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

[ielazarb]

@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.

[ielazarb]

@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

[Markjosephp]

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

[ielazarb]

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

Bosco

[ielazarb]

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

Thanks

Bosco

[ielazarb]

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

[CoolingWizard]

@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

[ielazarb]

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.

[ielazarb]

 

[ielazarb]

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?

[pereztzum]

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.

[ielazarb]

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.

[CoolingWizard]

@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

[ielazarb]

@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.

[CoolingWizard]

@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 

[ielazarb]

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.

[CoolingWizard]

@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

AC Cooling Wizard

[ielazarb]

 

@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.

 

 

 

 

 

[ielazarb]

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.

[CoolingWizard]

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

[ielazarb]

You mean these ones and just from zone one or both the zones?

 

[ielazarb]

@CoolingWizard 
And if there was a problem with my two zone controller then how is the existing Honeywell tstat working without any issues? At this time I am skeptical to experiment with my existing HVAC or controller. I think best to get a technician to connect the orange OB wires correctly in the two zone controller and then connect the orange wire in the Nest OB slot.

[CoolingWizard · Accepted solution]

@ielazarb , there has to be some kind of a configuration error.  Note the picture you provided and the notes I added on the upper right; the HVAC equipment connections. Note that bottom port is for EH, W2, and OB. Again, you have no wire connecting the to this port. So me your heat comes on and you get hit, you have to have gas furnace.  Try this, when the Nest Learning Thermostat display is blue, it is in cooling mode. When it is Orange it is in heating mode.  Your display was in cooling mode. So, if you think the Nest is initiating heat, just swap the White wire and the yellow wire. Then turn on cooling and see if anything changes. 

AC Cooling Wizard

[ielazarb]

@CoolingWizard I am all for experimenting but I am afraid I might damage the HVAC equipment with all this experimenting?

[CoolingWizard]

@ielazarb , we will not be damaging the system. We are taking steps to try to isolate where the heat signal is being generated from.  You put your Nest Thermostat on Cooling, and the Gas Heater comes on instead. We need to figure out why that is happen. So if we swith the W1 and Y1 wires we can see if it is the Nest thermostat causing this. 

AC Cooling Wizard