HVAC Preventive Maintenance Procedures

One of the most important features in any home is the air conditioning and heating system, also called the HVAC (heating, ventilation and air conditioning) system.

The Filter

People do not usually think about their furnace or air conditioner until that equipment stops working. Then, fixing them become the most important thing on the "to do" list. There are a few simple things a home owner can do to help prevent having to call a repairman.
Cheap filter

The best place to start is at the inlet of your system. A high-quality filter in an easily accessible location is the best arrangement to ensure that your air system stays clean inside. The dust and allergens that can accumulate in an unfiltered return air chase can become a breeding ground for dust mites and the cause of many respiratory irritations. If you have an unfiltered return air duct, call an HVAC contractor to install a properly sized filter-grille. When choosing a filter, remember that if you can see through it, dust and crud can get through it easily. Pleated media filters are better than spun fiberglass ones. Filters should be changed every 30 to 60 days depending on the amount of fan run time. A visual inspection should tell you whether or not the filter is dirty. Write the date on the filter every time you change it to help you keep track.

The Drain

A serviceable heat-pump drain

Air conditioning or heat pump systems make water; in fact, some systems can make up to a gallon of water in just two hours. Ceilings have been ruined by water that did not drain properly from systems located in an attic, and repairs can be costly. It is important that the drain for your HVAC system is arranged in a serviceable way. Included is a drawing of the proper arrangement for a serviceable drain. "A" is the air conditioner cabinet, "B" is a short drain outlet and "C" is a removable cap to insert a cut piece of 5/8-inch water hose. With a strong blow of air, you can clear most clogs, or use a wet/dry shop vac. On the illustration, "D" is the "trap" to be filled with a 50% bleach/water solution to keep the unit from drawing sewer gas into the return air side of the A/C unit. "E" is an open vent that helps prevent gurgling bubbles, which may hinder drainage. Notice that "F" is lower than "B."

The Condenser Coil

The outside portion of your A/C or heat pump system is called the condenser. Air is drawn through the condenser coil using a powerful fan. As the air is drawn through the coil, dust, grass clippings, cat hair and leaves can accumulate on the coil, reducing both airflow and heat transfer. Once a year, it is recommended to gently wash out the HVAC coil. A weak dish soap solution with water can be applied to the unit while the power is turned off. Then, use a spray nozzle on the end of the water hose to wash off any accumulation. Do not use any type of high pressure washer to clean your coil, as the fins are thin and can be bent, which can restrict air flow.

The Contactor

The outside unit is subject to insects crawling inside it and causing problems. In the southern states, fire ants have been the cause of many service calls. They are attracted to the high voltage electric plates of the contactor, which turn the condenser on and off. The ants or other bugs get between the plates and keep the circuit from being made. The best thing to do is keep insects out. A heavy dose of fire ant or general pest control granules can be poured around the condenser pad as a barrier. With the fan off, some granules also can be poured inside the housing.


To check how well your unit is working, you can measure the temperature difference between the air going into your indoor unit and the air coming out. Turn your A/C to the cool position and to its coldest setting, and let it run for at least 10 minutes. With a thermometer that is easy to read, go to the air intake or return air, where your filter should be. Leave the thermometer to sense the temperature for at least 2 minutes, and make note of the temperature. Next, go to one of the supply registers and put the probe into the register, being careful not to touch the probe part of the thermometer. Again, let it sense for at least 2 minutes. Subtract the temperature of the supply air from the return air. If the unit is working well, the difference will be between 15 and 21 degrees F. If the range of difference is less than 12 degrees, a repair service should be called. The same procedure can be performed for heating, but the air coming out of the register needs to be at least 20 to 30 degrees warmer than the air going in.

Inspecting Ventilator Belts

Ventilator Drive Belt

Turn off the power before reaching in to check the condition of your belt-driven ventilator. Under normal conditions, belts will last about a year. If the belt is starting to squeal when the motor starts up, that is a good indication that it is time for replacement. The belt size is usually printed on the outer side of the belt, and auto parts stores carry a variety of sizes. If they do not have the size you need, they can usually order it, but order a couple. Keeping a second belt on hand can minimize downtime in case of breakage.

About the Author

Susan King is a teacher with 27 years experience with all ages, grade levels and ability levels, including teaching in China. She has written a book, "The Road to Rebecca," about adopting from China. She graduated from Texas A&M University. She also has a ThM from Colorado Theological Seminary in Christian Counseling and recently received her PhD.