We’ve already had a few days of hot weather and in no time you will want to start using your central air conditioner, the largest electricity load of a typical house.  The air conditioners compressor and condensing coil is located in the unit you see outside of your home.

Before you consider using your air conditioner make sure you:


Take off the winter cover

It may sound obvious to take off the winter cover but it happens all of the time. You want to be sure you’ve removed the cover before the temperature heats up and the air conditioner comes on.  If the air conditioner comes on when the cover is still on, you could permanently damage the unit and suddenly need a new air conditioner ($2000 – $4000).  It is recommended that you do not turn on the air conditioner unless the outside temperature is above 16° C because the liquid being pumped by the compressor will be heavy and you may severely damage the heart of the system, the compressor. If the compressor is damaged it will need replacement.

Clean up around the unit

Cut back any trees, shrubs, plants that are near the unit that have grown since last year.  I would recommend 12” – 24” of clearance all around.  Brush away any leaves or large debris that is on the outside of the unit.

Make sure your unit is level

Some air conditioning units are sitting on a cement block on the ground and these will settle and become un-level over time.  As little as a 10°tilt can affect the operation of your unit. The high speed fan bearings could wear out prematurely and the refrigerant or compressor copper lines can become damaged.

If you are replacing your unit I recommend installing a metal bracket fastened to the foundation (see photo) to ensure the unit stays perfectly level and it helps avoid debris and dirt from the ground.

Bracket Supporting Compressor Outside

Bracket Supporting Compressor Outside

Blow out the dust and dirt

To help the efficiency of your air condition it is a good idea to blow out dust and dirt from between the fins of the condensing coil fins outside.  The dirt impedes the heat transfer that needs to happen at the tiny spaces between the fins and will make the air conditioner work longer to achieve its job of cooling the house.  Working longer means using more electricity, costing more money and increasing the environmental impact so it is in everyone’s interest to keep the fins clean outside. 

Full view of outside unit

Outside Compressor and Fins

Use an air compressor or pressure washer to clean out between the fins.  Be careful not to bend the thin fins by getting too close to them with air hose or pressure washer.  That is why those metal grates are there, to protect the fins.

Exterior Air Conditioner close up look

Close up look at Fins

The same applies inside the house.  There are fins in a coil unit (evaporator coil) inside the duct (plenum) of the furnace.  The cold liquid runs through the small pipe and the fins attached to the pipe cool the air when the air passes between them. That air continues on through the ducts to cool the house. (Figure from www.alpinehomeair.com).  See how narrow the spaces are in the figure below.

AC evaporator coil inside furnace plenum from alpinehomeair.com

Evaporator Coil inside ducting in house

These fins need to be kept clean for efficiency, cost and environment reasons as stated for outside unit.  To help keep this clean you must ensure your furnace filter is cleaned/replaced about every two months or as recommended by filter manufacturer if you have a thick box shape filter.

Standard Furnace Filter

Standard Air Filter size and location


Thicker furnace filter

Thicker Furnace Filter

Clean or replace your furnace filter

When replacing the furnace filter, make sure you turn off the furnace first.  Nobody ever talks about this but think about it.  If you have a dirty filter and the furnace distribution fan is running and air is moving then you slide out the filter, any dirt, hair, dust bunnies … that is behind the filter will be blown through the opening while you are fumbling to get the new filter in the slot.  The air movement makes the filter stick and difficult to move as well, so just turn off the furnace for a minute while you change it.   


Even if you keep the filter clean and replaced regularly dust and dirt will accumulate on the cold condensation on the metal fins on the evaporator coil in the plenum ducting.  It is a good practice to have the furnace and air conditioner evaporator coil  cleaned professionally every 2 years along with all the ducts in the house.  Cleaning of the inside evaporator coil by the furnace in the ducting should be done by a professional company who is experienced cleaning out units.  I do not recommend it as a DIY job.

When your air conditioner runs efficiently you will save money on your electrical bill as well ensure your air conditioner meets or exceeds the expected life (12 – 15 years).

If you have any questions or comments contact me.

Brad Durant, P.Eng., RHI –  25+years as a professional Civil Engineer and 12+ years as Owner of Home Front Professional Home Inspections

“Educating People one at a Time”