"Limited or No Cool Air Coming From Air Vents"

 By Ron Stultz

28 June 2010

Summary: if your outside compressor unit is running (not just the fan motor on top), in all likelihood, your system needs a "Freon" charge. Adding "Freon" is not a do it yourself (DIY) task so call a HVAC service man. If your system has had to be charged several times in a relatively short period, such as in a year, there is probably a leak somewhere the HVAC service man needs to find.

Background:

Home HVAC systems use "Freon".

Freon fluid has the property that when it is compressed, it gives off heat.

Freon fluid has the property that when it is allowed to expand from a pressurized state, it absorbs heat.

A HVAC system works by compressing "Freon" at the outside compressor unit and routing high pressure "Freon" around coils that are cooled by the fan located on the top of the compressor unit.

From the compressor unit, once as much heat as possible is removed, "Freon" is piped to the air handler, blower, inside the house, where the pressure of the "Freon" is reduced in coils inside the air handler. As air is blown over the pressure reducing coils, the "Freon" picks up heat from the air, cooling it.

What goes wrong:

With little or no cool air coming from air vents, the first thing to do is check to see if the outside compressor unit is running.

If either the fan on top of the outside unit is not running and or the compressor unit is not running, the problem is probably with either a blown fan or bad run capacitor. See "HVAC - Outside Compressor or Fan Not Starting or Running"

If the compressor and fan are running, your system probably needs a charge of Freon.

Freon

"Freon" is funny.

For a HVAC system to work correctly, it must have the correct amount of Freon in the system.

If some Freon leaks out of the system, when the Freon is allowed to expand in the cooling coils of the inside air handler, the Freon will get so cold, moisture in the air being blown across the coils will condense out and eventually freeze on the coils, blocking air flow.

If you are a mind to, you can go to your air handler and open it up to see the coiling coils. If they are frozen solid, time for the Freon to be checked.