My Central Air Is Blowing Hot Air; What Is Going On?

The Cooling System

• Central air conditioning is designed to cool your entire home in the same way your refrigerator cools the air that keeps your food fresh. Chemicals that easily change from a gaseous state to a liquid state transfer heat from the air inside your home and carry it to the outside for dissipation. The system consists of three main parts: the condenser and compressor located outside, and the evaporator found inside the home.

The Cooling Process

• The refrigerant arrives at the compressor in cool, low-pressure form. As the compressor squeezes the fluid, the refrigerant's molecules are packed closer together to form a hot, high-pressure gas. The gas moves on to the condenser, where it changes to a pressurized liquid. From the condenser, the liquid moves through a tiny hole into the evaporator. Pressure in the liquid drops and evaporation takes place. Evaporation requires heat, which it extracts from the warm inside air. The refrigerant leaves the condenser as cool, low-pressure air and the cycle begins again.

Possible Problems

• The thermostat that controls the temperature within your home governs heat in the winter and cool in the summer. A thermostat set to the heat mode will blow hot air. Ensure that the thermostat is set to cool as summer weather requires. Check and change your air filter every two months. A clogged filter will restrict airflow to the condensing coil and inhibit cooling. Eventually, a dirty coil may become a frozen chunk of ice. A tripped breaker or blown fuse may be preventing the condenser from working.

Compressor Issues

• The compressor inside the condensing unit is designed to shut down if it overheats. Cleaning the coils surrounding the condensing unit will prevent the restriction of airflow that may cause compressor failure. While you are outside, check to make sure the cooling fins are clean and the condensing unit is sitting level on its concrete pad. Call in certified HVAC technicians to replace faulty components or recharge refrigerant as required.

Heat Pumps

• Some homes have air conditioners that cool and separate furnaces for heat. Others have an all-in-one heat pump with a valve that allows the pump to be switched between air conditioner and heater. Heat pumps have hot coils on the inside and cold coils on the outside -- the reverse of stand-alone air conditioning systems. Periodically, the coils on the outside collect ice. The heat pump switches itself into air conditioning mode to melt the outside ice and turns on burners to heat the cold air that is pumping out from within. The pump returns to heating mode once the ice has melted.