Dehumidier Icing Over Since Central Air Installation

7 years ago

Hi all,

Since we installed central air, I noticed that our dehumidifier's coils on the back have been icing up. We installed the central air system in our home a few weeks ago. The dehumidifier is located in the basement and is about 20 feet from the furnace. They are separated by a stair wall. The dehumidifier is sited over a sump pit. I turned it off to defrost the huge chunk of ice last night. I turned it back on this morning as the high today will only be in the upper 60's (not warm enough for the central air to kick on).

Could it be that the new central air system is making the basement too cold for the dehumidifier to run properly? Or, do you think the dehumidifier is broken?

Do we even need to run a dehumidifier if we have central air? If not, should we open the furnace vent registers in the basement to allow the cold air to cool the basement?

Thank you.

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Comments (3)

functionthenlook
7 years ago
last modified: 7 years ago
Our dehumidifier did that when it got below a certain temp. Our new HVAC also controls the humility in the house so depending on your AC you might not need the dehumidifier. We keep our basement gameroom air vents closed in the summer because it gets very cold down there in the summer. But we don't have a door from the up stairs to the downstairs.
DavidR
7 years ago
last modified: 7 years ago
Icing can certainly happen because of low temperature around the dehumidifier. Only you would know whether it's colder down there than it was before you installed the air conditioner. If it is, presumably the hvac system has vents in the cellar.

Normally, though, the defrost thermostat in the dehumidifier keeps ice from forming. In an older dehumidifier with a mechanical snap-button defrost thermostat, when the ambient temperature is low, you'll usually hear the compressor cycle on and off while the fan continues to run. This is preventing ice-up. Failure of these mechanical thermostats isn't uncommon.

I've also run across a few low-end older dehumidifiers that didn't even have a defrost thermostat. Those units just couldn't be used on cool days. You shut them off in the fall and left them off until summer came around again.

All the newer (last 10 years or so) dehumidifiers I've seen have had electronic sensors, which are more reliable. They have other failure modes, though.

Make sure that the dehumidifier's chiller coils aren't clogged with dust and dirt. The unit's fan has to be able to pull air through them freely.

As a quick and dirty fix, you might try aiming a box fan at the back of the dehumidifier,. That will increase the air circulation around the chiller coils and help to reduce icing.

I've never tried using an air conditioner to reduce cellar moisture. It seems to me that since the air in a cellar is already fairly cool year-round, cooling it enough to condense out excess humidity would make it pretty chilly down there. But as I say, I have no experience there. Others may know more.
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PRO
GN Builders L.L.C
7 years ago
Yes, the most common reason is the temperature in the room is to cold. Most units designed to work when a room temp is above 65 degrees.

Also if the humid-i-stat is not reading the temp right, the compressor will keep running and that will cause the coils to freeze-up.