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Nest Thermostat Blowing Hot Air On Cool [Easy Fix]

Last updated: May 24, 2023

If you are dealing with a Nest thermostat blowing hot air on cool then this is the right guide for you.

Generally, if your nest is blowing hot air on a cool setting, this could be due to your thermostat setting, or you have a conventional heating system.  Another issue that can cause this problem is an incorrect heat pump orientation settings (O/B) settings.

Let’s look at the following table which summarizes the possible causes for a nest not cooling.

Read alsoo: Nest thermostat blowing cold air on heat

5 Possible reasons a Nest thermostat is blowing hot air on cool

Possible causeMain Fix
Thermostat settingsEndure you thermostat is in cooling mode (snowflake symbol)
You have conventional heatingGet an alternative cooling system
Stuck reversing valveReplace solenoid or reverse valve
Wrong Nest orientation (O/B) settingsCorrectly set the (O/B)
Wrong thermostat wiringEnsure your thermostat is properly wired.

Lets now get into the details of the troubleshooting, 

Thermostat settings

When you notice your Nest blowing hot air on cool, the first you might want to check is  the thermostat settings. While this is no brainer, many times it turns out that the whole cause of the problem is just a thermostat that is actually not set to cooling.

Solution

 Ensure that there is a snowflake symbol on the thermostat ( the snowflake symbol means the thermostat is set to cooling mode.

You have conventional Heating system

The truth is, if you don’t have heat but conventional heating (furnace) then you are going to have cooling. 

And it can be really challenging to tell whether you have a heat pump or a furnace for many homeowners especially if you have just moved into a new home. But here is the trick you can use

Check the label  or the sticker on the unit  or if you can’t find it look up the model number of your system on the internet.

Another way to tell whether you have a heat pump or not is by checking the  wiring of your thermostat. Typically for a heat pump system you are going to have a wire connected to the O/b terminal. If you don’t have a wire here you probably have  conventional heating.

Read also: Nest Thermostat Not Blowing Cold Air [Easy Fixes]

When you have  heat  pump systems and when you turn on heating, your outdoor unit should typically kick in.

If you believe you have a heat pump run a diagnostic test by following these steps:

  1. Set your thermostat to cool mode ( snowflake symbol should display)
  2. Set the temperature to something lower than the current room temperature
  3. Wait for a feel minutes and feel the air that comes out of the vents, it is cool, if now you might want to check the O/B wire settings

Also read: Nest not blowing cold air

Wrong Nest Heat Pump Orientation (O/B) settings

Now here is the thing, if your nest is blowing hot air on cool and blowing cool air on heat, you may have misconfigured O/B wire setting on your thermostat. O/B settings control the reversing valve.

Solution

To solve this problem you will need to reverse  the O/B wire settings either on the thermostat or App.

If you are using Nest Learning Thermostat and Thermostat E, follow these steps:

  1.  On your thermostat, go to Settings Nest settings icon.
  2. Select Equipment.
  3. Select Continue and then Continue.
  4. Select Heat Pump.
  5. The Nest Thermostat defaults to an O setting for heat pumps. 
  6. If the O option is highlighted, select B.
  7. If the B option is highlighted, select O.
  8. To make sure the issue is resolved, test your heating and cooling again.

If you are using  a Nest Thermostat  follow these steps

  1. Open the Home app Google Home app.
  2. Tap your thermostat.
  3. At the top right, tap Settings .
  4. Select Thermostat.
  5. Scroll until you find Heat pump. It should show which wire configuration is currently selected.
  6. If the O option is highlighted, select B.
  7. If the B option is highlighted, select O.
  8. To make sure the issue is resolved, test your heating and cooling again.

Read also: Nest thermostat wiring for heat pump

Stuck reversing valve 

Even when you have a heat pump, sometimes you may have it blowing hot air on the cool setting. This could be due to a stuck reversing valve. 

A reversing valve helps to reverse the direction of the refrigerant so that the heat pump can work both as an air  conditioner and a heating system.

The reversing valve can become defective over time in one direction (either in the cooling or the heating position) when this happens, that can cause the heat pump to either heat only or cool only.

Usually, when the reversing valve is defective, it is mostly its coli solenoid that is either cut or burnt. 

Solution

To solve this problem you need to replace the solenoid coil, but this has to be tested with a multimeter to verify its the cause of the problem. Otherwise if it’s the entire reverser valve that has gone bad, you will need a replacement. To fix this problem.

Read also: Nest Thermostat Keeps Changing Temperature

Wrong thermostat wiring

Wrong thermostat wiring could also be the reason your nest won’t cool. Your nest thermostat wiring should match the type of system you have.

 For example, if you have a single stage heat pump, your wiring will differ from that of a 2nd stage heat pump. Here are some wiring diagrams for different types of heat pumps systems.

1st stage heat pump

LabelFunction
Y1Compressor relay stage 1
GFan Relay
O/BHeat pump changeover valve
Rc24VAC power from cooling transformer
CCommon wire

2nd stage heat pump

LabelFunction
Y1Compressor relay stage 1
Y2 Compressor relay stage 2
GFan Relay
O/BHeat pump changeover valve
Rc24VAC power from cooling transformer
CCommon wire

Final thoughts

Well we hope that by now you have found a solution to a Nest thermostat that is blowing hot air in cool mode. Otherwise, if you are still facing the same problem we would advise that  you perhaps call a local expert to help with the troubleshooting.

Read also: New honeywell thermostat blowing hot air on cool setting

More resources: https://www.carrier.com/residential/en/us/products/air-conditioners/air-conditioner-service/air-conditioner-not-cooling/

Read also: White Rodgers Thermostat Blinking Snowflake [Solved]

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