Thanks for the responses. Last winter during an ice storm it had a couple inches of ice on the top, inside and outside of the unit. The HVAC company came out 4 times (replaced the sensor and circuit board) and finally said it was fixed. Seems like anytime it sleets or snows though it ices both on the inside and outside of the coils. I'll keep an eye on it to make sure it does ice up too much again. I replaced the thermostat last year so could that have affected anything?
Thanks for the tip on turning on the AC. I'll have to give that a try.
Here's a picture of the circuit board. I didn't see anything that says defrost