Any HVAC people out there?

[Kurt Veltman]

It is dehumidifier season in Michigan again, and I'm hoping there is an HVAC person out there that can tell me what's going on with my dehumidifier. It has worked fine for many years, but lately the coil has been frosting over. I have let it run overnight only to find a nearly solid block of ice around the coil in the morning. If I turn it off, thaw the ice, and turn it back on, it freezes up again. I didn't run it at all last night and it was 61% at 61 degrees in the basement this morning. The only time it has worked correctly for any length of time this year is when I also had a heater running in the basement. I know warmer air will hold more moisture, so is that the connection? Or is there something wrong with the dehumidifier?

Thanks for any input

[Craig Bumgarner]

Very often icing is due to poor air flow. The air is taking too long to get through the coil, so the air around the coils gets too cold and moisture freezes. Usually there is a filter and it may be clogged up with dust and debris. Otherwise, check that the fan is running well.

cb

[Kurt Veltman]

Thanks for the tip Craig. I will look into that. The unit is probably at least 40 years old, so any problems wouldn't surprise me. I have had it for years and didn't know anything about a filter, so hopefully that's it.

[Darrel Friesen]

Check and change your furnace filter as well if it's part of your forced air system.

[Kurt Veltman]

I checked for a filter - none. The dehumidifier is a stand alone unit - no central air in the house. The fan is working fine. Any other ideas? Could the temp in the basement have anything to do with it?

[Craig Bumgarner]

No filter, well that is not too surprising I guess. But if no filter, then the "many years" of dust being pulled through may be hung up in the air path inside somewhere. Most of the household dehumidifiers pull air across the coil first, then across the condenser. The condensers on these things sometimes look like a garland of tinsel and can catch considerable debris. I would think 60 degree ambient should be within the operating range of a dehumidifier unless the air flow is marginal. We use household dehumidifiers on boats at work down to 35-40 degrees. 90% of time icing is an air flow issue.

I'd make sure the coil, condenser and everything in the air path is really clean and the air coming out of the unit feels strong. My HVAC guys here at work tell me air flow is hard to judge. They use a simple mechanical air flow gauge and are frequently surprise when air flow is out of spec. Not that you need to get one of these, but you get my point. You could try putting a separate fan blowing in the same direction as the onboard fan to see if boosting airflow has any effect. Regardless, try taking the cabinet and support structure apart as far as you can and clean everything as best you can.

The other possibility is a low freon charge, in which case, it is time for a new unit. These things are not usually designed to be serviced and even if it were, the cost of repairs would quickly exceed the cost of a new one.

[Kurt Veltman]

I'm assuming the condenser on this one is the thing that look like a little car radiator. It looks like it could stand to be blown or vacuumed out. I'll give that a shot.

[Craig Bumgarner]

Yeah, that sounds like it. The refrigerant coil is usually, well......, a plain coil of tubing without fins in the back. The condenser usually has some form of heat dissipation fins or that "tinsel" I was referring to. It might well look like a radiator, and of course that means they want the air to go through the fins and probably channel it that way. If clogged, then low air flow.

[Kurt Veltman]

Craig, for the time being (until I can blow out the condenser) I took the front grill off the unit. I'll see in the morning if it seems to have improved it's function.