Auxiliary heat low temperature setting

[Johnnycombo]

I have a Carrier 38MURAQ30AB3 high heat pump, the specs say it works to -22°F (just installed last week).

The Nest auxiliary low temperature is set to 0°F, any suggestions to operate at lower temperatures?

[ivanrussell · Accepted solution]

Can you post a picture of your thermostat wiring? I have the same heat pump with a 40MUAA sure handler and I'm pretty it's set for double stage. It's been working, was 16f last night. It's been installed for about a month and I'm wondering what the low end performance is like. I have the aux heat breaker off. 

[Johnnycombo]

 This is a screenshot of my wiring. The installer set the dip switches for the heat pump and air handler to control the stages of operation, but they also set the auxiliary heat low temperature on the Nest.

[Johnnycombo]

 This is the thermostat wiring at the air handler, the 2 conductor wire goes to the humidifier.

[zoeuvre]

Hi folks, 

Thanks for chiming in, @ivanrussell. 

@Johnnycombo, uh-oh! Thanks for posting. The Carrier 38MURAQ30AB3 high heat pump is rated to operate down to -22°F, which is quite impressive. Are you located in North America or Europe? What type of Nest Thermostat do you have? Also, could you send us a photo of your previous thermostat wiring configuration se we can take a closer look? 

I'll look forward to your response. 

Best,

Zoe

[Johnnycombo]

I live in south western Pennsylvania,USA close to Pittsburgh.  I’ve had my nest learning thermostat 3rd generation for about 4 years now and decided to keep it with my new heat pump system. 
    At times it does go below zero degrees Fahrenheit in my area and would not want to be paying for auxiliary heat when my heat pump can handle the lower temperatures. The thermostat works fine with my new system, I would just like to see the auxiliary heat lock out temperature go low enough to accommodate the new heat pump technology! 

[Johnnycombo]

I see that the auxiliary heat lock out setting has changed! Software 6.2-27

    The low temperature is now +10°F with the added choice of "Never use ault.". That's better than turning off the breakers. I just watched a YouTube video about the new cold climate heat pumps, one of the experts from Maine, USA, claims that most new installations aren't even adding auxiliary heat systems and rely on the heat pump only.

[zoeuvre]

Hi Johnnycombo, 

I'm sorry for the delayed response. It's great to hear that you are utilizing your Nest Learning Thermostat with your new heat pump system. To adjust the auxiliary heat lockout temperature and potentially rely on your heat pump only, you can follow these steps:

1. Open the Nest app or go to the thermostat's settings directly on the device itself.
2. Look for the setting related to auxiliary heat or emergency heat lockout. In your case, with software version 6.2-27, it appears that the low temperature limit is +10°F.
3. If you want to enable the heat pump to handle lower temperatures without auxiliary heat, you can select the "Never use alt" option. This will prevent the thermostat from activating auxiliary heat regardless of the temperature.
4. After adjusting the auxiliary heat lockout setting to your desired preference, save the changes and exit the settings menu.

It's important to note that relying solely on the heat pump without auxiliary heat in extremely cold temperatures may result in reduced heating capacity and potentially longer heating cycles. Depending on the specific conditions and capabilities of your heat pump system, it's advisable to monitor its performance during extreme cold snaps to ensure adequate heating.

Let us know how it goes.

Regards,

Zoe