Air Conditioning Repair my coil is frezzing up

Refrigeration Problems
Some refrigeration problems can be due to lack of airflow, either from dirty filters or
dirty coils, as noted above. If the evaporator coil is freezing up, these are easy
preliminary checks to be made. Another cause of low airflow can be a belt / pulley
problem, if your equipment has this sort of motor / fan drive, as the belt may be slipping
and reducing the fan air output. This is easily fixed by tightening the belt, but you should
check your manual, as overtightening may reduce the life of the bearings.
However, the most common cause of freezing is probably a low refrigerant charge, as the
pressure of the refrigerant in the system determines the temperature, and a lower pressure
corresponds to a lower temperature. Over the years you may expect that some refrigerant
is lost through joints and fittings, particularly with an older system. Also, most
equipment is designed to be used in hot weather. If the outside temperature is not high,
say below 65ºF, but your system is still needing cooling because of high internal heat
loads, you may find that you get freezing, and this is a result of the equipment
manufacturer’s decisions for design of the unit.