It might be a good time to check your AC

Understanding your AC System

Don’t wait for a hot summer day to find out that your air conditioning is not working, when you may have to wait days for a service person. Here is a quick pre-season checklist, so that you can be sure that your AC is good to go. This video and article also explains in simple terms how your AC system works, and what can typically go wrong:

How your AC System works

The fundamental purpose of your AC system is to move heat from inside your house to the outside. To do this, your AC system has five essential parts:

  1. a heat exchanger outside of your house (the box on the outside of your house with the big fan in it, which is called the “condenser”);

  2. a heat exchanger inside of your house (the box inside your house with a blower which circulates the air from the inside of your house, which is called the “evaporator”);

  3. refrigerant piping (containing a special high-pressure fluid that absorbs and releases heat).

  4. ductwork which delivers cool air to your rooms, and draws warm air back.

  5. and, a thermostat that tells your system when to turn on and off.

Other components of your AC system include: the compressor (which is located in the outside unit) which circulates the refrigerant around; your air filter (which takes dust and particles out of the air which circulates through your house); and the condensate pump (which removes the water that drips from the inside unit).

A simple way to understand how your AC system works, is to think of the refrigerant in the pipes which go between your inside and outside units as a heat “conveyor belt.” Your inside heat exchanger puts heat onto the conveyor belt, and then your outside heat exchanger unit takes the heat off the conveyor belt. And this is how heat gets removed from your home. So even though you may think of your AC system as blowing “cold” air in your home, it is actually blowing air that has had its “heat removed”!

The other components of your AC system are there to make this process happen efficiently. For example, your compressor not only circulates the refrigerant around your system, but it also increases its pressure so that it can absorb and release heat more effectively. The blower circulates the air around your home. And your thermostat allows you to set your desired room temperature.

Some things that you may have noticed about your AC system is that if you are standing near your outside unit, that when it is running it will be blowing out hot air. This is the heat that is being removed from inside your house. If something obstructs the flow of air around this unit, then it can’t do its job of removing heat. So you will want to be sure that this unit is not cluttered with leaves or blocked by shrubs, etc.

And regarding your inside unit, you may have noticed a water condensation pump located next to the unit. The reason for this is that in the process of cooling the air, your air conditioner works as a dehumidifier. To understand this, imagine a cold glass of water on a hot day. In a little while, you will see water droplets forming on the outside of the glass. This is because when the warm air hits the cold glass, it causes water in the warm air to condense out. The same effect happens when the warm air in your home hits the cold refrigerant pipes in the inside unit of your air conditioner. And when the reservoir fills up with water, the condensate pump needs to kick on to pump it out of your home.


Now that we have discussed the different parts of your AC system and how they work, let’s now look at some things that typically go wrong with your AC system:


  1. Compressor: The motor in your compressor can go bad, or it can have valves that have problems. Or you can have leaks which develop around the compressor.

  2. Condenser: The fan for the condenser can develop problems, or the condenser coils can begin to leak.

  3. Refrigerant Lines: The refrigerant lines may begin to leak.

  4. Air filter: As your air filters get dirty, they reduce the energy efficiency of your AC system.

  5. Evaporator: The evaporator coils can start to leak.

  6. Condensate drain: The drain can become blocked, and if the system uses a pump, the pump can fail.

  7. Power to the system: From time to time, at peak loads, an AC system can sometimes trip its circuit breaker switch.



To prevent surprises when the temperatures start to soar, it is important to do a pre-season check of your AC system. Skipping this checklist could leave you sweltering on the first hot day of the year, when getting a service person to come out is more difficult and can be more expensive.

So here is a quick pre-season checklist for your AC system:

  1. Uncover the outside condenser unit.  (If you have covered it for the winter).

  2. Check the outside condenser unit.  Make sure that it is not obstructed by leaves, trash, etc. Also ensure that shrubs, etc are not blocking the condenser.

  3. Change your system’s air filters.

  4. Check air distribution registers in your rooms to be sure they are open (if you closed them for the winter). Also make sure that the registers are not blocked by furniture, carpeting or drapes.

  5. Inside unit:  Check the condensate drain pipes and drain pan. Sometimes the pan gets bumped out of place. Be sure that the pan is not cracked and the pipe is unobstructed. If you have a condensate pump, then pour some water in it to be sure the pump automatically kicks on.

  6. Switch on your AC to test it. You don’t have to run it for long, just check that it turns on and starts delivering cold air.

And if you are more ambitious and handy around the house, here are some other maintenance tasks which you should consider for your AC system:


Check condenser coils. Dirty condenser coil will cause the AC unit to be inefficient.  A dirty condenser coil will act as an insulator and prevent the rate of heat transfer.  Clean and straighten any bent fins of the unit.  And check condenser fan and oil the motor if necessary.


Clean the evaporator coils. If the coil is dirty it reduces its effectiveness for absorbing heat.  Clean the indoor blowers. In older models, the blower may have a fan belt that should be checked for tears and wear. If the blower has blades then clean the blades, as dirt on the blades can cause resistance to airflow. 


Inspect your exposed HVAC ductwork in unfinished areas to see if there are any air leaks.  Ductwork cleaning. You may be able to clean inside of your registers (both supply and delivery registers) with a vacuum attachment, however, a more thorough cleaning of your entire system will require a professional.


We hope that the article has helped you understand the parts of your central AC system, how they work, what typically may go wrong, and how to do pre-season maintenance for your system.

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