Which of the following can cause a limit switch to open?

A dirty filter can indeed cause a limit switch to open. The limit switch in an HVAC system is designed to monitor the temperature within the system to prevent it from overheating. When the air filter becomes dirty, it restricts airflow through the system, causing the temperature to rise. If the temperature exceeds the set limits, the limit switch opens to shut off the system and prevent damage from overheating.

This mechanism is critical for system protection, as continuous operation in such conditions could lead to further issues, such as damage to the heat exchanger or other components. Therefore, maintaining a clean filter is essential for the system's proper operation and longevity. In contrast, while low refrigerant levels, system malfunctions, or power supply issues can lead to operational problems, they do not directly trigger the limit switch to open in the same manner as restricted airflow does from a dirty filter.