When coming home after a long day out on a stuffy summer’s afternoon, the last thing you want to be greeted with upon walking through the front door is a blast of warm air. If you discover that your air conditioner has stopped blowing cold air, you’ll probably wonder what to do for the fastest fix.

How Heating and Cooling Systems-work

Before investigating your AC's troubles, you should have a basic understanding of how it functions. For an in-depth look at residential HVAC systems, check out how heating and cooling systems work.

Air Conditioning 101

All residential air conditioning systems, whether operating as a split system or a heat pump, utilize the same basic method to cool your home. Essentially, your air conditioner pulls in warm air from inside the home, extracts heat from it, and circulates the now-cool air through your duct system and into the different rooms of your home. This is accomplished by the two major components of an air conditioning system: the condenser (the unit that sits outside your home) and the evaporator. When your air conditioner is blowing warm air, there’s a good chance that your condenser is simply dirty.

How to Clean Your Condenser in 7 Steps:

  1. Shut down all power to the unit. Attached to the condenser should be a metal box that houses the disconnect switch. This is where you’ll turn off the 240 volts that power the condenser. The way to do this will vary depending on the particular system, so consult your system’s manual or call the installer before beginning. Generally, the power can be shut down by pulling a shutdown handle, removing a fuse, or disconnecting a power cord. Also make sure to turn off the circuit at your main electrical panel.

  2. After waiting a few minutes to ensure that all the remaining charge is gone, unscrew and remove the top panel or grille as well as any protective side grilles. Be careful with this step, as sometimes the unit’s fan is attached to the top panel or grille. If this is the case, make sure you don’t disturb any wires connected to the fan.

  3. Clean Condenser Coils

    When you remove the protective grilles, you’ll notice that the condenser coils are surrounded by flat panels, or fins, usually made out of aluminum. With a soft brush, clean the fins and coils of any debris or dust, taking care not to bend the fins, and remove any loose debris from the bottom of the unit. Then, if possible, use a bristle attachment to vacuum away any remaining dirt or dust.

  4. Next, cover the wiring and the motor with a plastic bag (a garbage bag would work nicely) and duct tape, and use a hose with a trigger nozzle to clean out the coils and fins. Do not use a high-pressure stream, as the aluminum fins can be easily bent by water pressure. After the water has drained from inside the bottom of the unit, remove the plastic covering.

  5. Fin Comb and Professional HVAC Contractor

    If any of the fins are bent, you’ll want to have them straightened for optimal performance. This requires a special tool called a fin comb and is best left to a professional HVAC contractor. Make a note to call one to repair your unit before the heavy-use season begins. Tips for choosing a contractor.

  6. Screw the protective grilles back onto the unit. After you’ve finished cleaning the condenser, use a level to make sure that the unit is balanced properly. If the unit isn’t level, drainage problems may occur.

  7. Finally, turn the thermostat off before reconnecting the power to the unit. After the thermostat is turned off, reengage the power to the unit at the main service panel and the disconnect box, and then set the thermostat to cool. After a few minutes, locate the two pipes connecting the outdoor unit to the indoor air handler. One of the pipes should be cool, and the other should be warm.

Refrigerant Recharged and Professional HVAC Contractor

If cleaning the condenser unit doesn't solve your problem, then you likely need to have your refrigerant recharged. This is something best left to a professional: read local reviews.

Smart maintenance: Even if your AC is working fine, cleaning your condenser is something that should be done every year, ideally on a warm day before the heavy-use season. As you can imagine, the HVAC business is highly cyclical, so you want to avoid having to call for AC repair during the busy summer months. If you give your system a good cleaning in the spring, you can hopefully catch any small problems (such as bent condenser fins) before they bring your whole system down just when you need it the most. More about HVAC maintenance.

If you end up needing to replace it, know how to choose the right HVAC system.

View Local Air Conditioning and Heating Companies

Sources: About.com; HomeTips; HowStuffWorks.