MU Extension MU Extension       University of Missouri    ●    Columbia    ●    Kansas City       Missouri S&T     ●    St. Louis -Housing


Feature Articles - Housing


Air conditioner needs regular maintenance to be efficient


Central air conditioning systems need regular maintenance to perform at peak efficiency.


Things like low refrigerant levels, dirty fans and filters, loose or worn belts, and clogged condenser coils can seriously hinder the A/C unit’s cooling ability, said Bob Schultheis, natural resource engineering specialist with University of Missouri Extension.


“Doing an air conditioner tune-up will not only help you stay cooler and more comfortable, but the unit will use up to 30 percent less electricity, increase its service life beyond the average 10 to 15 years, and help prevent mold from developing in the system,” said Schultheis.


If your air conditioner is several years old, has never been cleaned or is not cooling, a qualified service person may be needed to perform the necessary maintenance.


However, replacing filters, cleaning thermostats and fans, and removing grass and debris from outdoor condenser coils are well within the skill level of many homeowners.


“To reduce the frequency of future cleanings, avoid discharging grass from the lawn mower toward the condenser unit when mowing the yard, and plug air leaks in the home so the A/C unit runs less often,” said Schultheis.


Schultheis also offers this advice for homeowners:


  • Before doing any work on the A/C unit, disconnect the electrical power to it at the service panel by shutting off the breaker or pulling the fuse. Confirm the unit is off by setting the thermostat switch to the constant fan or on position. If the unit remains off, you’re ready to proceed.
  • Cleaning the thermostat depends on which of the three types it is.
    1. Bi-metallic types have two contact points that can be gently brushed of dust after removing the thermostat cover. Slide a clean piece of paper between the contact points to rub off any remaining dirt. Do not use sandpaper.
    2. Mercury-bulb types have contact points that are not accessible because they are sealed within a glass bulb. Use a small level or plumb bob and line to check that the thermostat is positioned level on the wall. Adjust the wall mounting screws if it is not.
    3. Electronic types need no adjustment.
  • Filters on indoor blower unit systems should be checked monthly during the cooling months, and should be replaced or cleaned of dust and pollen as needed. There are generally four types of filters.
    1. Disposable stranded fiberglass filters are least expensive, but also least effective at filtering.
    2. Replaceable pleated filters are somewhat more expensive, but do a much better job of keeping the indoor air clean.
    3. Reusable filters of metal mesh or nonmetal fibers can be cleaned by vacuuming and then washing in warm water with a mild detergent. After allowing the filter to dry, spray it with a dusting spray to help it better collect airborne dirt.
    4. Electrostatic or electronic air-cleaner filters should be cleaned according to factory recommendations shown in the owner’s manual or by contacting the dealer.
  • Most motor bearings on the blower unit are permanently lubricated, with the fan directly attached to the motor driveshaft. If the motor has oil cups on each end, apply three drops of 10-weight oil to each one. Refer to the manufacturer’s instructions for cleaning the blower blades. Unless there is easy access to the evaporator coil (or A coil), cleaning of this coil is best left to a qualified service person.
  • The outdoor condenser coil works like a car radiator — it expels heat. It cannot do that if the coil fins are clogged with debris. Carefully remove only as many screens and panels as needed to gain access to the coil fins, and note how the parts go together for later reassembly. Brush debris from the fins with a whisk broom, taking care not to bend the fins. If the dirty side faces out, use a garden hose and nozzle with a narrow water stream to wash the fins in a downward motion. Avoid getting water inside the unit where electrical components could be shorted out. Wait 15 minutes to allow drying before reassembly and turning the unit back on.


For more information about home energy conservation, contact the nearest University of Missouri Extension Center or go online to and do a keyword search for “home energy.”


University of Missouri logo links to

Site Administrator:
Copyright  ADA  Equal Opportunity

MissouriFamilies is produced by the College of Human Environmental Sciences,
Extension Division, University of Missouri


Last update: Monday, May 15, 2017