When an air conditioner's refrigerant enters the compressor while still in liquid form, it can destroy the compressor's motor. This is because most of the parts of the compressor are specifically designed to deal with the refrigerant when it is in gas form. Its presence in liquid form – liquid slugging – is usually a shock to the system. To help prevent this from happening, manufacturers usually fit air conditioners with a crankcase heater.

Crankcase heater and refrigerant migration

The crankcase heater's job is to simply ensure that the temperature in the crankcase is relatively higher than that of other parts of the air conditioning system. This is important when it comes to refrigerant migration control because the refrigerant has a tendency to migrate from warm areas to colder areas. And since the compressor unit is usually located outside, the final destination of this movement is usually the compressor.

The migration of the refrigerant into the crankcase is dangerous mainly because when the refrigerant reaches the area, it can condense and hence causing slugging. The heat generated by the crankcase is therefore effective when it comes to reducing the chances of this happening.

Crankcase heater and prevention of condensation

The crankcase heater also heats the oil that is available in the compressor. This usually keeps the temperature of this oil at a level that ensures that the refrigerant does not condense and mix with the oil. And as for any refrigerant that is already trapped in the oil, the heating effect of the crankcase heater will be enough to release any trapped refrigerant. This prevents the dilution of the oil, something that might have then caused the destruction of the compressor.

Crankcase heater failure and liquid slugging

There are two reasons why a crankcase heater can fail. The first reason is that the crankcase heater may simply burnt out. The second reason is that the system controls that are supposed to turn the crankcase may malfunction. In either of these cases, the crankcase will not only fail to prevent the migration of the refrigerant to the crankcase, but also be unable to force any liquid refrigerant from the oil in the compressor. This will then leave the air conditioning system at the mercy of liquid slugging.

To protect your system from damage, you should have the burnt out crankcase heater replaced. As for the malfunctioning system controls, having an air conditioner repair contractor check them for defects and loose wiring is advisable.