Dehumidifier repair

Rich,

I don't think anyone can advise you without seeing the circuit diagram.

Dave M.

For starters, give it a thorough cleaning. Specificallym anything which reduces the airflow through the unit may be the cause of it short cycling.

Are we talking about the same unit, or are you saying you have a different one? Why do you assume it needs a humidistat?

Gary R. Lloyd CMS HVACR Troubleshooting Books/Software

Define "short cycling". I've heard several usages of this term, and curious which you are using.

I will check today, however it has only been in service one summer.

Yes, same unit. I understand the humidistat starts it when humidity goes up, and turns it off when humidity reaches a lower level, thus my suspicion of the humidistat.

The unit runs and water drips off the coil as it should, but only for a short time. Then another short time later it starts again, only to run another short period of time.

On a dehumidifier, the colder the evaporator coil the more moisture is removed. For this reason, the unit is designed to run close to freezing temperatures. Any reduction in airflow through the coil drops the coil temperature. If the coil temperature drops below freezing, the defrost thermostat shuts the compressor off until the coil is defrosted.

Is there any visible frost on the coil when it shuts down?

Gary R. Lloyd CMS HVACR Troubleshooting Books/Software

No, just water.

Thanks, Rich

Humidistats are notorious for quickly losing their calibration, to the point where I have long considered them useless. I have been told that todays humidistats are much better in this regard, and that electronic humidistats are far superior to mechanical humidistats, but I have seen no authoritative studies on this.

In any case, the defrost thermostat is the more likely problem here.

Gary R. Lloyd CMS HVACR Troubleshooting Books/Software

Thank you very much, that's pretty much the answer I was hoping for!

Rich

The most likely problem is the defrost thermostat shutting down the compressor, mistakenly thinking there is frost on the coil.

This thermostat will have a sensor that is physically in contact with the coil somewhere. You can check it by physically detaching the sensor from the coil (let in hang in the air) and seeing if it still short cycles.

Gary R. Lloyd CMS HVACR Troubleshooting Books/Software

This makes sense, however it is now too cold to run the unit. Before you posted this, I had decided to strip everything out and ordered a humidistat made for an old Fridgidaire model. I'm going to run it without a defrost thermostat. In my research I have learned that they were an option on many units. I can always add one later if needed.

Thanks again for your help, Rich