Air Conditioning - frozen ac lines

the lines running from my ac unit inside have frost on them. the unit is running but not cool air coming out of vents - - i've turned the unit off at the wall and in the attic.

will that assist in unthawing the lines or do i need a hvac specialist on site to do more?

You were right in turning the unit off when you saw the frost and lack of cooling. Prolonged running while frozen is not good for your unit.

Your evaporator coil inside/A-coil froze up, and that is why your cooling stopped.

You can turn on only your blower on your air handler to help melt the ice.

Before you call a tech, there is something you can do - check your air filter. A dirty air filter reduces air flow across your coil and can make it freeze up. If it is dirty, replace it, and once thawed try the unit again and watch for signs of freezing.

If your filter is fine/changing it doesn't help, call a tech. You may have low refrigerant (R-22/R-410a) and as you may or may not know you need EPA or other certification applicable to your jurisdication to work on the sealed side of the unit.

is there some degree of repair necessary to prevent the freezing of lines fm reoccurring?

If the air filter, fan, & indoor coil are clean and no registers are closed or otherwise blocked, the most likely cause of freezing is being low on refrigerant. Only two things will cause a freeze up: Lack of air flow & low on refrigerant. Checking the refrigerant MUST be done by a certified technician.

If everything else checks out (you DON'T find a plugged filter, or other blockage somewhere) and you call a tech who find low refrigerant, make sure the leak is found and repaired. Refrigerant doesn't disapear or need changing ever, it only goes due to a leak and refilling it would just be a sometimes very expensive temporary fix.