# Thermostat with separate O and B terminals



## David2build (Jul 9, 2018)

I am trying to install a new thermostat and it seems like most new thermostats have a combined O/B terminal. I bought a new one with the following terminals:
O/B Y B G W/AUX. but mine is RC RH (jumper on these two) B O Y W (Nothing connected to W)G C.

I have a brand new A/C unit and I am being told that because I have separate O and B terminals, most new thermostats won't work. Nest and Ecobee both told me it wouldn't work. Can anyone help me?


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## John Smith_inFL (Jun 15, 2018)

there should be a toll free number on the box to call if you need assistance
in installation. mine also has a paper label on the back of the T/S itself
with the phone number. . . . . I would do that.


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## David2build (Jul 9, 2018)

So I think that the person who installed my unit put a wire in the wrong spot or something.

This is a link to my air conditioner. I have the PHJA-048: 
http://dms.hvacpartners.com/docs/1011/Public/05/42701150302.pdf

On page 18, it shows where the 24 volt connections should go. From what I'm seeing, it should have been connected to just the O portion of the terminal and I think that the blue wire should go to the O and the white to W. But I'm no HVAC tech. Just looking for some advice.

This is the link to the current Thermostat that I have:

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/1000%20Series%20Manual.pdf

This is exactly my setup:
RC - Jumper with Red Wire
RH - Jumper with Red Wire
B - Blue Wire
O - White Wire
Y - Yellow Wire
W - No Wire
G - Green Wire
C - Brown Wire

:vs_whistle:


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## CaptTom (Dec 31, 2017)

First things first. Disregard the color guide. Connect to the the terminals based on their labels.

I don't see any reference to "B" in the diagrams on either page 14 or 18 of your air conditioner manual. Admittedly, I didn't read the whole thing. Does it mention B somewhere else?

O and B control the heat pump reversing valve. B is energized to turn heating on, O is energized in cooling. If I understand this correctly, you should have one or the other, not both. Newer smart thermostats probably have a configuration setting for that. So it can use the same terminal for O or B ("O/B".)

I'm no expert, just a DIY'er who has had the opportunity to wade in a little too deeply into this thermostat wiring thing.


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## BayouRunner (Feb 5, 2016)

Just because all the wires are hooked up on the thermostat doesn’t mean they are hooked up on the other end of condenser or air handler. I doubt that both the o and b have to be hooked up to run your system


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## David2build (Jul 9, 2018)

Can anyone tell me what panel to open up to look at where the wires are supposed to be connected. Its on the roof and the last time I opened it up, I couldn't find where it was. Is it actually on the air conditioner itself? I would assume... Let me know if you think I should take a picture of the unit. Thank you!!!


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## BayouRunner (Feb 5, 2016)

Most likely the panel where your electric is going into it. Turn off power beforehand. Post a picture of your low voltage wiring and your wiring diagram will help. The wiring diagram is most likely on the inside of that panel that you take off. 


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## David2build (Jul 9, 2018)

Alright, went on the roof and opened up the AC unit. Now the low voltage Thermostat wires aren't directly connected to a terminal, they are spliced with larger wires that are then connected to a panel.

What's weird (Maybe this is normal) is that the Brown wire and the Blue wire are cut, yet both of those wires are connected to my existing Thermostat.

Her is what I see in the AC unit.
Brown and Blue - Cut off
White - Connected to Orange wire that runs to code "O"
Green - Connected to Green Wire that connects with another green wire to a blue wire that goes up to some transformer of some kind
Yellow - Connected to a Yellow wire that goes to code "Y"
Red - Connected to a bigger red wire that goes off and splits to multiple wires

Is this normal. How would I then hook this all up to a Thermostat with the following:

O/B Y R G W/AUX

Thanks!:vs_cool:

EXTRA CREDIT: Can anyone tell me why this black wire is disconnected, it has a connector on the end, you can see it in the pictures. I didn't want to just connect it to something but I was just curious.

Thanks!


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## CaptTom (Dec 31, 2017)

OK, you found at least most of the labels, so you can now begin to follow wires.

O controls your heat pump reversing valve, and is energized for cooling.
R is power, should be connected to both Rc and Rh on the thermostat with a jumper.
W2 is second-stage heating, that doesn't seem to go to the thermostat anyway.
Y is cooling
C is the elusive "other side" of R, needed to power the thermostat.

Not shown is where "G" (the green wire, conveniently) is terminated, but if the fan works, we can assume it's OK.

It looks like C is connected to a brown wire. That's the one you want to connect to the cut-off brown wire leading to the thermostat.

Here's where I'm not sure. If the white and brown wires in the 4th and 5th picture are the same as the ones in the 1st picture, then obviously that's something internal to the unit, controlling the heat. Presumably you could just twist the brown "C" thermostat wire in there. But I'm only guessing, maybe a real HVAC expert will chime in here. If not, check for +/- 24VAC between that and the red wires, with the power on but no heating or cooling. That would prove my theory, and that it's safe to connect that way.

Blue is supposed to be "Y2," second-stage cooling. If you don't have a 2-stage system, that one can be left unconnected.

Everything else looks like it's correct. There's no orange wire in the thermostat cable, so connect white to "O" at the thermostat. Feel free to stick labels on the wires so the next time you or someone else has to go through this, they don't have to climb up on the roof!


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## David2build (Jul 9, 2018)

It worked. Thanks all. Do you know how I would be able to figure out if I have a second stage system or not? 

Do we know why that black wire with the connector on it in the second to last picture is disconnected? Should I just leave it?


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## CaptTom (Dec 31, 2017)

David2build said:


> It worked. Thanks all. Do you know how I would be able to figure out if I have a second stage system or not?
> 
> Do we know why that black wire with the connector on it in the second to last picture is disconnected? Should I just leave it?


Great! Glad it's going.

1) Offhand, I'd say if W2 was connected before, it has a second-stage heater. But I'm not really familiar with those, we don't use them much in our climate.

2) See page 17 of the manual: "Blower speed tap can be changed by replacing the factory installed blue low speed tap wire (cooling) with the unused black high speed wire in unit control box. The red medium speed wire is factory installed to operate with a call for supplemental electric heat." (The hint was the green wire; it's typical to be able to set different fan speeds when installing these.)


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