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Why Your Nest Thermostat Keeps Turning the AC ON/OFF

Nest Thermostat Turning AC on and off

Why does the Nest thermostat keep turning the AC ON and OFF?

The Nest thermostat keeps turning the AC ON and OFF because it may have a faulty or missing C wire, the thermostat may have been placed incorrectly, the batteries may be low, or it could be a reset problem.

  • Faulty C Wire
  • Incorrect Placement
  • Low battery levels
  • Thermostat has disconnected from WIFI


Faulty or missing C wire

Sometimes the C wire in your thermostat may be defective. In this case, replacing it should solve the problem. If the wire is missing, you must consider getting one fitted properly.


Improper placement

Placing the thermostat in an inappropriate location can cause this problem. For example, if it’s near an air vent, the cool air makes the thermostat register the room as already cool. Similarly, if it’s near a window, the thermostat will register the room as warm. So, you must ideally consider keeping it away from air vents or away from a window.

Sometimes, the thermostat may be defective and would need replacement.


Low batteries

One indication that the batteries of the thermostat are running low is that the thermostat screen is faded or is blank. In such cases, replace the batteries.


Reset problem

This tends to happen when the Nest thermostat gets disconnected from the Wi-Fi. You will need to do a full reset to fix the issue.


Why does the Nest thermostat keep turning the AC ON?

The Nest thermostat keeps turning the AC ON if it is shorted, if the temperature setting is incorrect, the unit is defective, or if the wiring hasn’t been done properly.

  • Thermostat is shorted
  • Incorrect temperature setting
  • Defective unit
  • Improper wiring


Thermostat is shorted

You can check this by using a multimeter and testing the thermostat for continuity. If you notice continuity, it indicates a short connection. In this case, you must get the thermostat replaced.


Incorrect temperature setting

The temperature difference between the outside and where you have your air conditioner installed could be too high. For example, if the outside temperature is 95 degrees and the temperature where the air conditioner is installed is 65 degrees, the thermostat will be forced to keep the air conditioner running all the time to keep up to the temperature. Try a more reasonable thermostat temperature setting.


Defective unit

Although thermostats rarely run into problems, they can malfunction at times. To check if your Nest thermostat is working fine, keep a thermometer near it for a couple of hours and observe the reading. If the temperature is close to the home temperature, there are chances that the thermostat is defective. You can try getting it repaired or have it changed.


Improper wiring

Check if the wiring of the thermostat has been done correctly. Sometimes, the wires don’t match the colors. Have them changed.


Why does the Nest thermostat keep turning the AC OFF?

The Nest thermostat keeps turning the AC OFF because the Home/Away Assist setting isn’t enabled, the Home bridge schedule is ON, or the thermostat isn’t set to Eco mode.

  • Home/Away setting isn’t enabled
  • Home bridge schedule is ON
  • Thermostat isn’t in Eco mode


Home/Away setting isn’t enabled

When the Home/Away setting isn’t enabled, the Nest thermostat is likely to turn the AC OFF. Enabling this setting along with the Auto-Away setting activates Geo-fencing so that the thermostat identifies your location based on the GPS of your phone. This will prevent the AC from being turned OFF when you are at home.


Home bridge schedule ON

If this setting is turned ON, it overrides the Auto-Away setting and turns the AC down even when it’s not required to do so. It’s a good idea to turn this setting OFF when you’re not around.


Thermostat not in Eco mode

If this mode isn’t ON, the thermostat tends to turn the AC down. When this mode is permanently ON, the problem is resolved.


Nest thermostat turns ON AC instead of heat

This problem could be mainly because of the wrong wiring connection. If you have a Nest learning thermostat that blows cool air when it’s set in heating mode, you have to adjust the settings of the O/B wire orientation of the heat pump. You can do this by following the steps given below.

  1. Press the ring on the thermostat so that you can access its menu.
  2. Turn the ring around and select Settings from the menu.
  3. Select the Equipment option.
  4. Press the Continue option twice.
  5. Choose the Heat Pump option. The thermostat is set to the O orientation by default for heat pumps.
  6. Choose the B option if the default O option is selected and vice versa.
  7. Test the cooling and heating again to ensure that the problem is solved.

If the above steps don’t work, switch OFF the power connection to the heating and cooling system. Disconnect the wire connection to the O/B connector. Make sure that the wire isn’t bent and the copper wire is exposed by about one-third to half an inch. If not, strip the wire to the desired length.

Connect the wire back into the thermostat connector and fit the display. Turn ON the power and check the heating and cooling actions.


Why is My Nest Not Cooling?

Your Nest may not be cooling because of incorrect O/B wire orientation, a bad or bulged capacitor, a non-working condenser, or if the thermostat is defective.

  • Incorrect O/B wire orientation
  • Bad or bulged capacitor
  • Non-working condenser
  • Defective thermostat


How to Fix a Nest that’s Not Cooling

The steps involved in fixing a Nest that’s not cooling depends on the problem. You can try the steps given below to resolve the issue.

  1. Change the O/B wire orientation. You can follow the steps given in the section above to do this change.
  2. Inspect the thermostat for a bulging capacitor or malfunctioning condenser. Replacing the faulty component solves the problem. You can spot a defective condenser by an odd noise coming out of the Nest or by the very little cold air coming from the vents.
  3. Jump the Y and RH terminals on the thermostat and check if the outdoor unit turns ON. If so, the thermostat is faulty and has to be replaced. If it doesn’t and you hear a mild buzz from within the unit, the problem is with the unit.

Also, check for the power rating when the terminals are jumped. If you don’t see any issues here, you’ll have to look into the wiring as there are chances of incorrect wiring.


Why is My Nest Not Heating?

Your Nest may not be heating due to improper O/B wire orientation, a missing C wire, or because the thermostat is too close to a heat source.

  • Improper O/B wire orientation
  • Missing C wire
  • Thermostat too close to a heat source


How to Fix a Nest Not Heating

You can try to fix a Nest that’s not heating by following these steps.

  1. Reverse the O/B wire orientation by following the steps mentioned in the “Nest thermostat turns on AC instead of heat” section.
  2. Hook up a C wire to the AC. This is likely to help address the problem.
  3. Check if the thermostat is located close to a lamp or any other heat-emitting source. This could make the thermostat interpret that the house is warmer than it is. You can consider repositioning the thermostat to a location away from the heat source.

Take the thermostat off the base. Disconnect the white and red wires from their base terminals. Twist the two loose ends together tightly. If there is no hot air with the short connection, the air conditioner may be faulty. If you experience the hot airflow, the problem is with the thermostat.


Nest Turns OFF AC before reaching temperature

Your Nest is likely to turn the AC OFF before reaching its temperature because of two main reasons. These are:

  • Airwave mode
  • Loose connection
  1. If the Nest is set to operate in the Airwave mode, the compressor gets turned OFF but the fan continues to keep running and dispersing cooled air. Therefore, the thermostat is likely to sense that the room is already cool and will turn the AC OFF.
  2. There may be one or more loose wire connections in the thermostat. Identifying such connections and tightening them can help solve the problem. This is also a good chance to check for any incorrect wiring.


Why is Nest thermostat 10 degrees off?

Your Nest thermostat is often 10 degrees off because of a resetting problem, a malfunctioning humidity sensor, incorrect sunblock setting, nearby heat sources, or a network connection problem.

  • Resetting problem
  • Malfunctioning humidity sensor
  • Incorrect sunblock setting
  • Nearby heat sources
  • Network connection problem


The following are some ways you can address the above problems.

  1. Try resetting the thermostat using the Reset option under the Settings menu and following the instructions on the screen. You will often have to press the display and hold it down for about 10 to 15 seconds. Release the pressing action when the Google logo appears on the screen.
  2. If your humidity sensor isn’t working properly, your thermostat may feature an OFF reading. Getting the sensor replaced can help. You might want to check if the base of your thermostat also needs a replacement.
  3. Verify the Sunblock setting and ensure that it is ON. You can activate this setting under Nest Sense in the Sunblock menu. It will take a few days to adjust the room temperature taking into account the sunlight present in the room.
  4. Keep the thermostat in a different location that is ideally away from heat sources such as appliances, electrical outlets, and air vents with warm air circulation to mention just a few.
  5. Check the network connection of the thermostat. In some cases, the Wi-Fi chip of the thermostat tends to get overheated resulting in incorrect ambient temperature reading. In such cases, disconnect the thermostat from the network for a day and keep a tab on the ambient temperature. If the temperature reverts to normal, the Wi-Fi access point is responsible for the heat generation.


Nest turns ON fan but not AC

Your Nest may turn ON the fan but not the AC because of a faulty Nest base plate, no forced air circulation, a defective Y1 terminal on the thermostat, a missing C wire, or activated Air wave setting.

  • Faulty Nest base plate
  • No forced air circulation
  • Defective Y1 terminal
  • Missing C wire
  • Activated Air wave setting

If you notice the thermostat turning ON only the AC without the fan, you can try doing the following.

  1. Get the base plate of the thermostat replaced. A faulty base plate is one of the reasons that triggers this problem.
  2. Ensure that the forced air setting is activated. You can do this through the Equipment option in the Settings menu.
  3. Check the Y1 terminal of the thermostat for malfunctioning. If so, remove the defective one and fit a new one in its place. Sometimes, it may be the AC converter fitted to the AC unit that is defective and needs to be changed. This AC unit is connected to the Y1 terminal.
  4. Check if the thermostat is missing a C wire. If it is not there, it might be worth getting a C wire connection done.
  5. Check if the Air wave option under the Nest Sense setting is activated. Turning this OFF usually resolves the problem.


Why Nest Thermostat isn’t turning ON air conditioner unit

Your Nest thermostat often doesn’t turn ON the air conditioner unit because it’s set to Heat mode or there is a missing C wire. Sometimes, the system circuit breaker or fuse may need to be reset or replaced.

  • Heat mode setting activated
  • Missing C wire
  • Reset or replacement needed for the system circuit breaker or fuse


You can try out the tips given below to turn ON the air conditioning unit with your Nest thermostat.

  1. Check whether the thermostat is set to operate in Heat mode. If so, change it to Cool mode. Consider lowering the temperature setting to about 5 degrees lesser than the present temperature. You’ll sometimes have to wait for about 5 to 10 minutes for the setting to take effect.
  2. The thermostat is most likely missing out on a C wire connection. Often, this connection isn’t present in most thermostats. However, including this helps the unit to function more effectively.
  3. Check if the thermostat has a blown-out fuse or a defective circuit breaker. Do a replacement of the malfunctioning component.


AC fan won’t turn OFF with Nest

The AC fan may not turn OFF with a Nest thermostat due to the fan schedule setting, a power supply to the HVAC system, ora pending thermostat reset.

  • Fan schedule setting
  • Power supply to the HVAC system
  • Pending thermostat reset

You can do the following steps if the AC fan doesn’t turn OFF with a Nest thermostat.

  1. Check the fan schedule setting to see if it’s set to be always ON. If so, you should consider turning it OFF. In some cases, turning the schedule OFF and then ON again solves the problem.
  2. Disconnect the power supply to the HVAC system. This can help to fix the problem of the fan not turning OFF.
  3. Reset the thermostat to restore the factory default settings. This will stop the fan from being constantly ON.
  4. Remove the Nest from the wall. If you notice that the fan has stopped spinning, the thermostat is problematic and has to be changed. If the spinning continues, there may be an internal furnace or stuck relay issue that needs to be addressed.


Nest thermostat not turning ON AC compressor

Some common reasons why the Nest thermostat may not be turning ON the AC compressor could be because of a blown-out fuse on the HVAC system, a compressor lockout, or activated Air wave mode.

  • Blown-out fuse on the HVAC system
  • Compressor lockout
  • Activated Air wave mode


The tips given below can help to solve the problem of the Nest thermostat not turning ON the AC compressor.

  1. Check the HVAC system for a blown-out fuse and do a replacement if needed. This often happens if the C wire is inserted into a wrong connector.
  2. There may be a compressor lockout. In this case, replacing the compressor is a good solution.
  3. Check if the Air wave option has been turned ON. If so, turning it OFF can do the trick. This option can be found under the Nest Sense setting.


Why Nest thermostat is short cycling the AC

The Nest thermostat may short cycle the AC due to low level of refrigerant, a missing C wire, or a faulty thermostat.

  • Low level of refrigerant
  • Missing C wire
  • Faulty thermostat


The following tips can help you solve the above issues:

  1. Check if the AC unit is low on refrigerant. If so, fill it up to the required level. This is a good time to check for a refrigerant leak as that can also affect the compressor.
  2. Get a C wire installed in the right connector. This will stop the short cycling process most of the time.
  3. The thermostat could be defective. Replacing with a new one may address the issue.

Ernie Lo

Ernie Lo is a qualified web designer and web developer. He works as an IT support technician and website manager at Benleigh Vending, and he also fixes vending machines.

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