Heating, Ventilation, and Air Conditioning (HVAC ) Electrical Practice Test

When does the crank case heater operate in the schematic?

1. When the compressor is off

2. When the compressor is running

3. Only during defrost cycles

4. Continuously with power

The correct answer is: When the compressor is off

The crankcase heater is an essential component in HVAC systems that helps prevent the accumulation of liquid refrigerant in the compressor during periods when it is not operating. Therefore, it operates primarily when the compressor is off. This functionality is crucial because if liquid refrigerant enters the compressor, it can lead to hydraulic issues and damage the compressor when it attempts to start up again. Having the crankcase heater activated during the off cycle warms the compressor and helps vaporize any liquid refrigerant that may have accumulated, ensuring that only vapor enters the compressor upon startup. This processes protects the compressor and enhances the overall efficiency and longevity of the HVAC system. In contrast, operating the crankcase heater while the compressor is running, only during defrost cycles, or continuously with power would not address the specific issue of preventing liquid refrigerant from entering the compressor during its inactive state, leading to potential mechanical failures and inefficiencies.