How To Investigate Low Air Flow Issues Caused By Your AC Evaporator Coil

Around 100 million homes in the United States have air condition systems, and this means that about 87% of all homes use an air conditioner. If you are lucky enough to have a central AC system instead of a window unit, then you probably do your best to make sure that the system is kept in great shape. If you pay close attention to the system, then you may notice fairly quickly if air flow rates start to drop. If air flow seems to have tapered off a bit, then there are some issues that you can investigate before your contact your HVAC professional. Your problem may revolve around the evaporator coil, so find out how to inspect for coil issues and possibly find your air conditioning unit problem.

Look For Signs Of Ice

The part of your AC system that sits in your basement is called the evaporator, and this is where air is cooled and then pumped through your ducts. The evaporator coil is responsible for the cooling of the air, and the coiled copper tubing can actually form a layer of ice. Surprisingly, this layer of ice can actually keep the evaporator coil from cooling the air properly. The ice creates a barrier on the outside of the coil. This prevents the coolant from interacting with the air that moves passed the tubing. Under normal conditions, the coolant will pull heat from the air through the metal coils. When ice keeps this from happening, the result is reduced air flow and sometimes warmer air coming through the vents. 

You will see some obvious signs if the evaporator coil is covered in a layer of ice. Ice can build thickly enough around the evaporator coil that it starts to expand to the metal casing of the AC unit. Look for ice on the outside panels of the AC unit and touch the cover to see if it feels cold. Also, you may see a puddle on the floor underneath the air conditioner. Ice may build and melt continuously. AC drain pans can typically handle normal levels of condensation, but the pan may overflow onto the floor when ice melts off the evaporator coil.

If you notice ice, then turn off your air conditioner for a few hours or even a full day. An overworked AC unit is one of the main causes of ice build up. As more and more air needs to be cooled by the evaporator coil, more condensation forms on the coolant coils. The condensation then freezes as cold air moves passed the water on its way to your vents. Normally, your AC unit will cycle off before the condensation has a chance to form. This will not happen if your system is struggling to keep your house cool.

If ice disappears and air flow returns to normal afterwards, then adjust your thermostat a degree or two warmer so your AC unit does not need to run continuously. If a warmer house is not comfortable, then think about upgrading your cooling system to a larger one. Larger units will turn on less often, and this will reduce the chances of ice forming. 

Clean Off Dirt

Your air conditioner will cool air that is pulled into the system through the blower. In many cases, a vent is installed that pulls fresh outside air into the system. Your AC unit may or may not have a filter attached to the air intake vent. If there is no filter, then dirt, pollen, and exterior debris can enter the system. Some of the dirt will collect on the evaporator coil as air passes by. Dirty coils will not cool air as efficiently as they should, and you may experience a drop in air flow if the coil is too dirty. If you need to change your AC filter often due to the build up of dirt and debris, then this is a good sign that your evaporator coils also may be dirty.

You can clean the evaporator coils fairly easily. Remove the top outside cover of the AC unit. The evaporator coils will sit close to the top of the appliance near the ductwork. The tubing will sit in a triangular or A-shaped formation with grates or metal fins connected to the copper tubing. You will not be able to rinse the coils and fins like the coils that sit outside your house. You will need to use a no-rinse foaming cleaner instead. Purchase a foaming AC coil cleaner from your local home store. Spray the cleaner, let it sit for 20 to 30 minutes and then replace the metal cover. 


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