It is not abnormal for heat pumps to make loud noises particularly during winter. It’s because at this time, the reversing valves of the heat pumps are shifting the flow of refrigeration between cooling and heating modes. This process happens every time the heat pump unit goes through a defrost cycle.
As the shifting occurs, there is usually a loud swooshing sound that lasts for a number of seconds. This sound is at times followed by compressor noise that is also louder than normal as the heat pump refrigerant pressurizes to equalize. These noises have at times made homeowners to seek technical assistance because they think their systems are faulty.
Another type of sound which is very normal is whenever the outside condenser turns on and off. For several seconds, the sound emitted is like that of an out of balance washing machine.
The outdoor unit may produce a buzzing sound even when it is not running. This may also sound strange, but actually it shouldn’t because this sound comes from the reversing valve’s solenoid coil. The good news is that this is low voltage hence it doesn’t waste energy.
The metal to metal sound or rather a persistent thumbing sound may come from your outdoor AC unit if the fan blade of the compressor is hitting something such as a twig, wire, or ice. The best approach here is to shut off the unit so that your fan blade can be saved as well as your motor. These are components that are crucial to the operation of your AC unit and if they are thrown out of balance, your system will not only stop working, but also affect other components as well.
Isolation pads which need replacement can cause a vibration noise. Also, this noise could result from refrigerant lines that are tightly strapped.
Apart from the above reasons, below is a list of other causes of strange outdoor unit noises.
- Vibration due to loose parts
- Low refrigerant charge which gives rise to gurgling noise
- Defective compressor valves
- Defective motor
- Iced up outdoor unit
- Loud compressor
- Loud unit – The AC unit could be loud in itself and this cannot be repaired unless the unit is replaced.
- Bent or out of balance fan blades
For the more technical problems, it is advisable you contact professional HVAC experts. Remember, the company you hire to install and service your AC system will largely determine the degree of comfort that you enjoy.