Roof Top A/C Unit Is Not Cooling

Filters and Vents

• A rooftop unit does not encounter the same debris (like leaves) that blows around close to the ground, but that doesn't mean it is dust-free. Many rooftop units are left alone so long that their filters become clogged with dirt. This slows air flow and prevents proper cooling. Larger pieces of debris can be caught in the vents themselves and lead to the same problem.

Evaporator Coils

• Evaporator coils are the component that releases heat into the outside air. But because these coils are exposed to air flow, they are also exposed to the dust and cold. A thick layer of dust or frost can render the coils ineffective, keeping them from releasing heat and keeping your system from cooling down properly. Cleaning the coils can help solve this problem.

Pumping Systems

• Your condenser uses a pumping system to compress the refrigerant gas. If this system starts to fail, the condenser will no longer do its job, and the pumping system must be replaced for the system to work properly again. Likewise, the refrigerant lines may have sprung leaks unnoticed up on the roof, and low refrigerant pressure could be contributing to the problem.

Temperature Control

• Check your AC settings to make sure they are within the proper range. If they are, there may be a problem with your sensors or thermostat wiring. This is difficult to check without accessing the roof unit and then using an ohmmeter, so you may want to call a maintenance specialist for a checkup.