Heat Pump Thermostat O, B, and C Terminal Variations Explained

Why Heat Pump O, B and C Thermostat terminals can be confusing. O/B? B/C? What does it all mean? Here's the answer....

[@chewyyo3383]

The way you broke down why O/B and O/C are combined was beautiful ✌🏿

[@riveraexal]

Perfect explanation video thank you so much!!!!!

[@artjavila12]

Dude. Best explanation. Appreciate this.

[@MechTechRW]

This exact video helped me figure out the problem with a new installation. Just installed using same thermostat but previous unit defaulted to cool. Big big thank you!

[@JerseyMikeHVAC]

Great to hear

[@wadebrink8149]

Thanks for the HP stat video. 😊 needed that

[@keepthinking2666]

I remember about 26 years ago when I got on the trade it was explained to me as rud ream and a few others that were manufactured down in the south never really made it up north for the most part and since it's much harder down there and they don't require the heat as much it defaults to cool and then you have to energize to bring on the heat vice versa north of the Mason Dixon line where you get severe winters you want to default into heat in case anything happens and energized to cool

[@JerseyMikeHVAC]

Back then I remember most people saying heat pumps are only a southern thing. Can't recall even seeing them until I headed south and worked in Florida for a few years. It was only about 5 years ago that I was convinced they could give off enough heat to be used up north. .

[@TMoS8713]

This is an awesome video thanks for your knowledge on wiring heat pump systems. We are beginning to get to a point where the WAP program wants these installed as much as possible where feasible, so all the extra advice is greatly appreciated!!

[@JerseyMikeHVAC]

Glad it was helpful!

[@houcineelmerzak3299]

Thank you for your effort.I will appreciate if you can give us a heads up on trane roof top schematic

[@1971omi]

Hi Mike, lots of tech I have seen my hvac feild, especially during heat mode they are clueless, I'm always fascinated by old school actual mechanical defrost and bunch of Relays do the defrost board. I barely come across the old heat pump that has these components, is there anyway you can put video on this one please. Thanks

[@l.crossjr]

Great content and examples

[@JerseyMikeHVAC]

Thank you

this is the best, yet. Thnx, Maybe, please, you could explain for me, what may be the cause s for a heat pump that is in the selected HEAT MODE, to NOT turn on the OUTDOOR UNT, but automatically turns on the INDOOR unit and allows it, to blow warm air in the apt. Is this how all Tstats work? They will automatically turn on the heat strips (as in my case here), if there is an issue with the first stage heat? Your reply (or any othe), will be appreciated. Thnx again.

[@JerseyMikeHVAC]

It could be a lot of different issues and requires a diagnostic process to weed it out, but I would start first with checking the breaker to see if it's tripped, and if so, why.

[@kens1955]

Can you use a jumper from any other source in the thermostat to power the OB valve.

[@JerseyMikeHVAC]

The R terminal.

[@Tara-Oziray]

I have old thermostat with wires in both o and b. Trying to connect to a nest but confused with separate wires for both b and o. Any help? Or I need to change the entire wiring system?

[@JerseyMikeHVAC]

What is the make and model of the thermostat? What brand heat pump system?

[@Tara-Oziray]

@JerseyMikeHVAC thank you for replying back. I have a old TrolAtemp chromotherm III thermostat with 6 wires and separate o and b wires attached to different slot.

[@deshacks]

Mine doesn't have o/b wire. How is operating? And how can I install a smart thermostat on that wiring

[@JerseyMikeHVAC]

What model unit and what kind of thermostat currently?

[@gotchaplumber]

So, if no 24v sent via orange wire, then would system be in heating mode? O=cooling. Are my thoughts correct, Mike?

[@JerseyMikeHVAC]

Yes, that's correct, unless it's a Rheem and a couple of other brands, where powering the B would activate heating mode and no power = cooling.

[@guygravel4804]

OK so I have a O and B wires from my old thermostat. Also I have a Internal switch that is set on the O. Can I then use Just the O wire to put on the new Thermostat re.O/B ? using the "ecobee smart Thermostat Premium

[@tonyelliott3446]

Ok my man I'm just a little stuck here.. I had a thremostat that had O and B .. O is orange .. B is blue .. went to put in a new Stat and my O B is together like u have in the video . I have a trane heat pump .. so in my Stat do I put B has my heating or O ?

[@tonyelliott3446]

Reason I'm asking this... don't seem my heat pump is working by its self . I only get good heat when aux heat is kicked in . And both my heat pump and strips are both working at the same time. When Aux heat is kicked in you can feel the line and feel the it is hot and heat pump is working. But wheb it kicks down to idle heat . My heat pump is not working . So .. do I set my Stat as B for heating ? To kick in the heating valve? Or O .. if Blue is either common or reverse valve on a trane . What do I set my Stat as ? O for heating or B for heating

[@JerseyMikeHVAC]

Trane powers their reversing valve for cooling mode and it defaults in heating mode unpowered, so you are going to use the orange on the O/B terminal and check the thermostat for a setting that asks which mode to power it in. You will select O (they usually come default in that setting but double check). Trane designates their common with a B terminal in their equipment, so blue will land on the C terminal in the new stat.

[@tonyelliott3446]

That's what I got .. just seems like the heat pump isn't working when I am in reg heat mode . But works fine when aux heat kicks in . I have a 2 stage heat 2 stage cool . When in idle heat my lines go cold . But seems to heat just fine in stage 2 when my strips and pump work together .. hope that makes since ..

[@JerseyMikeHVAC]

It's possible you may have a refrigerant issue. The hot line could just be refrigerant absorbing the heat off of the electric strips.

you are lucky still. My HEAT PUMP does not come on in the HEAT MODE at all. BUT, the indoor unit ONLY comes on and gives some heat, not a whole lot thought. I am hoping some one can reply to tell me what could be the cause why my out door unit will not come on when the thermostat is in the heat mode, but he indoor unit does, and blows heat from the heat strip,. Its weird.@@JerseyMikeHVAC