You're probably used to the noises your air conditioner makes when it's running, so it can be alarming when your AC starts producing unusual sounds. A hissing sound from the AC is a common complaint from homeowners, and it can indicate a few different problems. This guide will explain three possible causes of a hissing noise near your central air conditioner.

1. Refrigerant Leaks

Refrigerant circulates under high pressure in central air conditioners. Refrigerant goes through a process of compression and evaporation to efficiently remove heat from your home's air. Leaks at certain points in the refrigerant loop will cause coolant to escape as a liquid. At other points, it may escape as a pressurized gas.

If a refrigerant leak is to blame, you will continue to hear a hissing noise even when your air conditioner is turned off. If refrigerant leaks aren't dealt with, your central air conditioner will gradually lose its capacity to cool your home. These leaks can be very small and impossible for homeowners to locate, so call an HVAC contractor to inspect your AC.

2. Duct Leaks

Just as pressurized refrigerant can make noise as it escapes, so can pressurized air inside your air ducts. Joints in your ductwork may loosen over time, or you may hear air escaping due to corrosion or punctures in your ducts. Duct leaks are a likely culprit if the hissing noise seems to be louder near your vent registers.

Unlike refrigerant leaks, noises caused by duct leaks will cease when you turn off your air conditioner and no air is moving through the system. Losing air from your air ducts means your AC will need to work harder to cool your home. This results in higher energy costs and less consistent temperatures from room to room. Professional HVAC contractors can use air balance testing to pinpoint the location of any leaks in your ductwork.

3. High Compressor Pressure

Sometimes, your central air conditioner can produce a hissing noise centered on the outdoor condenser. This is a sign that the pressure in the compressor is too high. High compressor pressure compromises the refrigerant system and may cause your AC to shut off if the system becomes unstable.

You will usually notice hissing sounds from high compressor pressure for only the first handful of seconds after you start your air conditioner. If these symptoms persist, you will need to hire an HVAC professional to diagnose the pressure bottleneck inside your AC condenser.

A hissing noise from your air conditioner isn't a problem you should ignore. If your central AC starts making unusual noises, call a local HVAC repair contractor to correct the problem and ensure your system is running efficiently.