Humidifier Runs but no water collected

Are you talking about a dehumidifier or a humidifier. If you are talking about a dehumidifier, it works by blowing air across a cooling coil causing condensation and the water will drip and pool. The cooling is caused by a compressor working like refrigerator, but using the effect to dehumidify. To check if the cooling coil is working there will be a metal can like in it with tubes in and out. One of the tubes should be warm(input) and the other tube should be cold, if not your compressor is not working. If freezing up, low freon. Check to see if the compressor shuts off very quickly, that would be too much freon. This is not user servicable. Now a humidifier works several different ways. One way is a fan with cloth belts rolling through water using evaporation to humidify. Another way is for a circular fan like on a motor to turn. It has a hollow piece into the water. It picks up water and then through centrifugal force aerates. One way is for a sonic humidifier. All the types have a problem with eventual calcification or mineral build up in the water handling paths. Lime-away or Concentrated Lemon Juice will dissolve this. The lemon juice is the most fun. It will turn your toilet bowl white and also remove rust stains from laundry...