Nest Thermostat Not Turning on AC Compressor [Solved]

If you are dealing with a Nest thermostat not turning on ac compressor, then this troubleshooting guide is for you. It can be quite frustrating to discover that your ac compressor can’t turn on to cool your living spaces and this could leave you feeling uncomfortable.

Some reasons why your Nest thermostat won’t turn on your ac compressor include

  • Incorrect thermostat settings
  • Problems with power
  • You have an ac capacitor that is defective
  • Your ac contactor is not working fine.
  • Your compressor died (In the worst-case scenario)
Nest Thermostat Not Turning on AC Compressor
Nest thermostat

Read also: Fan Kicks on But Compressor Not Working [Solved]

Why is My Nest Thermostat Not Turning on AC Compressor?

Let’s jump right into issues that can prevent your nest thermostat from turning on your ac compressor.

Incorrect Thermostat Settings

If your Nest thermostat is not set to ‘cooling’ mode, it won’t turn on your compressor. Sometimes your thermostat can be on ‘cooling’ but if your temperature is set above your current temperature reading, your ac won’t start.

To start your ac compressor, set the point below the current room temperature reading.

To completely rule out thermostat issues, check how your thermostat was programmed. Ensure it was correctly programmed. If it wasn’t, try reprogramming your thermostat so that your ac can start cooling.

Problems With Power

Another possible reason your ac compressor won’t start with a nest thermostat is that there could be power cut to your outdoor unit. Your outdoor condenser unit can be cut off from power if

  • The circuit breakers tripped
  • If the power switch(disconnect) was pulled out from its position
  • Your ac contactor is defective

Tripped circuit breakers

Tripped circuit breakers could be the reason your Nest thermostat is not turning on your ac compressor. Occasionally, breakers can trip due to a compressor lock out or a power surge. When that happens, the problem can easily be fixed by resetting your circuit breakers.

If the breaker trips twice then call a licensed HVAC technician to come and do a thorough test on your ac system for any other issues.

Disconnect Pulled Out

Other power issues that could prevent your ac compressor from turning on include, a ‘disconnect’ that is switched off. A ‘disconnect’ is a device that cut power when maintenance or other works are being done on your ac outdoor unit.

If you have had someone do some works on your HVAC system, they might have disconnected it and forgotten to put it back. You can check it, to rule it out.

Other times, your ‘disconnect’ can also be equipped with a fuse or two. If yours has a fuse, check that the fuse is not blown out. If there is no noise coming from your outdoor unit when you turn it on with your thermostat, you’ll need to check if your ac contactor is working.

Bad AC Contactor

A contactor powers up your outdoor unit when there is a call for cooling or heating. However, though rare, this device can become defective. If it becomes defective, your ac compressor won’t turn on.  If you try turning on your ac from your thermostat and there is no sound coming from your outdoor unit, your ac contactor might be defective.

How do I know if my ac contactor is defective?

Open your ac unit cover with a screwdriver. A contactor looks like one in the picture below.

bad ac contactor

Actually, you can either have a dual pole or a single pole contactor. Try manually contacting the two contactor plates (You can turn on your ac at this point.) If your compressor and fan start, then your problem was with a contactor. If not, check your ac capacitor.

Bad AC Capacitor

A bad or failed ac capacitor is among the commonest reasons for an ac compressor that is not turning on. Capacitors store energy and supplies the compressor with the needed energy to start running.

If your capacitor is dead, your compressor won’t start when you try turning on with your thermostat.

Sometimes it’s easy to spot a capacitor that has failed. It will have a swollen top. Other times you’ll need a multimeter to test it for continuity. Anyway, the bottom line is, if your capacitor is dead, you’ll need to replace with a working one.

These days ac capacitors are readily available, and you can get yourself one online. Take note of the model information to ensure you buy the right model.

Also read: AC Compressor Working but Not Cooling [Solved]

Dead Compressor

The problem you probably don’t want to hear about is a dead ac compressor. If you have had that compressor for a really long time like 10 years, it’s possible that it has served its purpose for your home and needs a replacement.

Even though compressors a designed to work throughout the life of your air conditioner, they can die when you least expect them to. When that happens, you’ll have to replace your compressor or replace the whole ac system. You can get quotes for both options.

If your think replacing your ac compressor will be costly which in most cases is, I’ll recommend you replace the whole ac system. Specifically, if the cost of replacing your compressor is more than half the cost of replacing the whole ac unit.

Things you can do to increase the life of your ac compressor

  1. Regular maintenance: having schedule and regular HVAC maintenance will keep your heating and cooling systems working efficiently and with less problems. Regular maintenance will also prevent unexpected and costly HVAC breakdowns.
  2. Replacing your filters on time. Clean air filters help your HVAC system to work without strain. But if your air filters stay clogged, this can negatively affect many components of your HVAC system including your compressor. Typically, air filters should be cleaned or replaced at least once in 2 months.

Final Thought

We hope this guide on dealing with a Nest thermostat not turning on ac compressor has been helpful. If you still can’t figure out how to resolve the problem after reading this article, its best to call your local HVAC technicians. They should be able to fix this for you in no time. Thanks for reading.

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