How to Troubleshoot an Air Handler Float Switch

HVAC units generate condensation when cooling.

The float switch, a safety device that shuts the system down when condensation overflows into the drain pan, can fail for a number of reasons, according to Smith. The good news is that it can be troubleshooted. Many homeowner insurance policies cover the damage to your ceiling.

1. Turn off the HVAC system using the circuit breaker.

2. Drain the water out of the drain pan. Use a bucket and cup for scooping the water out if the pan does not have a drain valve.

3. Locate the float switch and verify it is mounted in the drain pan. Typically, the switch is located on the same side as the air handler's access doors and is attached to the side of the pan. The switch can become dislodged if accidentally bumped.

4. Check the movement of the float arm on the float switch. It is a small metal arm protruding out of the main body of the switch with a piece of foam attached to the end. The arm connection inside the switch is delicate and sometimes binds during installation. The mechanical section of the switch is defective if the arm does not lift easily and makes a light clicking noise when it nears the top of the switch.

5. Turn the HVAC circuit breaker on and set the thermostat to run on "Cool." Lift the float arm on the float switch while the system is running and hold it for at least 1 minute. Some systems have an internal time delay on the blower and will continue to run for 30 seconds to 60 seconds after receiving a low voltage signal to turn off. The electrical section of the switch is defective if the system fails to shut down.