Why Isn't Your Compressor Turning On?

Your compressor is one of the most expensive and most critical parts of your home's air-conditioning system. When warm, gaseous refrigerant returns from the evaporator, the compressor turns it into a hot, high-pressure vapor before passing it along to the condenser coils. Without compressing the refrigerant, it could not release heat from your home back into the environment efficiently.

The compressor effectively acts as a pump that drives the refrigerant cycle. If it isn't working, the refrigerant can't pass through your system, and you won't get any cold air. Compressor failures can be frustrating when they occur on hot days, especially since repairs are rarely cheap. Understanding why your compressor may not be turning on can help you better understand the potential solutions.

Common Reasons for Stubborn Compressors

If your compressor doesn't run at all or if it frequently shuts down, it's likely due to one of four general problem categories, listed here in order of increasing severity:

  • Signaling (thermostat) issues
  • Electrical issues
  • Overheating
  • Internal mechanical failures

For the compressor to operate, it needs power and a signal from the thermostat to request cooling. If your thermostat isn't functioning correctly, it may not signal the compressor to engage, or it may cause it to shut down too soon. Since thermostats are relatively inexpensive, they're an excellent place to start when diagnosing compressor issues.

Electrical problems are another common culprit. An old or failing compressor can draw too much power, tripping the circuit breaker. Additionally, the start or run capacitor may be faulty. If your start capacitor fails, the compressor likely will not engage at all. On the other hand, a bad run capacitor might cause the system to produce a loud humming noise, draw too much power, or shut down prematurely.

Your compressor might also shut down or fail to run if it overheats. A compressor that's too hot will usually trigger a safety switch to avoid causing additional damage. Compressors typically overheat due to other failing parts, such as faulty condenser blowers, clogged condenser coils, or frozen evaporators. Attempting to run an overheating compressor can result in more severe damage.

Finally, the compressor may have an internal mechanical failure. You'll usually need to replace your compressor if it's failing in this manner.

Resolving Compressor Woes

Avoid using your air-conditioning system if the compressor refuses to start or consistently shuts down. Forcing your system to run when there's an underlying problem can cause more damage to the compressor, potentially turning a relatively minor repair into a much more expensive one. If you can't determine what's causing your issue, you'll need an HVAC technician to help you diagnose and conduct air conditioner repair.