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How to Clean an AC Condenser (Outdoor Unit) Safely

Shut off power at the disconnect, clear debris, rinse the coil from the inside out with low-pressure water, straighten bent fins and keep the unit clear. What to leave to a technician.

By Kadir Özbek · Updated · 2 sources

Short answer

Turn off the thermostat and pull the outdoor disconnect, clear leaves and debris from around and inside the unit, then rinse the coil gently with a garden hose from the inside out if you can reach it, or from the outside in at low pressure. Never use a pressure washer, and leave refrigerant and electrical parts to a technician.

Difficulty
Easy
Time
45–90 minutes
Typical cost
$0–$25 (optional coil cleaner and fin comb)
On this page · 12 sections
  1. When to clean it
  2. Step 1: Shut off power
  3. Step 2: Clear the area
  4. Step 3: Clean inside the cabinet
  5. Step 4: Rinse the coil
  6. Step 5: Straighten bent fins
  7. Step 6: Reassemble and restore power
  8. Check the results
  9. What not to do
  10. Common mistakes
  11. When to call a technician
  12. Sources

Before you start

  • Garden hose with adjustable spray nozzle
  • Soft brush or shop vacuum with brush attachment
  • Screwdriver or nut driver (to remove the top grille)
  • Fin comb (optional)
  • Work gloves
  • Coil cleaner labeled for AC condensers (optional)

The outdoor unit of a central air conditioner or heat pump has one job: release the heat pulled out of your house. It does that by blowing outdoor air across a large coil. When grass clippings, leaves, cottonwood fluff, pet hair and dirt mat the coil’s fins, that air cannot pass through, and the system runs longer to cool less. ENERGY STAR notes that dirty coils reduce a system’s ability to cool, make it run longer, increase energy costs and reduce equipment life.

When to clean it

  • Once each spring before cooling season, and again mid-summer if you live near cottonwoods, lawns that are mowed often, or construction.
  • Whenever you see debris packed against the coil fins.
  • When the system runs constantly on mild days and the air is not as cold as it used to be.

Step 1: Shut off power

  1. Turn the thermostat to OFF.
  2. Find the disconnect box mounted on the wall near the outdoor unit. Pull out the disconnect block or switch it to OFF.
  3. For extra safety, also switch off the double breaker for the outdoor unit in the main panel.

The unit contains high voltage and a capacitor that can hold a charge. Do not open the electrical access panel.

Step 2: Clear the area

Remove leaves, sticks and debris from around the base. Trim shrubs and grass so there is clear space around the unit on all sides and above it, following the clearance in your unit’s manual. Clear the top grille and fan area.

Step 3: Clean inside the cabinet

On many units, the top grille with the fan attached can be unscrewed and lifted. Support it carefully so the fan’s wires are not strained, or have a helper hold it. Reach in and remove debris that has fallen inside. If the top is difficult to lift or wiring is tight, skip this step and clean from the outside only.

Step 4: Rinse the coil

  1. Set the hose nozzle to a gentle shower, not a jet. Never use a pressure washer; it flattens the soft aluminum fins.
  2. If the top is off, spray from the inside of the cabinet outward, which pushes debris out the way it came in.
  3. If the top is on, spray from the outside straight in, at low pressure and straight along the fins rather than at an angle.
  4. For greasy or stubborn dirt, apply a coil cleaner labeled for condenser coils, following its directions, then rinse.

Brushing the outside of the fins lightly with a soft brush before rinsing removes surface fluff.

Step 5: Straighten bent fins

Bent fins block airflow. A fin comb slides along the fins to straighten them. Work gently; aggressive straightening can tear fins or nick the tubes underneath.

Step 6: Reassemble and restore power

Replace the top grille, make sure the fan spins freely by hand, reinstall the disconnect and turn the breaker back on. Wait a few minutes, then set the thermostat to COOL and check that the outdoor fan runs.

Check the results

After cleaning, let the system run for 15 to 20 minutes on a warm day. Hold your hand above the top grille: the air coming out should feel noticeably warm, which means the coil is shedding heat. Inside, compare the air at a supply register with the air at a return. If the outdoor air is barely warm and the indoor air is not much cooler than before, the problem is not dirt alone, and a refrigerant or component issue is likely.

What not to do

  • Do not bend or loosen refrigerant lines or fittings.
  • Do not open the electrical compartment.
  • Do not cover the unit during the cooling season.
  • Do not wrap the unit in plastic for winter if it is a heat pump, which runs all year.

Common mistakes

  • Cleaning without pulling the disconnect.
  • Using a pressure washer.
  • Letting the fan hang by its wires with the top removed.
  • Planting shrubs right against the unit.

When to call a technician

Call an HVAC technician if the coil is heavily corroded, if fins are badly crushed over large areas, if the fan does not spin or hums without turning, if you see oily spots on the coil or lines (a possible refrigerant leak), or if cooling does not improve after cleaning. ENERGY STAR’s checklist recommends an annual spring check-up that includes cleaning both evaporator and condenser coils and checking refrigerant level. Refrigerant work requires EPA Section 608 certification.

Sources

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