drain freezes every 2 weeks

These are one of the toughest drains to stop from freezing over. A few things that have worked for me in the past is adjusting the front leveling legs so that there is a slight tilt to the rear to help the water flow down the drain line. The other thing that you could try which is not likely recommended by the manufacturer but installing a defrost termination that is 5 degrees higher than the OEM termination that is currently installed. It Is usually clipped to the evaporator towards the front of the unit. If you remove the termination you will see the rating on the side usually they will say something like 30/55 which means it closes at 30 degrees and opens at 55 degrees. By installing a termination the closes at 60 degrees it will allow the heater to stay on just a little longer to help the rest of the dripping water from the defrost cycle to pass through the drain before the cooling begins again. Hope this helps.