Turn The Unit On & Make Sure It Kicks In And Runs Properly

Start at the unit control or thermostat. Turn the unit on and make sure it kicks in and runs properly. If the unit doesn’t run, call a technician. Because this inside air always has some amount of moisture suspended in it, the cooling portion of the process always causes ambient warm water vapor to condense on the cooling coils and to drip from them down onto a catch tray at the bottom of the unit from which it must then be routed outside, usually through a drain hole.

As this moisture has no dissolved minerals in it, it never causes mineral buildup on the coils, though if the unit is set at its strongest cooling setting and happens to have inadequate circulation of air through the coils and also experiences a failure of the thermistor which senses the ambient temperature in the room, the coil’s fins can develop a layer of ice which will then grow and eventually block the circulation of air on the cool side of the unit altogether in a positive feedback loop that will cause the formation of an ice block inside the unit: only minuscule amounts of cool air will then manage to come from the exhaust vent until this ice is removed or is allowed to melt.

This will happen even if the ambient humidity level is low: once ice begins to form on the evaporative fins, it will reduce circulation efficiency and cause the development of more ice, etc.

A clean and strong circulatory fan can help prevent this, as will raising the target cool temperature of the unit’s thermostat to a point that the compressor is allowed to turn off occasionally.

A failing thermistor may also cause this problem. This is the same issue faced by refrigerators that do not have a defrost cycle. Dust can also cause the fins to begin blocking air flow with the same undesirable result: ice.

By running an air conditioner’s compressor in the opposite direction, the overall effect can be completely reversed and the indoor compartment will become heated instead of cooled. See heat pump. The engineering of physical and thermodynamic properties of gas–vapor mixtures is called psychrometrics.