Dehumidifier Problem

Unplug unit. Empty the bucket and put a jumper across the sensor leads.

Plug in unit. See if it works.

Yeah we have done all of that with every possible devise in the thing. After some research I found out that jumping the sensor leads is not going to do anything as the sensor is a capacitor. The onboard computer measures the capacitors value as it changes by the humidity.

I believe the sensor is called a thermistor, and it is probably used as low temperature safety control...This circuit board is nothing more than an on/off switch, if you have a voltage meter just check the power coming in and see where it stops...ie. is it entering the circuit board? The humidistat control should be tied into the board and the 'full bucket' lockout switch and any other safety controls...If the board is good and no switches are tripped or off, then power should be leaving the circuit board and going to the fan and compressor,,, is the fan running? If the fan is running but not compressor, disconnect the power and check the wire terminal for burnt connections, or bad thermal overload switch....If the unit has low refrigerent lockout switch, it could be tripped...If you can reset this manually, do so....If not, you could have developed a refrigerant leak... The compressor could be seized...If you have an amprobe check the amp draw on startup, if it's seized it will draw LRA for 3 to 5 sec before going off on overload...The humidistat can be checked with a continuity tester, as can the 'full bucket' switch and others...I wouldn't worry about the thermistor...

You maybe correct that the sensor is of the capacitance proximity type, similar in operation with an elevator non-movable type floor selection switch. By sensing changes in capacitance as humidity /conductivity level changes.

The electronic processing circuit may be at fault that replacing the sensor will not change anything! You may need the help of a pro in electronics to be able to trace and troubleshoot to component level. Else you may need to order a new replacement board and resort to troubleshooting by substitution, which may cost more? Call the manufacturer for customer assistance / guidance. Good luck1

Humidity senor is a delicate sensitive control .Usually two thermistors are used to measure the dry bulb and wet bulb and hence the humidity. In case if some hygroscopic nature of some slats such as CACl2 ,LiCl2 etc. these materials must have lost their electric resistances and hence senor is not working.

In typical solid state humidity sensors it is a set of two matched thermistor elements: One is hermetically glass encapsulated in dry nitrogen, the other is exposed to the environment...

glass encapsulated thermistor

Thermistors differ from resistance temperature detectors (RTD) in that the material used in a thermistor is generally a ceramic or polymer, while RTDs use pure metals. Negative temperature coefficient (NTC) thermistor, bead type, insulated wires...

Here's a link to a supplier...http://www.thermistor.com/references/QTI_newcatalog.pdf

I don't think the sensor he is referring to is the humidity sensor, I believe it is a capacitive level sensor for the holding tank. They tend to use capacitives because they are immune to influence from other environmental issues and can sense directly throiugh plastic.

Although this might be a capacitive sensor, most likely the sensor itself has the detection circuit built into it and all it does is close a switch that is read by the PC board. To do otherwise would have been more costly for the Dehimidifier mfr. So if you can see three wires on the sensor, one is power to it, the others are the signal and common. If you cannot determine which is which, it should not be a problem to briefly touch one to another to see if you get any response. Capacitive sensors use very little power so there is not likely to be enough energy in the circuit to do any damage if you get it wrong.

Assuming that the compressor works fine you could always bypass the electronic control and wire one of these in series with the hot (black in the US) wire....

Ranco DH55 Dehumidistat Switch, White by Air King

It's line voltage and available from Amazon for $21. Not as elegant as the electronic variety but not as fussy either.