Nest Thermostat Not Cooling? 10 Easy Fixes

Quick Fix

Nest thermostat not cooling? Check if it’s set to Cool mode – tap the thermostat and turn the dial to set temperature below current room temperature. Verify the system is set to “Cool” not “Heat” or “Off”. Also check if your HVAC system’s breaker is on and the air filter isn’t clogged.

Why Won’t Nest Thermostat Cool?

Nest cooling issues stem from incorrect mode settings, dirty air filters, HVAC system problems, wiring issues, or software glitches. The thermostat may also show cooling but the AC unit itself may have issues.

Method 1: Check Thermostat Mode

Ensure it’s set to cool.

1. Tap the Nest display
2. Turn dial to see current mode
3. Ensure it shows Cool (not Heat or Off)
4. Set target temperature below room temperature
5. Blue color indicates cooling mode

Method 2: Check Air Filter

Clogged filter blocks airflow.

1. Locate your HVAC air filter
2. Remove and inspect for dirt
3. Replace if dirty or clogged
4. Replace every 1-3 months
5. Dirty filter can trigger safety shutoff

Method 3: Check Circuit Breaker

AC unit needs power.

1. Find your electrical panel
2. Locate AC/HVAC breaker
3. Check if it’s tripped (middle position)
4. Flip off, wait 30 seconds, flip on
5. Check indoor and outdoor unit breakers

Method 4: Restart the Nest

Reboot clears software glitches.

1. Press and hold Nest display
2. Hold for 10 seconds
3. Select Restart
4. Wait for Nest to reboot
5. Set to cool mode again

Method 5: Check Wiring

Loose wires prevent cooling.

1. Turn off HVAC breaker
2. Remove Nest from base
3. Check all wires are firmly inserted
4. Look for the Y wire (cooling)
5. Reattach and restore power

Method 6: Check Equipment in Nest App

Verify system is detected.

1. Open Nest app
2. Select thermostat > Settings
3. Tap Equipment
4. Verify cooling system shows
5. Run equipment test if available

Method 7: Check for Error Codes

Nest displays error messages.

1. Look for error codes on display
2. E73: No cooling detected
3. E74: Wiring issue
4. Check Nest support for specific code

Method 8: Check Outdoor Unit

AC compressor may be off.

1. Go to outdoor AC unit
2. Check if fan is spinning
3. Listen for compressor running
4. Check for ice on unit (refrigerant issue)
5. Clear debris around unit

Method 9: Factory Reset Nest

Clear all settings.

1. Settings > Reset > All Settings
2. Confirm reset
3. Set up Nest again
4. Reconfigure cooling system
5. Test cooling after setup

Method 10: Call HVAC Professional

System issues need expert help.

• If outdoor unit doesn’t run, compressor may be bad
• Refrigerant leaks need professional repair
• Wiring issues may need HVAC technician
• Annual AC maintenance prevents issues

FAQ

Why does Nest say cooling but AC not running?

Nest sending the cooling signal doesn’t mean AC will respond. Check the Y wire connection, verify the outdoor unit has power, and ensure the AC unit itself is functioning. The issue may be with the HVAC system, not Nest.

Why does my Nest keep switching from cool to heat?

This happens in Auto mode when room temperature is between heating and cooling setpoints. Set to Cool-only mode if you only want cooling, or widen the gap between heat and cool temperatures in Auto mode.

How do I know if Nest is compatible with my AC?

Use the Nest compatibility checker at nest.com/compatibility. Most 24V systems work. You need a C wire for reliable power. Nest may not work with some multi-stage or heat pump systems without an adapter.