Using Your Air Conditioner as an Ice Maker
Does your air conditioning seem to be blowing out the registers with less force than usual?  This could be due to an ice block forming in the plenum of your furnace.

Under certain conditions the air conditioning is delivering its cooling  to the furnace faster than the furnace can blow it to the rest of the house. To fix the ice buildup, we first look for causes of reduced air flow in the furnace.  A dirty filter can cause this.  If the filter is dirty enough to block the air flow to the furnace, then the cooling cannot be removed fast enough from the furnace.  More cooling means a lower temperature in the plenum, and this causes ice to be formed.  The ice in turn further impedes the flow of the air through the furnace, and the end result is a huge ice block, which impedes the air flow to the home to such a point that the home is cooled little or not at all. In extreme cases, the ice block grows to where it is beyond the bounds of the evaporator drain pan, and can cause water to run down the side of the furnace, and out onto your basement floor.

The solution to this problem, once an ice block has formed, is twofold.  First we have to melt the ice block, and second, find the cause of the reduced air flow, or the ice will re-form the next time the air conditioner is started.


check-o! Turn AC OFF!
Turn off the air conditioner’s outdoor unit.  Just to be sure, use the disconnect outside, or turn the circuit breaker to the ac unit off in the basement.  Leave the furnace powered. (see next)

check-o! Leave Fan ON
Turn the thermostat FAN setting to ON, so that the furnace will continue to circulate your warm house air through the furnace. 

check-o! OR
ALTERNATIVELY, you could just turn the whole system off, and wait until you no longer hear water dripping – this may not stop until the following day. 

check-o! Prevention
When normal air flow is restored, proceed to the steps for Preventing the Next Ice Block before re-starting your air conditioner.


check-o! It's Probably the FILTER.
Replace your furnace filter.  If it’s a washable filter, wash it, if it’s a cardboard frame fiberglass filter, replace it once a month.  Sometimes filters can be dirty enough to impede air flow, and still look “not that dirty”

check-o! Air Circulation - Getting the cool air to work for you.
Be sure that the registers are open to all the rooms in your house.  Follow the instructions for setting your high air returns properly for air conditioning.


Once you’ve checked all the above, and the FAN ON setting on your thermostat produces full air flow, try turning your air conditioner back on.  If this has solved your problem, and your cooling is back to normal, enjoy!  Have a great summer!

If, however, the cooling and air flow once again diminish after a few hours, your problem is more serious, and you’d be advised to call our service department 414/778-4190. 
There are other causes for the Ice Block symptom, but they have to be remedied by a licensed professional.  Examples of other things that could cause the freezeup: 
  • Dirty evaporator coil (semi-major sheet metal operation)
  • improper refrigerant level (requires Wis. License to work on), and
  • numerous other adjustments and remedies.

SERVICE 414/778-4190 
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Air Comfort Systems, Inc.
635 South 70th Street
Milwaukee, Wisconsin 53214

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copyright 2008 Air Comfort Systems, Inc.

copyright 2008 Air Comfort Systems, Inc.