Why is my air-conditioner icing up?

By Ian Stringer The most common cause for your air-conditioner to "ice-up" is poor airflow. As an HVAC technician the first thing I check when called to check an air-conditioner that doesn't seem to be cooling is the air filter.
Yes there are filters in your air-handler or furnace. This is the number one cause of poor cooling. Air filters should be checked every month to ensure proper operation of your A/C.
Below are pictures of an iced up A/C and a diagram explaining the refrigerant cycle of a residential split air-conditioner.
If the refrigerant cannot extract the heat from the air inside the home (due to poor airflow across the evaporator) it wont take long until it freezes up.
If the air filter seems OK the next thing to check is the blower itself. Some older furnaces or air handlers have belt driven blower motors. If the belt is loose or broken there will not be sufficient airflow moving across the evaporator coil.
Next, if it seems that maintenance has been neglected and the filter (at present) looks good  then there is a good chance that the evaporator coil has become clogged.
If all these symptoms are not evident, its time to call a service guy.
At this point the cause is most likely an undercharge of refrigerant or a leak. Ensure that, if there is a leak, it gets repaired. In fact its illegal at least in Canada to add refrigerant to a system that has a leak. Just "topping up" the system is a band-aid, if not repaired it will leak again.

By Advanced HVAC Systems