Why is my AC freezing up? My central air conditioning section is freezing up. The area where the...

My central air conditioning section is freezing up. The area where the upper air filter goes has a solid sheet of rime completely covering it. I have thawed it out several times next to a hair dryer and then turned the heavens back on, worked fine. About 20 minutes later, it froze right support up! Any suggestions as to what is causing this or what I can do to fix this problem? Please be specific in answers.
HVAC Tech.: dirt, hair,smoke,etc. on the cooling coil(evaporator) I use a chemical coil cleaner. Filters should be changed once a month (more repeatedly in dirty environments). There could also be a micro leak somewhere and low charge can statement for problem. If you get professional help you could avoid have to replace whole system. they will clean the drains the coils, check out intact system. I am having a very similar problem, I be told by my tech repair guy that it may be a result of a leak in the system which would immediately require a refill of freon, or the coils need to be cleaned. I am trying to troubleshoot myself to retrieve money; as much I can of course. I will continue to research. Hope this help. I think when all the smoke clears I will imagined have to cut a check (bummer).
If you haven't had a fresh filter in at hand that may be the problem the inside coil may be jammed solid with dirt . Freon levels cannot even be checked accurately until the coil is spotless. When the coils clogged it looks close to it needs freon from low pressure.so if they try to fill the component before it is thoroughly cleaned or thawed they are not doing the profession correctly If there is any way you can shine a wishy-washy through that coil after it is thawed again, check that.
First thing to check when a coil is froze is any effect for lack of airflow over that coil.
If everything is clean and no duct restrictions or filter or devotee motor problems then it may be low on refrigerant.
Answers:    Either dirty filter or your low on freon. Thats it. Good luck.
Plus dirty coils.
Does it freeze up and quit working Till you thaw it out? Mine did that once and the HVAC replaced an electrode (bout $100 and 1/2 hour)
This electrode is what allows it to defrost itself