Air handler repair and replacement: what fails and what replacement involves

What is inside an air handler

AHRI, the Air-Conditioning, Heating, and Refrigeration Institute, says the evaporator coil is typically located above or near the air handling unit. AHRI says refrigerant flows into the evaporator coil where it absorbs heat.

An installer's guide from Oxbox lists what one line of air handlers includes. It names a multi-speed blower motor, condensate drain pans, primary and secondary drain fittings and a filter rack. The same guide lists field-installed electric heater kits as an accessory.

AHRI says the inside components may be located in a crawlspace, basement, attic or closet.

What tends to fail and why

The sources we read do not rank failures by how often they happen.

The Oxbox guide says reduced airflow can shorten the life of the system's major components. Its list includes the motor, the evaporator coil and the compressor. The EPA says the condensing unit contains the condenser coil and compressor. The Oxbox guide also lists limits, elements and heat relays. ENERGY STAR says a dirty filter can increase energy costs and damage your equipment, leading to early failure.

ENERGY STAR says a dirty coil reduces the system's ability to cool your home and causes it to run longer. See the evaporator coil guide for cleaning.

The drain matters too. ENERGY STAR says a plugged drain can cause water damage in the house and affect indoor humidity levels.

Wiring and motors round out the list. ENERGY STAR says faulty electrical connections can cause unsafe operation of your system and reduce the life of major components. For the fan motor itself, see blower motor repair.

Repairs that make sense and when to look at replacement

The EPA says homeowners can maintain and repair their systems throughout the useful life of the equipment. For an existing R-410A air conditioner, it says a homeowner can replace a faulty component (for example the condensing unit or indoor coil) with a similar R-410A component.

The EPA also says systems may be repaired over time. It lists availability of components, energy efficiency and total maintenance costs as factors for deciding whether to repair or move to a new system that uses a lower-GWP refrigerant.

The 2009 ENERGY STAR guide gives warning signs worth noting. One is when your equipment needs frequent repairs and your energy bills are going up. It says the age and condition of the equipment may have made it less efficient.

The broader decision is in repair or replace.

Why the indoor and outdoor units are replaced as a pair

AHRI says split systems typically consist of an indoor (coil) unit and an outdoor (condensing) unit, specifically designed to work together. A split system is one with an indoor half and an outdoor half. AHRI says refrigerant flows between them through copper tubing.

The 2009 ENERGY STAR guide says it is very important to replace both units at the same time. It says a new outdoor unit without a new indoor unit is likely to result in low efficiency, and may lead to premature failure. AHRI says that, at worst, improperly matched units can create undue stress on your cooling system, resulting in premature failure.

UF/IFAS Extension says to replace both indoor and outdoor units if the units do not match in age, refrigerant, or efficiency.

The refrigerant can force the choice. The EPA says a broken R-22 outdoor condensing unit cannot be replaced with an R-410A one. The EPA says the R-22 indoor coil would not be compatible with R-410A due to the difference in pressures, and R-410A is not listed as acceptable by its Significant New Alternatives Policy (SNAP) Program as a retrofit for R-22 systems, so the whole system would need to be replaced. For residential air conditioner split systems, the EPA says replacing both the condensing unit and indoor coil counts as a new system for purposes of its Technology Transitions Program, even if the refrigerant lines are unchanged. What that means for the refrigerant a new system can use is covered in R-410A after 2025.

What a replacement involves

AHRI says a qualified contractor will verify that the system is properly matched by giving you a reference number or a certificate of certified performance. That number can be looked up in the free AHRI directory of certified products.

The ENERGY STAR quality installation checklist asks the contractor to do several things. It says to provide adequate room around the equipment for service and maintenance. It says to show you how to change the filter(s). It also says to confirm that the refrigerant charge and the airflow across the indoor coil meet the manufacturer's recommendation.

The Oxbox guide adds installer steps. It says secondary drain pan kits are recommended when the unit is configured for the horizontal position over a finished ceiling or living space. It says to test the condensate drain pan and drain line after installation is complete. It calls for a minimum clearance of 24 inches for filter, coil or blower removal. It also says to consult local codes for specific requirements.

UF/IFAS Extension says to make sure the inside coil can be reached for its annual cleaning. It also says to obtain a written contract or proposal before your contractor installs a new system.

Florida notes

UF/IFAS Extension says that if you have the option, choose a conditioned space for the air handler. It lists a more favorable environment, a central location that can minimize duct lengths, easier access for maintenance, and air leaks that occur in conditioned space as the advantages.

Among the questions it suggests a contractor ask a homeowner is whether there have been any problems with condensate drainage. If the unit is in an attic, ask whether a replacement is the time to move it, and see where an air handler goes.