My Central Air Unit Is Making a Hesitation Noise: What Is That?

Hesitation Noise at End of Cycle

• An AC unit waits for a reading from the thermostat before it will stop running. Once it does have the signal to end the cycle, it first turns off the compressor, but the pump remains on for a minute or so while it is removing the last of the cool air. This can cause a hesitation noise, which is completely normal.

Hesitation Noise while Heating

• An AC unit simply reverses its processes when it heats air during the winter. Cold air comes into the machine and the unit heats it. During the process, the outer coils will occasionally freeze. When this happens, the unit will switch back into cold mode and melt the coils while simultaneously running air past heat strips to warm it. This process makes a very loud hesitation noise that almost sounds like the machine is broken.

Hesitation Noise while Changing Cycles

• For the unit to go from hot to cold, it must first shut down, reverse the fans and then start back up again. This process typically takes around 45 seconds to 1 minute, but will sound like the machine is hesitating. To avoid strain on the machine when switching cycles, it's beneficial to turn it off first and then switch it to another cycle once the machine is completely off.

When to be Concerned

• While most noises are very normal with a central air unit, there are some problems to check for if the noise seems concerning. First, check the temperature in the room. If the temperature has either went up since you last checked or has not moved, the AC unit may be malfunctioning. Next, check the temperature of the air coming from the unit. If the air feels warm, then the machine may be completely frozen. Turn off the machine, replace the filter and allow to thaw for 24 hours.