You may only need a defrost sensor. Unfortunately the issue you are having can also be caused by low refrigerant and or a bad board. If your unit has a TXV valve that has stopped working properly you could develop this issue aswell. Make sure the fan is operating normally and your evap coil is clean. I would start with the sensor first and if it turns out to be good then call an HVAC pro, otherwise you could spend a lot of money trying to fix the wrong problem.
Answers & Comments
You may only need a defrost sensor. Unfortunately the issue you are having can also be caused by low refrigerant and or a bad board. If your unit has a TXV valve that has stopped working properly you could develop this issue aswell. Make sure the fan is operating normally and your evap coil is clean. I would start with the sensor first and if it turns out to be good then call an HVAC pro, otherwise you could spend a lot of money trying to fix the wrong problem.