Keep that HVAC system happy so you can rest easy

It doesn’t take an air-conditioning expert to know that a well-maintained central system will go a long way toward keeping your home refreshingly cool and free of mold and other contaminants. While major repairs to an HVAC, or heating, ventilation and air-conditioning system, are best handled by a pro, there are a number of preventive steps well worth a homeowner’s time.

First, the filters

A dirty air filter makes the system work harder, so keep yours clean. Even if a filter is rated for 90 days, it’s good to check and change them monthly during periods of heavy use.

Keep it clean

Outdoor AC Unit

The outside unit of a central system needs to be kept free of debris, but before you work on it, switch off the power to the unit at the breaker. Trim away grass and overgrowth, and remove piled up leaves and branches. To clean the condenser coils and fan inside, unscrew and remove the top and side panels of the unit, then carefully hose off the coil fins and fan. The fins can be cleaned more thoroughly with a soft brush — just don’t bend them.

No critters!

Mice chew on wiring and insulation. Dogs gnaw refrigerant lines because they’re cool and damp. Wasps nest in an outdoor unit, and ants can get in the electronics. Best advice: Keep pets away and treat at the first sign of ants or other invaders.

Clear Clutter

Keep the inside or blower unit of a central system free of clutter. Whether it’s in a closet or garage, in an attic or even beneath the floor, the area around it should not be used for storage.

Check for clogs

Finally, check the inside unit’s drains for clogs. If you find water on the furnace or pooling at its base, there’s likely a blockage that will need to be unclogged.

Quick Tip


Air filters are rated for efficiency at removing airborne particles with a number from 1 to 16 for MERV, or Minimum Efficiency Reporting Value. The higher the MERV, the smaller the particles the filter can trap. Be aware, though, that a filter with a high rating might actually overtax your system. Ask an A/C specialist if you’re unsure.

Let someone else take a look

AC Repair man inspecting unit

An annual inspection of your air conditioner might set you back up to $100. But it will seem like money well spent during the hazy days of summer. As Kenny Glover of Key Heating & Cooling explains: “Most people don’t think about maintenance for their air conditioning system. But they regularly check the fluid levels and change the oil on their car. Well, it’s the same concept only even more important for your A/C. … How well it works affects the very air we breathe.”

Service agreements offered by certified HVAC professionals generally cover an annual inspection of the electrical components, duct system, blower assembly, coils and drains. Thermostats, refrigerant levels and defrost cycles also will be checked. Extra charges typically involve any necessary parts, cleaning and topping off the refrigerant. Major repairs often qualify for a discount.

How Air Conditioners Work

Home AC diagram

Diagram of a simple window unit illustrates the cooling cycle.

Beyond the thermostat

When dealing with an HVAC system, it pays to have a basic understanding of how an air conditioner works — if only to avoid staring blankly at a repairman as he explains his work. Think of the system as a single loop with five separate components: refrigerant, compressor, condenser, evaporator and ductwork.

The compressor squeezes liquid refrigerant into a hot gas that flows to the condenser, where it changes back to liquid under high pressure and cycles into the evaporator coils at a much lower temperature. Filtered air cooled and dehumidified at the evaporator is then blown through ducts in the house, while the now warm refrigerant cycles back to the compressor for the process to repeat itself.

In a standard, split central air-conditioning system, the parts that accomplish all this are installed indoors and out. The condensing unit sitting outside on a concrete pad contains the compressor, condenser coils and a fan. Refrigerant-filled tubing runs from that unit to the indoor parts. Those include an evaporator coil housed in a “plenum,” which is basically a box, plus a condensate tray for catching moisture and a condensate drain pipe for carrying away excess water from the tray. The typical HVAC system also has blower and furnace components in a metal cabinet.

Throughout the house, of course, in the attic or under floors, lies the ductwork that ferries treated air from the system and then through a filter and back into it.

Controlling the whole system is the homeowner’s primary contact with its workings — that little thermostat on a wall.

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