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

What might cause short cycling of the compressor and condenser fan motors while the blower motor is not running?

1. A faulty compressor relay

2. A faulty blower motor or blower relay

3. A blocked return duct

4. A low refrigerant level

The correct answer is: A faulty blower motor or blower relay

Short cycling of the compressor and condenser fan motors can occur due to several reasons, but one key cause is related to issues with the blower motor or blower relay. When the blower motor is not functioning, it fails to circulate air properly across the evaporator coil. This lack of airflow can lead to the coil freezing, which, when it thaws, can cause the compressor to shut off prematurely to prevent damage. In this situation, the compressor and condenser fan motors may start and stop frequently (short cycling) due to the system attempting to maintain the desired temperature without adequate airflow from the blower motor. The relay, responsible for sending power to the blower motor, could also fail, resulting in the blower motor not operating despite the call for cooling. While other options may present issues in an HVAC system, they do not directly relate to the scenario of short cycling primarily caused by inadequate airflow produced by the blower motor. This makes the relationship between the blower motor (or its relay) and the short cycling phenomenon a significant factor in HVAC performance.