If a condensing unit short cycles, and is not low on refrigerant with a hissing sound in the expansion valve and a cold liquid line, what is the likely cause of the trouble?

When a condensing unit short cycles—meaning it turns on and off rapidly—there can be several contributing factors. In this scenario, the symptoms include a hissing sound at the expansion valve and a cold liquid line, with the assurance that the system is not low on refrigerant.

The diagnosis points to the liquid line shut-off valve being partially closed as the likely cause of the trouble. When the shut-off valve does not fully open, it restricts the flow of refrigerant to the expansion valve. This can lead to insufficient refrigerant entering the evaporator coil, causing the system to operate inefficiently. The hissing sound is typical when there is a restriction or a high-pressure situation at the expansion valve, where refrigerant is trying to pass through but is impeded. The cold liquid line indicates that while refrigerant is present, it's not moving as it should due to this blockage, leading to short cycling as the system attempts to reach the desired temperature and continuously struggles to do so.

This situation contrasts with the other options provided. A faulty thermostat could lead to inappropriate cycling but would not explain the hissing or the cold liquid line. A clogged filter would typically cause issues related to airflow or reduced efficiency rather than the specific symptoms observed. Lastly