wires coming out of ...
0
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0answers
71 views

Master-Slave type Thermostat?

I have 4 thermostats located in four different zones and a separate AC thermostat. I want to get some programmable thermostats for each location. I could buy 4 individual programmable thermostats ...
0
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1answer
675 views

Need help running and connecting a 'C' wire to my new thermostat

I have a Laars gas boiler that has 3 heating zones; basement, 1st floor, and 2nd floor. I want to replace the old mercury honeywell tstats on the 1st and 2nd floor with newer honeywell RTH9580 wifi ...
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1answer
76 views

Can I change my standard thermostat to a Wifi one?

I have a (quite standard) TR-010X T6360A thermostat that looks like this: And this is the wiring diagram: Can I install the Heatmiser PRT-TS WiFi Touchscreen Programmable Thermostat? This is the ...
0
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1answer
845 views

Is it possible to use add-a-wire with my current configuration to add a C-Wire? [duplicate]

I only have four wires: Red, Blue, Yellow, and Green. My old thermostat jumps the R to RC and leaves C empty. I have a new thermostat that wants 5 wires, but I don't have C. I am not sure what the ...
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1answer
2k views

Wireless Thermostat C-Wire Substitute

I've read How can I add a "C" wire to my thermostat? and checked out the Venstar Add-A-Wire Accessory. I've watched Honeywell's YouTube video on "DIY Wi-Fi Thermostat Substitute G-Wire for C-Wire," ...
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1answer
526 views

How to wire a new Honeywell RTF6580WF thermostat to replace a Chronotherm IV?

I have an old Honeywell Chronotherm IV thermostat that I am trying to replace with a Honeywell RTF6580WF wifi thermostat. I have a gas furnace and an air conditioner. Wiring for Chronotherm IV ...
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0answers
46 views

Using a second thermostat to balance temperatures thru fan-only control

Like many others, temperatures between the two levels of my house are uneven. This is particularly noticeable as spring arrives and the upper floor (above ground) enjoys solar heating (so the heater ...
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2answers
112 views

Replacing old thermostat with new wi-fi Honeywell

I'm trying to replace my old mercury thermostat with Honeywell Rth8580wf. The cable has 8 wires, only 4 were being used. The wire colors and letters on the thermostat do not match up, so I'm left with ...
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1answer
44 views

How to install thermostat with plug in heater?

My house has three electric wall heaters in different rooms used to augment the gas forced air that heats the whole house. These electric heaters are mounted on the wall, but plug into standard 120v ...
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0answers
408 views

Please help establishing a C wire for new tstat

I bought a new WiFi tstat as a replacement. The tstat controls my second floor hot water baseboard heat and my central air conditioning. I've located all the wenter image description ...
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0answers
31 views

Can I use a transformer to power a thermostat? [duplicate]

So I bought a Nest Thermostat off amazon, I read they used batteries and what not and after I purchased it I was looking at the description on amazon and it said it was a built in rechargeable battery ...
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0answers
57 views

Why is my heat not shutting off at the set temperature?

When I turn the heat on on my central heat and air unit, the heat came on then continued to run getting really hot. It would not shut off unless I turned from auto to on then back. Sometimes I had to ...