E.S.
Definitely shut it off. The HVAC people won't be able to do anything until it's thawed out and the only way to do that is to shut it off. One time when that happened to us, we simply needed to change the filter. Another time when that happened, we ended up getting a new a/c unit. Could be anything! But first step is to shut if off. Hoping it's a quick (an inexpensive!) fix for you! Good luck.