Testing a humidistat is a pretty simple task and can be done easily with a volt-ohm meter. Here are the tools that you need as well as the steps to help guide you through this task.
Step 1 - Test the Meter
Start off by turning the meter off completely and then testing it to make sure that it is working properly. It needs to be on the RX1 setting now to test this and also later to test the humidistat.
Step 2 - Attach to Humdistat
Once you get the meter working, attach the ends to the volt-ohm meter. Once it is connected you can turn the knob all of the way to the right for the humidistat.
Step 3 - Test
Now, move the knob back to the left slowly as far as it can go. Watch the meter as you are turning to make sure that the ohms are being measured. If it stays at zero, you have a problem and it needs to be fixed or replaced. If you continue to get a reading, then your humidistat is working properly. You can also check to make sure the overflow switch is working by attaching it to the meter and checking for a reading.