Remount thermostat next to the water heater or in the sun. At least make sure all vents are pointed directly away from the thermostat.
Although afaik there is not outside air getting in. Just interior air is recirculated. people, cooking, bathing do add to the humidity. And when it is hot mine never cycles off anyway. Especially if the set point is very low.
The sensor in the intake is a freeze sensor and will only defeat your plan if disconnected. In fact you should make sure it is mounted up directly on or in the evaporator for best function. If your evaporator freezes you will not have cooling or humidity control. Maybe this is partly your issue.
Also check the inside plenum divider is well sealed between air in and air out. Remove all the interior trim to check this and the freeze sensor.
