My air conditioner will start to cool, but after a short time it stops cooling, I have found that the unit forms frost on the incoming tubing. I have turned the unit off and let it thaw out and make sure it is dry. When I turn it back on, it does the same thing again, What may be the problem?

Lack of air flow (dirty filter,filter installed backwards,dirty evaporator coil,dirty condensing coil) low on refrigerant (leak in system), Or fan motor (blower or condensing going out on its internal overload).These are the things to check