How to Clean AC Evaporator Coils

Photo tutorial showing how to clean AC evaporator coils with no-rinse spray foam cleaner.

If you’re not comfortable cleaning the AC evaporator coils yourself, at least you’ll what’s needed when calling a Heating, Ventilation and Air Conditioning (HVAC) professional.

Central Air Conditioner Routine Maintenance

Routine inspection and maintenance is very important to catch problems early and save on your electric bill. I recommend hiring an HVAC technician to inspect and maintain the AC system twice a year; Spring and Fall are best before the summer or winter season begins and you really need your system.

The most important thing a home owner should do is regularly change the air filter every month. I installed Honeywell touchscreen 7-day programmable digital thermostats that reminds me when it’s time to change the air filter. A dirty air filter will increase your electric bill as the system struggles to heat or cool your home.

Other things a careful and knowledgeable homeowner can do is clean the evaporator coils.

AC Air Handler Components

The following photo is the central air handler in my attic. It is known as an “upflow” type because air enters from the bottom and exits out the top. The unit combines a natural gas furnace and an air conditioning evaporator coil. It has three major sections:

  1. Blower motor – bottom
  2. Gas furnace – center
  3. A/C evaporator coil – top

The entire air handler sits on a secondary drain pan with a cutoff float switch. The purpose of the secondary drain pan is catch water in case the condensate drain line becomes clogged or the main condensate pan rusts through. The secondary pan will catch the water and eventually activate the float switch to shut down the entire unit before it overflows and ruins the ceiling. Too often, the secondary drain pan becomes rusty and fails to hold the water.

AC Evaporator Coil Cleaning: Air Handler Components

The blower motor forces air upward (recall my air handler is an “updraft” or “upflow” type) through the furnace and air conditioner evaporator coils. The Heat and Cool functions of the thermostat ensure that either the furnace or the air conditioner operate, but never both at the same time. The supply air plenum box sits on evaporator coil sheet metal cabinet. Two large flexible ducts are connected the plenum box. The large trunk flex ducts connect to rigid duct board distribution trunk ducts that lay on the attic joists. Several smaller flexible duct branch lines are taken off the rigid trunk duct to supply air to vents throughout the house.

HVAC Air Handler Evaporator Coil Cabinet, Plenum and Flexible Ducts

How to Clean AC Evaporator Coils

Before you begin, turn off the air conditioner at the thermostat and shutoff the electricity to the air handler. There should be a toggle switch (it will look like a light switch) by the air handler to turn off the power. If not then shutoff the electricity at the circuit breaker panel.

The evaporator coil access panel must be removed to access the coils. This is a closeup of the evaporator coil access panel, which is fastened with nine 1/4 inch sheet metal screws and sealed along the bottom with metal foil HVAC tape.

Evaporator Coil Cleaning: Evaporator Coil Case and Access Panel

Remove the access panel screws with a socket wrench and peel away the metal foil tape along the panel edges (if any).

Remove the Evaporator Coil Access Panel

The access panel is removed exposing the AC evaporator coils in the following photo. The evaporator coils are basically a heat exchanger, cooling the air inside the house and transferring the heat to the outside condenser unit.

AC Evaporator Coil Cleaning: Access Panel

A-Frame AC Evaporator Coil

My AC unit has what’s known as an A-frame style evaporator coil. The coil has a two halves joined together like the letter A and sits on a condensate drip pan. The drip pan forms a moat under the coils to catch the water dripping down as warm humid air from the house is chilled as it moves across the cold coils. The bottom of the A-frame is open so the air can flow through.

A-Frame Evaporator Coil

The better evaporator coils have a plastic condensate pan to that won’t rust through. If the condensate pan were to develop a leak – or the condensate drain were to get clogged up, the water will do one of two things:

  1. Overflow and pool in the safety condensate pan under the whole unit, which will eventually fill up and trip the safety float switch, shutting down the unit. The purpose of the float switch is to prevent the pan from overflowing and causing water damage to the ceiling and rooms below.
  2. If the unit doesn’t have a safety pan under the unit, you’ll have water damage right away.

On a typical summer day, the evaporator coils can generate gallons of condensate water as it dries and cools the air inside the home.