The control scheme you conjure will determine how effective your unit will operate. From your comments, fan speed is an issue. To wring high humidity out of the air takes lots of energy and low airflow. The newer units that have a dehumidification function basically run the air handler at the slowest possible speed while cycling the compressor on and off.
The idea is to force the evaporator to partially frost up. Once a relatively small amount of frost forms, it begins to choke the airflow through the hx. What air makes it through the evaporator is cold and dry.The longer the compressor runs, the more frost forms.
After a short time, the compressor shuts off and the low flow of air melts the frost as it is wrung of moisture. The cold evaporator continues to draw moisture from the circulated air as it warms its way to the dew point. After some time has elapsed, the compressor starts back up, and the cycle repeats. The evaporator is charged and discharged like a thermal capacitor or battery to dehumidify the air without removing too much heat too fast.
If it were mine, I would be tempted to find a portable dehumidification unit with a leak or burnt out compressor and rob its guts. The defrost thermometer and relay outputs could be easily rigged to what you have and assume limited control pretty darn simple. If you don't want to do anything custom, a duty cycle timer could toggle between "fan only" mode and cooling stage 1 if the fan speed could be slowed.
|