I noticed last night that the temperature coming out of our vents was colder than normal. I checked the A/C unit and upon inspecting it noted about 1/16-1/32 inch of ice covering the pipe going from the compressor into the evaporator coils.
The ice defrosted in about 30 seconds after having shut off the unit (it had been on about 30 minutes prior).
This morning I started unit and it formed frost in about 3 minutes. I checked the airflow, removed the filter and it still formed. The evaporator coils underside is pretty dirty, but I noticed that when I shut off the A/C this morning the last place the frost melted was the large hex nut that attaches the pipe to the compressor. I have someone coming out to inspect the unit in a few days, but I was hoping you all could shed light on either how to clean the evaporator coils if that indeed could be the problem or how long I can run the system at a time and not freeze it up given temperatures in the mid 80s during the day and 60s at night before someone comes and inspects the system for a leak/low freon.
Also if thee is indeed a leak that is the problem, the unit was made in 1999. Was R-22 used in units then, or was it another type of refridgerant?
Thanks for your help