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Air Conditioner

Air conditioners come in two forms: window or central air. Window air conditioners are most common in apartment complexes or older homes. Central air conditioners are found in most newer homes or business buildings. Central air is much better at providing a balanced temperature throughout all rooms. Window units tend to only cool one room and do not circulate are very well.

Regardless of the system, both types work in a similar fashion. The thermodynamic process is reliant on a chemical called refrigerant 22 (i.e. R-410a is growing in popularity) to transfer heat from the inside of the house to the outside. To accomplish this goal the refrigerant undergo phase, temperature, and pressure changes through three devices: compressor, condenser, and evaporator. The refrigerant will leave the house in a cool low-pressure gaseous state. Then the compressor forces the molecules close together to dramatically increase the temperature and pressure.

The condenser, or heat pump, located on the outside of the house will cool off the refrigerant. This may seem counterintuitive when the temperature outside is very hot, but the compressor raises the temperature of the working fluid to much higher temperature. The little metal fins covering the tubing and the blower increase the amount of heat transfer between the condenser and the outside air. This drops the temperature of the refrigerant enough to turn it into a liquid. It is also much cooler but is still at a high pressure.

The fluid travels back inside the house to the evaporator, which often a part of the furnace system for homes with central air. Here the fluid goes through an expansion and back to a gaseous state. During this phase change the refrigerant soaks up heat from the passing by air. The fluid is contained in metal tubes but takes in the heat through a metal finned heat exchanger. The air will return to the house through to help cool and the refrigerant will go back to the compressor to start the process all over again.

This process is great for cooling air and is not only utilized in air conditioners but also in freezers and refrigerators.

Air Conditioner Maintenance Checklist

At least once a year before the summer the air conditioning system should undergo a full inspection and maintenance routine. Keeping the heat exchangers clean and the system full charged with refrigerant will ensure your unit operates efficiently.


The condenser is the outside part of the system. The biggest problem here is the dirty and damaged heat exchanger fins. The small metal fins on the heat exchanger promote better energy transfer but become inhibited by damage, dust, and corrosion.

The following steps are good for cleaning the heat exchanger, but consider calling a professional to have the line pressure checked if you suspect a leak or the system isn’t cooling properly. Also, the checklists below are for a central air system but can be easily adapted for a window unit.

  • Start by inspecting washing grass, leave, dirt, and other debris off the unit with a garden hose. Make sure it is on a mist setting or the fins will be damaged.
  • After letting it dry, use a coil cleaner designed for AC fins. Spray the solution on the fins and let it set for the specified time period (usually 5-10 minutes). Then spray the solution off with a hose on the mist setting.
  • Inspect the heat exchanger for any bent fins. Use a putty knife to carefully straighten out the delicate fins. It is possible to buy a fin comb designed for your unit to make this process easier.
  • Inspect the metal tubing going to and from the condenser. Look for oily drops that may indicate a possible refrigerant leak. Call a professional if a leak is detected.
  • Trim back any bushes or tree branches that are growing close to the condenser.


The evaporator is the inside part of the air conditioning system. The easiest way to keep this section clean is to regularly replace the air filters.

  • Remove the access panel and clean the dust off the air duct surfaces
  • Use the same coil cleaner as the condenser for the heat exchanger fins in the evaporator.
  • Let it set for the specified time and then clean with water in a spray bottle. You may need to refill the bottle several times to make sure you completely wash off the coil cleaner.
  • Put the access panel back in place.
  • Verify that the water runs freely from the drip pan down the drain. Dump 2 cups of bleach down the drain to clean out any possible mold growth that may plug the pipe. Follow it up with 4 cups of water.
  • Inspect the metal tubing running to and from the evaporator for oily drops that may indicate a leak.

References: 1 - EnergyQuest

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