Sears Knowledge Center

Air Conditioner Troubleshooting: DIY Repair or Repairman?

AC unit

When your air conditioner breaks down, it can be daunting to know how to tackle the project ahead. With an expensive and enclosed system like an air conditioning unit, it's tough to figure out the difference between simple home repairs or potentially dangerous technical fixes. We compiled some of the most common problems homeowners face with their air conditioners to determine whether you can tackle them yourself or if you should call in a professional. 


Problem: Condenser unit won't start

Cause: Lack of power, run start capacitor failure, clogged condensate line, mechanical failure, obstructions

Symptoms: Inadequate cooling, system won't start

DIY/Call for Service/Replace: May be able to repair

The condenser portion of common split-system air conditioners holds many of the electrical elements, meaning most problems can be traced to that complex box. If the condenser doesn't work, a few different culprits could be behind it.

First, check the power. If the system kicks on when the thermostat calls for air conditioning, your power is fine. If it’s not kicking on, check the circuit breaker. A storm or other incident can occasionally flip your circuit breaker, cutting off the power to your air conditioner. However, if it trips the circuit breaker again within the same season, you likely have a different electrical problem. If this happens, call a technician, who will be better equipped to diagnose it.

If the power supply checks out, move on to different possible solutions. Everything from condensate lines to mechanical failures can cause your air conditioner to shut down or struggle to work properly. If none of the solutions below fit your problem, call a technician to identify your issue.


Problem: Dirty air filter

Cause: Infrequent filter changes, air pollutants

Symptoms: Inadequate cooling, poor air quality

DIY/Call for Service/Replace: DIY Repair

Air filters are quick and easy to replace; doing so regularly can save you from expensive repairs down the road. Clogged air filters lessen airflow into your air conditioner coils, making the system work harder than it should. That unnecessary strain can shorten the life of many elements in your air conditioner, which can lead to needing to replace the whole unit.

The general recommendation is to replace the filter whenever it gets dirty, generally every 30-60 days. Many filters can look clean despite being full of dust, so pull your filter out to examine it. Hold it up to a light fixture, and if it looks opaque, it means that your filter is filled with dirt. If your household is full of people and pets, check more often. For those with smaller households, less frequent checks are fine.

Whether you’re inserting your new filter or replacing the old one, be sure the arrow on the edge is facing the furnace. Though a filter will work in either direction, its performance will improve when it’s facing the right way.

When buying new filters, look at the MERV, or minimum efficiency reporting value, rating. The rating runs from 1 to 20, though most residential filters top out at 12. Higher-rated options may filter out more dust, but you shouldn't necessarily grab the highest-numbered filter you can find because better filtering can require more power to move the air through. Check to see what MERV rating is recommended for your system's capabilities.


Problem: Clogged condensate line

Cause: Dust or debris buildup, improper installation

Symptoms: Leaking water, flooded floors, unit won't turn on

DIY/Call for Service/Replace: DIY repair

While air conditioners are now used for temperature comfort, the first air conditioner was created as a dehumidifying device; cool air can't hold as much moisture as warm air. So as your unit works, condensation is formed, collected and drained away thanks to a condensate pan and drain line. Dust and debris can fall into the condensate pan and occasionally clog the line.

Though a clogged condensate line may seem minor, it can lead to major issues. Many air conditioner models feature a switch that will turn the whole unit off when a condensate pan is full, in order to avoid flooding. Those that don't can leak water onto your floor or ceiling, if the unit is located in the attic.

This is a simple repair to complete.

Problem: Noisy outside unit

Cause: Debris in fan, loose screws, motor needing lubrication, bent coil fins

Symptoms: Buzzing, rattling, humming or banging noises

DIY/Call for Service/Replace: May be able to repair

Many issues that cause your outside unit to make excess noise are easily fixable. Turn off the power to your unit at the circuit breaker before you go through the steps to repair it.

Debris can easily fall into the fan, causing a racket and doing damage to both your fan and its motor. Clear any pieces that have fallen in. If there was any debris in the fan, check to make sure it hasn't damaged or bent the fan blades. Contact between the blade and its housing can cause a lot of friction over time, so even a small bend in a blade can lead to a broken air conditioning unit. If blades are touching anything, gently bend them back into shape.

Other seemingly small issues can cause headaches as well. The regular vibrations of an air conditioner can rattle any loose screws. Check all internal and external connections, including motor mounts and the fan's spindle. If the sounds seem to be coming from inside a motor, adding a little oil could eliminate noises. Add this step to your annual air conditioner maintenance list to ensure you don’t have problems down the road.

The coils that are at the core of your outside unit could also be the source of your problem. Debris can also collect here, but it can gently be brushed away. We recommend using a garden hose to rinse off the unit's fins. Though it might sound like a good idea, leave the pressure washer in the garage; too much power can actually damage the fins, harming your system and creating even more noise.

If none of these steps solve your problem, it's time to call a technician. Strange noises can be indicative of a variety of major issues, so once the easy repairs are crossed off, a professional is needed.


Problem: Contactor failure

Cause: Bugs or debris in unit, mechanical failure

Symptoms: Coils ice over, compressor won't kick on

DIY/Call for Service/Replace: Call for service

A contactor functions as the switch that helps regulate your home’s temperature. It works with the thermostat to turn the air conditioner’s compressor on and off, keeping your home the desired temperature. When the thermostat triggers the contactor, it closes the circuit, letting electricity flow to the compressor and condenser fan. When bugs or other debris get into the contactor, the contactor can't close the circuit. The condenser will never kick on, and you won't get cooled air. Though many contactors are now built enclosed to keep debris from interrupting the circuit, older models may not be.

The other way a contactor can fail is if the switch breaks down and stays closed, keeping electricity flowing even after the thermostat has told it to disengage. That can lead to the coils icing over, which will end with a costly replacement if it’s not repaired in time. As with any time your coils freeze, immediately turn the system off, but keep your fan running to prevent further damage.

If you suspect a contactor issue, it's best to call a professional in for the repair. The contactor is a key part of your air conditioner's electrical system, and electrical fixes are best left to the professionals.


Problem: Refrigerant leaks

Symptoms: Low refrigerant, inadequate cooling, frozen evaporator coil, condenser cycles frequently (turns on and off)

Cause: Vibration, aging, physical damage

DIY/Call for Service/Replace: Have repaired or replaced

Air conditioner coolant runs in a closed system, moving through the evaporator to the condenser and back again. That closed system means that the coolant that comes with the system should be fine for the life of the machine, without needing to be replaced or topped off. So when a system needs refrigerant, it typically means the coil has sprung a leak.

Running your air conditioner with too little coolant causes it to overwork, breaking the unit down faster. It also changes the temperature at which the coil will freeze, meaning the unit could frost over and become less efficient. If the coil starts freezing, immediately turn your system off to prevent major damage to the evaporator.

When dealing with a refrigerant leak, it's important to consider the benefits and costs or repairing versus replacing your unit. Due to environmental regulations, older machines running on R-22 (commonly called Freon), as opposed to the more environmentally friendly R-410A, are being phased out. That means R-22 coolant and the parts for machines that use it are growing more expensive as they become rarer. As the average cost for a pound of Freon hovers near $100, a leak that demands a few pounds of coolant, along with repair costs, can match or exceed the cost of a new machine.

Once you've decide to repair or outright replace your machine, don't take on this project yourself. Regulations dictate you leave any work with the refrigerant inside your unit to the professionals, so call a professional.


Problem: Leaky ductwork

Cause: Improper installation, aging, lack of insulation

Symptoms: Inadequate cooling, black marks on insulation, rooms that won't cool

DIY/Call for Service/Replace: DIY Repair

Some estimates say that the average house loses 20 percent of the air moving through its ducts due to leaky ductwork. That means your system is working harder than it has to, leaving you with higher bills and a shorter system lifespan. Since the ductwork carries both heating and cooling, taking the time to repair it will pay off year-round.

Sealed ductwork is especially important in areas of your house that aren't temperature controlled, such as the basement or attic. The hot air of the attic can mix into your cooled air before it ever makes it out of the vents.

Sealing ductwork in your attic or basement is simple. With just a few minutes and a few purchases, regaining your system's efficiency can pay off dividends.

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