topic Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump in Nest Thermostats

Nest Reverse Heating and Cooling - No O/B Wire for heat pump

ielazarb — Mon, 29 Jan 2024 02:35:38 GMT

@Patrick_Caezza I followed your post and advise for heating/cooling issue with my Nest 3rd gen learning thermostat. Since I don’t have a O/B wire, I put the white W1 wire into the O/B wire, reset to factory settings, set it up again (tried with both O and B as heat pump) but the heating and cooling does not work. In fact the thermostat is unable to control the unit at all. It just goes on heating if I leave it at B and just goes on cooling if I leave it at O setting in the Nest device. Any advise for me please?

Bosco.

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

ielazarb — Sun, 04 Feb 2024 20:36:22 GMT

@Patrick_Caezza not sure if you had a chance to look at my question but I am still having issues with heating and cooling with my Nest. Attaching a pic of my current thermostat. As you can see the orange wire is not currently connected at all and the same is true for my dual zone system panel. Hence on the Nest I am not connecting the orange wire at all. I have tried the white wire in W1, W2 (AUX) and OB. For each iteration, I reset to factory setting and setup the Nest. But with White wire in W1 the system cools instead of heating, with White wire in W2 (AUX) the NEST says Wiring incorrect and with White wire in OB the system just keeps heating. Any help is appreciated.

Thanks

Bosco

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

Markjosephp — Thu, 22 Feb 2024 19:41:18 GMT

Hello Bosco,

I'm sorry for the late reply, and I appreciate you reaching out with the details of the challenges you're facing with your Nest Thermostat. It sounds like you've been proactive in troubleshooting, but it's unfortunate that the issue persists. I'd be happy to take a look at this for you.

The Nest Thermostat typically requires the O/B wire to determine whether your system is configured for heating or cooling. Since you don't have a dedicated O/B wire, you've used the white W1 wire in its place. However, it seems that the system is not responding correctly to this configuration. Considering the challenges you've encountered with different wire placements (W1, W2, and OB), it might be worth verifying the compatibility of your HVAC system with the Nest Thermostat. Additionally, tell us the make and model of your HVAC system so we can check for additional information, and to confirm, is this a heat pump?

I'll look forward to your response.

Best regards,
Mark

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

ielazarb — Sat, 24 Feb 2024 03:52:55 GMT

Thank you Mark. It’s a Carrier brand Oct 2014 model# CA16MA036-A (CA16MA0360GBABA)
Regards

Bosco

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

ielazarb — Fri, 22 Mar 2024 20:44:25 GMT

Hello Mark just following up if you had a chance to look at my response

Thanks

Bosco

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

ielazarb — Fri, 22 Mar 2024 20:55:46 GMT

Tagging @CoolingWizard on this thread as I have seen some detailed and genius responses from Cooling Wizard. Any insight is appreciated Cooling Wizard.

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

CoolingWizard — Fri, 22 Mar 2024 22:49:43 GMT

@ielazarb , hello, your old thermostat appears to be a simple conventional system. Your system

is not a heat pump. You have a single stage, 3-ton air conditioner. In fact your system is an high efficiency system; 16 SEER. I hope you remembered to turn the power off before changing wires from your old thermostat to your new Nest thermostat. If you did not you might have accidentally created a short that would’ve blown the fuse in your air handler. If you have heating you likely have a gas furnace. Your wires are definitely as follows:

RC red wire, this is 24VAC Power In

Y or Y1 yellow wire, this is the compressor relay control

C blue wire, 24 VAC Power Common

W1 white wire, Heating Control Relay

G green wire, Blower Fan Relay

The operation of a thermostat is pretty simple in fact. The power coming to the HAVC transformer arrives on the R terminal. The thermostat then connects that incoming power to one of the control wires depending on the setting. If your set to Cooling, and the thermostat determines it needs to call for cooling it connects the power to Y and G. This will turn on the Blower Fan and the outdoor condenser unit. After a few minutes you will feel the cold air. As for heating, say a gas furnace. The thermostat connects the incoming power to the W wire. This signals the Integrated Furnace Control board to start the heating cycle. With a gas furnace the blower fan is under the control IFC and thermostat does not have to send power down the G.

Set up your nest as Gas Heat.
AC Cooling Wizard

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

ielazarb — Fri, 22 Mar 2024 23:28:28 GMT

Thank you @CoolingWizard so it means I don’t have to worry about O/B wire at all for the Nest? Just do the Rh, Y1, G, W1, C? How do I check the fuse for the air handler? I checked the fuse on the dual system zone controller and it’s not blown.

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

ielazarb — Fri, 22 Mar 2024 23:29:50 GMT

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

ielazarb — Fri, 22 Mar 2024 23:46:42 GMT

And just to mention when I connect my old Tstat back the HVAC unit works without any issues. If the fuse was blown won’t it have an issue with the old tstat as well?

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

pereztzum — Fri, 29 Mar 2024 00:26:33 GMT

Hello @ielazarb

I'm really sorry that you are having this type of issue with your Nest Learning Thermostat 3rd gen. We'll need additional information from you that would be best shared privately. I’m sharing a link to a form for you to fill out so we can look into this further. This form is only meant for you to use, so let me know once you’re done.

All the best,

Brandon.

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

CoolingWizard — Fri, 29 Mar 2024 00:36:12 GMT

@ielazarb , if you note the thermostats connect pn the upper left side. Both use a blue wire on Power Common C, red wire on R, Yellow wire on Y, Green wire on G and a white wire on W. There is no OB wire.

AC Cooling Wizard

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

ielazarb — Fri, 29 Mar 2024 00:44:19 GMT

@CoolingWizard and that is the question as to which wire goes into the Nest OB slot if I don’t have OB wire connected in my current Honeywell thermostat and controller? I have tried no wire in OB, the white wire in OB but it has not helped.

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

CoolingWizard — Fri, 29 Mar 2024 03:53:27 GMT

@ielazarb , the OB is only required for heat pumps. You do not have a heat pump. Hook your White wire to W or W1.

AC Cooling Wizard

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

ielazarb — Fri, 29 Mar 2024 04:01:24 GMT

Hello @CoolingWizard I tried both W1 and W2 (AUX) in the NEST but with W2 (AUX) I get a wiring error on NEST and with W1 it just kept cooling, the heating never comes on.

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

ielazarb — Fri, 29 Mar 2024 04:21:29 GMT

Hello @pereztzum I completed the form and chatted with Judy Lynn from real time support. Judy confirms that to use the NEST 3rd GEN on a HVAC system with heat pump, the OB wire is required and there is no workaround. I must get a AC technician to get the OB wire connected in the control panel and then only I can use the NEST 3rd GEN with the orange wire in the OB slot of NEST.

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

CoolingWizard — Fri, 29 Mar 2024 15:34:54 GMT

@ielazarb , the W2 is for stage 2 heating, or if there is a heat pump, this would be Auxiliary Heat. You cannot have a W2 is there is no wire in W1. Set your Nest Learning Thermostat up as Gas Heating, forced air. And put the white wire in W1. If you previously set the Nest up as a Heat Pump, you will need to go to Settings > Equipment and change it to Heat Fuel=gas, Forced Air,

AC Cooling Wizard

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

ielazarb — Fri, 29 Mar 2024 23:05:09 GMT

@CoolingWizard tried your suggestion (even reset to factory settings and set it all over again) but it keeps heating even if I set it to cool.

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

ielazarb — Fri, 29 Mar 2024 23:08:34 GMT

Perhaps the person from Google support chat is right that since I have heating and cooling in one equipment then it is heat pump. The original installer must have made some changes to not connect the OB wire at the controller in order to make the Honeywell thermostat work. So now I will have to get a HVAC technician to first connect the orange OB wire to the zone control panel. Then try the Nest with orange wire in the OB slot.

Re: Nest Reverse Heating and Cooling - No O/B Wire for heat pump

CoolingWizard — Fri, 29 Mar 2024 23:10:08 GMT

There might be a problem with your zone controller. Go to your zone controller and remove the white wires on the upper left side. See if your heat still comes on.

AC Cooling Wizard