The air handler is the interior portion of your central air conditioner's split system, completed by the condensing unit outside. Typically located within the furnace, the air handler contains an inlet valve, evaporator coils, a drip pan, and a blower fan that all work in conjunction to ensure the refrigerant fuel entering the system provides your home with cooled air.
The blower fan provides the vital role of blowing warm air across the cooled evaporator coils, then pushing that air out into your home. While the fan can malfunction due to loosened blades or a dead motor, other parts of the air handler can also impair the functionality of the blower fan.
Malfunctioning Inlet Valve Doesn't Allow Coils to Cool
The inlet valve in the air handler makes sure that the liquid refrigerant coming in from outside doesn't enter the coils too fast, which can cause a dangerous backflow or a loss in cooling efficiency, as the coils can't handle phase change on that much liquid at one time. If the valve becomes partly or fully stuck closed, the coils won't receive the amount of refrigerant necessary to make a phase change.
If the coils don't become cold, the blower fan will still do its job of circulating the air, but the air coming back out of your vents will feel warm. Turning down the thermostat won't do any good. You can check the coils to make sure the surface isn't dirty, as that can also cause the coils to fail to cool. Clean dirty coils with a no-rinse foaming cleanser to see if that helps.
If your unit continues to blow out warm air after the coils are cleaned, call an HVAC contractor service like Hartman Heating, Air and Fireplaces for diagnostics to see if the valve is the problem and to replace the part, if necessary.
Frozen Coils Shutdown the Cooling Process
Evaporator coils can also become too cold due to a refrigerant imbalance due to a broken valve or a problem with the type or amount of refrigerant. Coils can freeze, which sounds like it would make for a fantastic cooling experience on a hot summer day. But the frozen coils won't continue to phase change the refrigerant passing through the system, which will cause problems in the condensing unit that can lead to a total system shutdown due to a safety sensor. When the system shuts down, the fan no longer blows across those frozen coils, and you lose the cold air.
If you have noticed your evaporator coils are continually freezing, there is likely a problem with the refrigerant. You can't fix refrigerant issues on your own since it is a controlled chemical in most areas. Call an HVAC tech to check on the chemical and its supply and to fix any problems, as needed.