A/C Troubleshooting: Ice Buildup On a Furnace

Did you walk by your furnace and notice that ice is building up around the unit? That might seem surprising, considering a furnace is built for heating, but the ice is stemming from the fact that the furnace also forms part of your central air conditioner unit. It's a problem in the air conditioner-related mechanisms that's causing the ice.

Central air conditioner units have an exterior condensing unit that works to fuel the system and bring in exterior air.  There's also an inside unit that actually cools the air and circulates it into your house. In some systems, that inside air handler unit is actually inside your furnace.

Here are a couple of troubleshooting tips to figure out what's causing your ice buildup problem. Always turn off any power to the furnace before looking inside. If you feel uncomfortable doing the troubleshooting or fixing yourself, call a furnace service technician, like those at Lakeside Heating & A/C Inc., for assistance.

Frozen or Dirty Evaporator Coils

Liquid refrigerant enters the furnace from the outside condensing unit. The refrigerant goes into evaporator coils to be converted to gas, which causes the coils to become cold. A blower fan sucks in hot air from inside your house, directs it across the cold coils, and then blows it through your vents.

Those coils can become dirty or too cold, which can create an ice buildup. Dirt is fairly easy to clean off using a can of compressed air and a cleaning brush. Make sure you blow the dirt entirely out of the unit and onto the floor, or else the dirt can end up recirculating inside as soon as the unit is turned back on.

Evaporator coils that have frozen for the first time can be thawed. Set your air conditioner thermostat so that it's on fan-only mode, and allow to run for a few hours. The lack of refrigerant entering the system in this mode means that the evaporator coils will only receive the hot air from the blower fan, which will eventually start to melt the ice.

If ice buildups on the coils are a recurring problem, there's likely another problem at work.  

Low Refrigerant  

If the refrigerant in the air conditioning system is almost empty, the coils won't cool down at all and you won't receive cold air inside. But if the refrigerant is only moderately low, the state change in the evaporator coils can be thrown off balance, causing the coils to become too cold.

Low refrigerant is a problem that has to be corrected by an HVAC technician. The type of refrigerant used requires a professional license to purchase in most areas, and using the wrong refrigerant, or putting it in incorrectly, could wreck your entire system.