How to Fix Central Air Conditioners

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Home Improvement

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Central air conditioners consist of two components: the condenser and the evaporator. The condenser unit is typically found outside the house on a concrete slab. The evaporator coil is positioned in the plenum or main duct junction above the furnace.

Most central air conditioners are connected to a home’s forced-air distribution system. Therefore, the same motor, blower, and ductwork used for heating are used to distribute cool air from the air conditioning system. When a central air conditioner is in operation, hot air inside the house flows to the furnace through the return-air duct. The blower moves the hot air across the cooled evaporator coil in the plenum and then delivers it through ducts to cool the house. When the air conditioner is running but the house isn’t cooling, the problem is most likely in the distribution system.

Central air conditioners are made up of two separate components: the condenser unit,
located outside the house on a concrete slab, and the evaporator coil above the furnace.

Both the evaporator and the condenser are sealed. Therefore, unless it’s routine cleaning, a professional service person should be contacted for almost any maintenance. Central air conditioners should be professionally inspected and adjusted before the beginning of every cooling season. However, don’t let your maintenance end with this yearly checkup. While there aren’t many repairs that you can do yourself, there are specific maintenance procedures that you can follow to keep your system running at peak efficiency.

Caution: Before doing any work on an air conditioning system, make sure that the power to the system, both to the condenser and to the evaporator assembly, is turned off.

Before you begin working, let’s try to narrow down the scope of the job. Look for the issue you’re having and its solution on the chart on the next page.

For more articles on home repair, check out the following links.

  • How To Repair Room Air Conditioners: Cooling units that you mount in your window have the same job as central air conditioners, but the repair principles are different. Follow these instructions to get your unit running smoothly.
  • Major Appliance Repair: If the a/c isn’t the only thing in your house on the fritz, you can learn how to fix other machines in this article.
  • Small Appliance Repair: Once you’ve tackled the a/c, a toaster or blender seems like child’s play. Find out how to fix them here.
  • Thermostat Maintenance: To make sure there’s actually a problem with your a/c, you may want to check the thermostat, too. Learn how to calibrate a thermostat.

Central Air Conditioner Troubleshooting

Central air conditioners will require some professional maintenance, but there are many minor issues that you can quickly fix yourself. If your central a/c unit isn’t working correctly, look for the issue you’re experiencing on this chart and see if it’s something you can do yourself.

If you are having problems with your central air conditioner, this troubleshooting chart can help you identify the possible causes and solutions. The chart is divided into different sections, such as Condenser Doesn’t Run, Uneven Cooling, and Inadequate Cooling. Each section lists the possible causes of the problem and suggests a solution. For example, if your condenser doesn’t run, the problem could be that there is no power, the thermostat is set too high, the motor is faulty, or the compressor is faulty. The chart suggests checking for blown fuses or tripped circuit breakers, lowering the thermostat setting, or calling a professional if the problem is more serious. If you are experiencing uneven cooling, the chart suggests balancing the distribution system, while inadequate cooling could be due to a dirty evaporator, a thermostat set too high, or a unit that is too small. The chart also includes a section on what to do if the condenser unit turns on and off repeatedly. If you have a dirty evaporator, the chart recommends cleaning it properly. The instructions for cleaning the evaporator are provided on the next page, including how to access it and what to do if it is located in a foil-wrapped insulation or a sealed sheet metal box.

Tools Needed
To clean the evaporator, you will need the following tools:

  • Screwdriver
  • Stiff brush
  • Large hand mirror
  • Household bleach
  • Wire

Step 2: Use a stiff brush to clean the entire underside of the evaporator unit. A large hand mirror can be used to see what you’re doing. If you can’t reach the entire area, slide the evaporator out slightly. The evaporator can be slid out even if it has rigid pipes connected to it, but be careful not to bend the pipes.

Step 3: Clean the tray below the evaporator unit. This tray carries condensation away from the evaporator. Pour 1 tablespoon of household bleach into the weep hole in the tray to prevent fungus growth. In extremely humid weather, check the condensate drain and pan every other day. If there’s a lot of moisture in the pan, the weep hole from the pan to the drain line may be clogged. Open the weep hole with a piece of wire.

Step 4: Put the unit back into place, reinstall the plate, and tape the insulation back over it.

Step 5: Turn the air conditioner back on and check for air leaks. Seal any leaks with duct tape.

You may also need to clean the condenser to ensure that your air conditioning is functioning properly. Find out how to do this on the next page.

Cleaning the Condenser

Most air conditioning systems have the condenser unit located outside the house, and it is prone to accumulating dirt and debris from trees, lawn mowing and airborne dust. The condenser has a fan that moves air across the condenser coil. You must clean the coil on the intake side, so before you turn off the power to the air conditioner, check to see which direction the air moves across the coils. Here’s how to clean the condenser:

Tools Needed
To clean the condenser, you will need the following tools:

  • Grass shears or pruners
  • Spray bottle of coil cleaner
  • Soft brush
  • Fin comb
  • Carpenter’s level
  • Pry bar or piece of 2-by-4
  • Gravel or rocks

Step 1: Remove any grass, weeds or vines that have grown around the condenser unit, as they could be obstructing airflow.

Step 2: Clean the condenser with commercial coil cleaner, which is available at refrigerator supply stores. Instructions for use are included. Flush the coil clean (do not use a hose) and let it dry.

Step 3: Clean the fins with a soft brush to remove any accumulated dirt. You may have to remove the protective grille to reach them. Do not clean the fins with a garden hose, as water could turn the dirt into mud and compact it between the fins. Clean the fins carefully as they’re made of light-gauge aluminum and are easily damaged. If the fins are bent, use a fin comb, which is sold at most appliance parts stores, to straighten them. A fin comb is designed to slide into spaces between the fins. Use it carefully to avoid damaging the fins.

Step 4: Check that the concrete pad on which the condenser rests is level. Place a carpenter’s level front to back and side to side on top of the unit. If the pad has settled, lift the pad with a pry bar or a piece of 2 x 4, then force gravel or rocks under the concrete to level it.

During autumn and winter, it is important to protect outside condenser units from the elements to prevent blockage from leaves and damage from ice. A commercial condenser cover or heavy plastic sheeting secured with sturdy cord can be used to cover the unit.

If you have cleaned everything and the air is still not cool, the issue may be with the refrigerant. You can learn what to do in this situation on the next page.

Dealing with the Refrigerant

The refrigerant used in most air conditioning systems is called Freon. If the system does not have the correct amount of Freon, it may not cool properly. If you suspect a problem with the Freon, contact a professional service person to recharge the system. Do not attempt to charge the refrigerant lines yourself.

To repair the system’s coolant lines, inspect the lines running from the condenser outside to the evaporator inside the house. If the insulation is damaged or worn, it can reduce the cooling efficiency of the unit and should be replaced. Replace any damaged or worn coolant line insulation with new insulation of the same type as soon as possible, following the manufacturer’s instructions for installation.

Now that you know when to seek professional help and when to make repairs yourself, you can save money and get cool air pumping sooner using the tips in this article. For more home repair articles, check out the links below.

  • How to Repair Room Air Conditioners
  • Major Appliance Repair
  • Small Appliance Repair
  • Thermostat Maintenance


1. What are the common problems with central air conditioners?

Some of the most common problems that can occur with central air conditioners include refrigerant leaks, dirty filters, faulty thermostats, and clogged condenser coils. It is important to address these issues promptly to prevent further damage to the unit and maintain optimal performance.

2. Can I repair my central air conditioner myself?

While some minor repairs such as replacing a dirty filter or cleaning the condenser coils can be done by homeowners, most central air conditioner repairs require the expertise of a professional HVAC technician. Attempting to repair the unit yourself could result in further damage or even injury.

3. How often should I have my central air conditioner serviced?

It is recommended to have your central air conditioner serviced by a professional HVAC technician at least once a year. This will help ensure that the unit is functioning properly and any potential issues can be addressed before they turn into major problems.

4. What is involved in a central air conditioner repair?

The repair process will vary depending on the specific issue with the unit. The HVAC technician will typically perform a thorough inspection of the unit to diagnose the problem, then make the necessary repairs or replacements. This may involve replacing a faulty part, cleaning the coils, or recharging the refrigerant.

5. How long does a central air conditioner repair take?

The length of time it takes to repair a central air conditioner will vary depending on the extent of the damage and the specific repair needed. Minor repairs may be completed in a few hours, while more extensive repairs could take several days.

6. How can I prevent problems with my central air conditioner?

Maintaining regular upkeep on your central air conditioner can help prevent problems from occurring. This includes regularly changing the air filter, cleaning the condenser coils, and scheduling annual maintenance checks with a professional HVAC technician.

7. What is the average cost of a central air conditioner repair?

The cost of a central air conditioner repair will vary depending on the specific issue and the cost of any necessary parts. Minor repairs may cost a few hundred dollars, while major repairs could cost several thousand dollars.

8. How long should a central air conditioner last?

The average lifespan of a central air conditioner is approximately 15 to 20 years with proper maintenance. However, factors such as usage and climate can affect the lifespan of the unit.

9. Can I replace my central air conditioner instead of repairing it?

In some cases, it may be more cost-effective to replace a central air conditioner rather than repair it, especially if the unit is old and outdated. A professional HVAC technician can help determine if a replacement is necessary and recommend the best options for your specific needs and budget.

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