Dehumidifier freezing and failing to

I have a model M7DH65B2A that had the same problem.  The metal clip that holds the frost sensor to the evaporator coil had rusted clear through and the sensor was hanging in midair.  Not knowing whether I could get a replacement, I re-attached the sensor securely to 2 of the loops of the coil with nylon ties and a bit of thermal heat sink compound, available at many electronics specialty stores.  Problem solved.  You may want to get the correct parts to repair your unit, but I chose to go this route because my repair will never rust through.

It will be difficult but let me explain how to arrive at a point of investigating.
Note where and how far the frost starts to go by noting on the cold coil where the frost is and how long it takes to develop. IF it starts only after several minutes and progresses to cover the face all at once (or steady and within Id say within 1 hour the whole face) its most likely fully charged and the control is weak or bad or it could be operating in too cold of an environment to dehumidify correctly, usually the temp has to be 80'F or more for the dehumidify to work without freezing.
Also Low air flow from the circularity fan can cause the face to freeze up in this manner so run it on high speed if the temp is low to keep warmer air pulling over the coil. If your in proximity to the blower it will be cold but you have to decide on cool and damp or cold and dry.

If the temp is above this 80'F and the face freezes up and usually starts to freeze up on the refrigerant inlet end of the coil and slowly moves across the face to the other side and progresses back and forth til the whole face is covered it is most likely low charge. This can also be noted by thicker frost or ice closer to one end or maybe the bottom than at the top. and often it will not cover the whole face for a few hours.

The humidity switch (Hydrometer sensor) may be at fault or compressor or fan is not running.First You could go directly to the compressor and make sure it is or is not getting power first. If the compressor has power then the compressor is suspect (sometimes when 1 wont start it gets hot to the touch) In any case the fan(s) should run with it on and trying to dehumidify. Look at my tips and tricks for compressor check out if it has power and dosn't run..

2 KINDS of CONTROLS for your DEHUMIDIFY
If it has an electronic display the sensor will be a small probe close to the inlet of the air inlet circulation. Maybe its not in place.This type control is not something that can usually be checked without an ohm meter, thermometer, and Hydrometer or Psychometric measuring device to arrive at the wet-dry bulb temperatures thus determining the humidity and charts to determine the resistance value of the sensor(s). So replace the board and sensor on this type.

As for the drain most have a plastic pan and this is sometimes the type that has to be removed and dumped or a hose has to be attached and the hole it attaches to has to be cut out for self draining.