Why Does My Air Conditioner Stop Working When the Temperature Is High?

Thermostats

• Thermostat settings or locations may be responsible for seeming malfunctions. Adjusting the setting may be a foregone conclusion, but thermostat location plays an important role. Wall-mounted thermostats may sense cooler conditions than actual room temperature, if an air register is aimed directly at it, or the wall nearby. Close or adjust the register closest to the thermostat to rectify this situation. Move furniture or window treatments that may misdirect frigid air to a window unit.

Deep Freeze

• The condensed water that forms on the cooling coils of the evaporator must drain away completely. Water that pools at the bottom of the evaporator freezes, and the ice builds vertically. A temperature sensor in the coils "feels" the icy coldness and shuts the unit off, regardless of room temperature. Clear the condensation drain and use the fan setting to thaw the ice. Mount window units at a slight outward tilt to accommodate condensate drainage.

Light Freeze

• Evaporator coils can also freeze up from lack of air flow. However, the ice is lighter and quickly thaws after the unit stops. Normal operation resumes quickly, but the process repeats without cooling the room. Clean or replace clogged intake air filters to ensure good air flow over the evaporator. Remove the louvered intake register to access the filter of central units. Remove the filter from window unit cabinets to clean by washing or vacuuming.

Air Apparent

• Move household items or furniture away from the intake register of a central unit to avoid restricting air flow, or inadvertently adding aromas to the recirculated air. Tie back any curtains or drapes that may block the intake grill of a window unit. The refrigerant on the inside of the unit is cooled by the coils on the outside. Inspect the outdoor portion of the air conditioner to ensure no structures or landscaping obstruct or restrict air flow of the condenser coils.