# Replacing a 120V fan coil thermostat. How to wire?



## Bitters (May 28, 2014)

Yes OK to 5 wires on the Neutral. There shouldn't be a neutral at the stat. I'm a little confused.


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## maxVa (Jul 27, 2015)

Thank you for responding. I am attaching the label with the wiring diagram.
Does it help?


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## beenthere (Oct 11, 2008)

Do you have a neutral coming to the thermostat? I believe your new stat needs a neutral to work.


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## maxVa (Jul 27, 2015)

yes, there is an "N" terminal on the new thermostat.


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## beenthere (Oct 11, 2008)

Is there an actual neutral wire at the thermostat.


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## maxVa (Jul 27, 2015)

No there are no wires at all, only terminals. I was going to go buy wires and put them in myself.


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## zappa (Nov 25, 2011)

maxVa said:


> No there are no wires at all, only terminals. I was going to go buy wires and put them in myself.


I think it would be best to take it back and get a thermostat that you can use with your existing wiring. You have a single speed fan so you won't be able to use that feature.

You don't have a neutral at the thermostat location and would have to replace the entire cable all the way back to the fan location with one that has a neutral wire. This could be easy or impossible without tearing the walls open as we don't know the fan and thermostat location.

But in the end, you will have something similar to your old thermostat with no fan speed control.


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## beenthere (Oct 11, 2008)

maxVa said:


> No there are no wires at all, only terminals. I was going to go buy wires and put them in myself.



I meant is there a neutral wire at your current thermostat.


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## maxVa (Jul 27, 2015)

This is 120 Vac line. Isn't "N" and "load" the same in this case?

My old thermostat was connected to just 2 wires coming out of the wall hotwire (black) and load (white).

Thermostat's "heat" (yellow wire) and "cool" (blue wire) terminals were connected to load wire.

Thermostat's "com" terminal is connected to black wire.

I am attaching the pix.

I think there is a way to wire it without adding any new wires. I definitely do not want to rewire my system, adding wires fromt he box to the fans, etc. I do know, however, that some of my neighbors installed new thermostats, similar to the one I'm installing. I'm pretty sure they did it without rewiring their system. (Alas, they moved out and I can't ask them how they did it....)

Also, I do not want to have three speeds. So, if it's possible to just ignore hi-med-low terminals, I'd gladly do that. I'm just concerned that in this case the chain would be broken. On the other hand, I'm concerned that if I just connect hi-med-low terminals to load, I'd short circuit the system.


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## zappa (Nov 25, 2011)

"N" is Neutral and at ground potential. It's at your fan location but probably not at your thermostat unless you see an unused white wire in there. I'm guessing that your new thermostat has some sort of electronics inside? That would be the only reason for the need of a neutral at the thermostat.

If there is a grounded metal box in the wall, that could be how your neighbors got the neutral. The ground is not supposed to be used as a neutral but it's often done and against code.


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## maxVa (Jul 27, 2015)

yes, the new thermostat is electronic.
http://www.grainger.com/ec/pdf/Dayton-Wall-Thermostats-1UHE3-1UHE4-OIPM.pdf

my box is grounded, but i wasn't going to connect to it. the thermostat's body is all plastic anyway.

Are you suggesting that I should connect N terminal to the ground?

Should I just connect "Heat" and 'Cool" terminals (##1 and 2 in the diagram above) to the white (load) wire?

Should I keep hi-med-low terminals (##5, 6, 7 int he diagram) disconnected?


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## zappa (Nov 25, 2011)

Neutral aside, if you were able to get this thermostat to work your only connections would be "L" and the other two wires on just one of the fan connections. Your pick on which one.


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## maxVa (Jul 27, 2015)

So it would be essentially the same as what I had with the old thermostat: Hotwire to "L", and "Heat" and "Cool" terminals (#1 and #2) both connected to "Load" (white) wire. 

The new thermostat switches cool/heat (open/close on rise).


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## zappa (Nov 25, 2011)

maxVa said:


> So it would be essentially the same as what I had with the old thermostat: Hotwire to "L", and "Heat" and "Cool" terminals (#1 and #2) both connected to "Load" (white) wire.
> 
> The new thermostat switches cool/heat (open/close on rise).


Close, the bottom black wire with the red wire nut goes to "L". The top white wire with the red wire nut goes to either 5, 6, or 7. Take your pick.

You can only turn both fans on at the same time because you don't have a third wire so you can't use 1 or 2. You could try tying them both together on 1 and 2 like your old thermostat but the new one is electronic and I don't know how it will react. Might work, might not.


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## zappa (Nov 25, 2011)

Looking at 1 and 2 again, they might not even switch with the thermostat set point, but remain on with the selection of cool/heat so your fans might run continuously if you tried using 1 and 2. This is a good question for member *beenthere *or maybe someone else might know.

Also, looking at the fan current specification on the new stat, it's 1 amp in heat and 3 amps in cool. I don't know how it could be different but that's what it sez. So running 2.6 amps worth of fans in heat mode is higher than the spec. But maybe it will be OK since no amps are being drawn on 1 and 2 which are rated for 9 amps heat and 6 amps cool.

http://www.grainger.com/ec/pdf/Dayton-Wall-Thermostats-1UHE3-1UHE4-OIPM.pdf


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## maxVa (Jul 27, 2015)

If I connect only to 5,6, or 7, the device will definitely NOT work as a thermostat. 

Since HEAT and COOL are on terminals #1 and 2, they definitely should be in play. That I am positive about.

Btw, my both fans are in series, so I always turn them on and off together. For the purposes of wiring, consider it a single fan.

I'm not interested in having variable speed (hi-med-lo) per se--it has no practical application. The only reason why I am thinking about it, is I need to make sure that the circuit is complete. 

Not using speed terminals ##5-7 would break the circuit only if speed selector is in series with the thermostat circuit. When I look at the wiring chart again, it seems to me that they cannot possibly be in series. So, I'm leaning towards not using ##5-7 at all. If I don't use it, I believe it should be equivalent to having always-on "high" speed (all current goes through terminals #1 or #2, depending on which circuit is open).


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## maxVa (Jul 27, 2015)

I think that in my case, the fan actually takes the spot of either cooling or heating element in the wiring diagram. So relevant amps are the ones for heat and cool. Heat circuit is 9 amp and cooling circuit is 6 amp, both well above 2.6 amp.

With the info int he manual it's hard to understand what each circuit is doing and how are they connected to each other. It's a "black box." That's why, I'm here, I guess.


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## zappa (Nov 25, 2011)

You will have to wait for someone else who knows what those symbols are on 1 and 2. They look like water circulation pumps to me and you don't need to control them in your situation.

Your fans are wired parallel, they would be very slow if wired in series. They are also not capable of different speeds even with the new thermostat. That is only a selector switch for different motor windings, not a built-in speed control.


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## zappa (Nov 25, 2011)

If they are circulator motors you should be OK to use 1 and 2 tied together just like your old thermostat. It won't burn anything up to try it like that.


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## maxVa (Jul 27, 2015)

Yes, you're right the fans are parallel, but what I emant to say that they are controlled together by one thermostat: either both are on or both are off.

Yes, I'm leaning to just tying together terminals 1 and 2 to load and connecting black wire to L terminal. In all likelihood this should be similar to the old thermostat setup.


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## zappa (Nov 25, 2011)

At first I though they might be water valves and may stay open all of the time. After making the image bigger they look like circulators and it wouldn't make any sense for them to be running constantly. The N.C must mean controlled by set point and not the heat/cool switch. But I would also think the fan should shut off at set point as well or it would be blowing hot and cold air when the circulators are not running.


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## beenthere (Oct 11, 2008)

Without a neutral. The new stat won't know what temp it is, so it won't turn on the heat of cooling. Its not a mechanical stat.


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## maxVa (Jul 27, 2015)

Qiute possibly. I tried various options with an ohmmeter. The cooling circuit is open, when I select cool, but it does not respond when change the setpoint. 

Neither could I make heating circuit open. When I switch to heat, cooling circuit breaks, but heating does not open.

Granted the voltage of a tester was way below the required *)-120Vac. And I assume ohmmeter uses DC.


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## supers05 (May 23, 2015)

TLDR all of this thread, but what I did read is it should would by using terminals either 5,6,7 or tying them together to the fan. 

Terminals 1,2 are for a valve. Some times you'll have a second coil and loop. (one for heating and one for cooling) You don't have it and it's very rare due to the cost involved. More commonly you will have supplemental heat, through a relay. Both these cases require a separate terminal for heat and cool. For your case, ignore it completely. (it's only rated at 1A anyways. Too low for the fan) 

The fan terminals are controlled by the fan selector switch/option. 
Auto=on only when needed to cool/heat (this is what you need to use) 
On=always on (you don't want this) 
Speed setting = ignore this. Set it to the whatever you connected the fan to and forget it. 


Cheers!


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## beenthere (Oct 11, 2008)

supers05 said:


> TLDR all of this thread, but what I did read is it should would by using terminals either 5,6,7 or tying them together to the fan.
> 
> Terminals 1,2 are for a valve. Some times you'll have a second coil and loop. (one for heating and one for cooling) You don't have it and it's very rare due to the cost involved. More commonly you will have supplemental heat, through a relay. Both these cases require a separate terminal for heat and cool. For your case, ignore it completely. (it's only rated at 1A anyways. Too low for the fan)
> 
> ...



The new thermostat is a 120 volt voltage digital. It needs a neutral to work.


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## zappa (Nov 25, 2011)

supers05 said:


> Cheers!


Yeah, the OP doesn't have a neutral but thanks for clearing up the purpose of terminals 1 and 2. Your super! 




> Also, looking at the fan current specification on the new stat, it's 1 amp in heat and 3 amps in cool.


I took this to mean the fan circuit/switches, not terminals 1 and 2. But why would they rate them differently?


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## supers05 (May 23, 2015)

Looking back now, i dunno what i was smoking, but i dunno why i mentioned the rating difference, lol. 

Anyways it's common for the valve terminals to have different current ratings then the fan. 

Cheaper/smaller contacts on the relays. Or they even might be using something solid state like a triac, etc. If they can save a penny, they will. 

I figured that you guys understood the neutral part, so I didn't mention it. Too bad it can't steel power through the blower. (microsecond pulses) It's not like it needs a whole lot. 

We use the tried and true old school Honeywell thermostats. T6069 (a, c, or d) if i recall the number of the top of my head. Something like below. They'll take a beating and keep working. Had to change one today that the contacts were welded shut. (aquastat arced to the pipe blowing a hole through it and the pipe) 

http://www.alpinehomeair.com/viewproduct.cfm?productID=453069320

Cheers!


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## zappa (Nov 25, 2011)

zappa said:


> Also, looking at the fan current specification on the new stat, it's 1 amp in heat and 3 amps in cool.





supers05 said:


> Looking back now, i dunno what i was smoking, but i dunno why i mentioned the rating difference, lol.
> 
> Anyways it's common for the valve terminals to have different current ratings then the fan.


Sorry for the confusion super, that was my quote from another post. Could you take a look at the specs on the first page of this PDF please.

http://www.grainger.com/ec/pdf/Dayt...?cm_mmc=PJX-_-GraingerBrand-_-43737-_-Generic

Heat / Fan
9A / 1A

Cool / Fan
6A / 3A

This seems like the fan contacts are rated for 1 and 3 amps. If so, how could they be different if they are using the same contacts? Do you think it could be a typo and they meant to say 9 and 6 amps for the fan? If terminals 1 and 2 are valves they certainly wouldn't draw more than a fan would they??


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## supers05 (May 23, 2015)

I know on the old style the power actually passes through the switches on the front. You can see the contract arc when it's dark. The different switch positions can have different ratings. Maybe they are doing the same here. I do see on the pdf, it mentioning the slide contacts. Maybe the digital part is only for temp control, and just controlling the modulation though a single relay, with the heat/cool and fan selector passing power. 

Some building setups can be different. Like using resistive heating for the shoulder seasons. Or in the south during the cold periods. It wouldn't be much heat. I think the cooling rating is just A byproduct of that, but i suppose it's possible that some engineer out there could think of something silly to use it for. 

Cheers!


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