How did my Air Conditioner Freeze Up

When a persons Air conditioner freezes up they have a hard time figuring out why, well here are some low tech explanations that I think will make sense to you.
When your air conditioner runs it has a pupose and this purpose is to take the heat out of your house the way it does that is to transfer that heat energy into another substance besides your air, for the purpose of this explanation we will use refrigerant more commonly known by the dupont brand name Freon.
In order for energy to transfer you need to have a temperature difference and when you supply that temperature difference the energy will move from the hot substance to the cooler substance until both are the same temperature. When you put an ice cube in your hand your hand gets cold right? What happens to the poor ice cube, it picks up heat until it can't absorb anymore then you have a wet hand right.
To trasfer the heat energy out of the air in your house we usually use the refrigerant flowing through a series of copper coils pressed together with aluminum fins called an evaporator or indoor coil. With the refrigerant at the right pressure in this coil the corresponding temperature will typically be 38-45 degrees, so that when you draw your 75-80 degree air across it you will pick up heat as we discussed earlier. Because that coil temperature is below what is called the dew point of the air in your house in addition to giving up heat the air will also relieve itself of moisture or precipitate. This moisture travels down the coil to the drain and everything works as it should. When a freeze up occurs a couple of things happen that aren't supposed to.

1. your coil temperature gets below freezing

2. the water that is precipitating out of your air is not water anymore it's ice

There could be a couple of explanations for this
1. The most common reason for a freeze up is your filter is dirty (and you will feel so foolish if you call a service person out to your home and he pulls the dirty filter out and charges you $100 so don't let this happen to you). Your air conditioner is designed for a certain amount of airflow and anything less than that will cause the coil temperature to drop because you air not drawing enough warm air across it to give the refrigerant heat to pick up.

2.The second reason your coil might freeze up is low refrigerant pressure jusst like low airflow not providing enough heat for the system low refrigerant pressure does not provide enough transfer media (refrigerant) for the system the coil temperature drops in the first part of the coil while it rises in the rest of it, but that cold part starts ice and works its way up the coil over time.

These are not the only reasons just the most common. Low airflow may be caused by duct obstructions, a bad fan motor,a coil that is very dirty or too many of the supply grilles closed.
Low refrigerant pressure is caused by leaks or obstructions in the system.

If you want to save money the next time you have a freeze up check these things out.