I forgot to mention, many units have a selectable timer for how often the unit goes into defrost mode. It might just need to be set for a longer time interval. The ones I've seen have a jumper wire on the circuit board to select the timer.
You would need to dig out the installation manuals or have a tech check it, if you are not comfortable.
You would need to dig out the installation manuals or have a tech check it, if you are not comfortable.