How to Repair a Home Air Conditioner

Air conditioners are essential appliances for keeping homes cool during hot summer months. Like any machine, air conditioners can break down or develop problems over time. Many issues can be repaired by homeowners with some mechanical aptitude and the right tools. Learning how to diagnose and fix common air conditioner problems can save you the hassle and expense of professional repair calls. This guide will provide step-by-step instructions for diagnosing issues and making DIY repairs to get your home air conditioner working properly again.

Understanding How Home Air Conditioners Work

Before attempting any repairs, it helps to understand the basic components and function of a home air conditioner unit. Most operate on similar principles.

The core components of an AC unit include:

  • Compressor – This is the heart of the air conditioner. The compressor pumps refrigerant through the system.
  • Condenser coils – Refrigerant flows through these coils, releasing heat from the refrigerant to the outside air.
  • Evaporator coils – Refrigerant absorbs heat from indoor air as it flows through these coils, cooling the air.
  • Expansion valve – This metering device regulates the flow of refrigerant to the evaporator coil.
  • Fans – Blow air over the evaporator and condenser coils to facilitate heat transfer.
  • Drain line – Removes condensation from evaporator coils.
  • Electrical controls – Thermostat, control board, sensors. Manage system operation.

Refrigerant flows in a closed loop, absorbing heat from inside air and releasing it outdoors. The process of phase change from liquid to gas cools the refrigerant dramatically, allowing it to absorb heat.

Understanding this basic operation will help you pinpoint issues within the system. Common problems stem from refrigerant leaks, electrical malfunctions, or breakdown of core components.

Gathering Tools and Supplies for AC Repair

Before tackling any DIY AC repair project, ensure you have the proper tools and equipment:

  • Socket wrench set – For loosening and tightening bolts/nuts
  • Screwdrivers – Phillips and flathead, standard and miniature sizes
  • Needle nose pliers – Gripping small parts and wires
  • Wire cutters/strippers – Handling electrical connections
  • Multimeter – Diagnosing electrical issues
  • Electrical tape – Protecting wire connections
  • Tube cutters – Cutting refrigerant lines
  • Torch kit – Soldering/brazing refrigerant lines
  • Refrigerant and oil – Recharging the system
  • Vacuum pump – Evacuating air from lines
  • Leak detector – Finding refrigerant leaks
  • Thermometer – Checking air temperatures
  • Brush – Cleaning condenser coils
  • Personal Protective Equipment – Gloves, goggles, ear protection

Acquiring the necessary tools and having them on hand will make the repair process smoother. Be sure to use proper safety precautions like gloves and goggles when handling refrigerant.

How to Diagnose Common Air Conditioner Problems

The first step in any AC repair is accurately diagnosing the issue. Here are some of the most common air conditioner problems and how to identify them:

Air Conditioner Not Blowing Cold Air

If your AC unit is running but not cooling properly, possible causes include:

  • Refrigerant leak – Low refrigerant levels prevent proper cooling. Check sight glass on compressor or use leak detector.
  • Clogged air filter – Restricts airflow over evaporator coils. Inspect filter, replace if dirty.
  • Frozen evaporator coils – Indicates low refrigerant charge. Thaw coils, check for leaks.
  • Broken compressor – Will not pump refrigerant properly. Use multimeter to check for power.
  • Condenser fan failure – Impairs heat rejection outside. Inspect fan operation.
  • Thermostat issues – Check thermostat settings match room temp. Test with known working thermostat.
  • Refrigerant flow restriction – Clogged filter drier or expansion device hinders flow. Requires professional service.

Water Leaking from Indoor Unit

If you notice water dripping from vents or around the indoor unit, it likely indicates:

  • Clogged drain line – Prevents condensate drainage. Disconnect and clear drain line.
  • Overflowing drain pan – Excess condensate overwhelms pan. Ensure pan is sloped properly to drain. Check for clogs.
  • Leaking refrigerant coils – Refrigerant leak causes icing then melting. Identify source of leak.
  • Leaking water valve – Corroded/broken valve can leak. Replace water valve assembly.

Loud Noise from Outdoor Unit

Unusual noise from the outdoor condenser unit may signal:

  • Broken fan blade – Causes rattling, scraping noise. Blade must be replaced.
  • Imbalanced fan – Uneven blade pitch or debris causes vibration. Clean fan, check balance.
  • Failed motor bearings – Bearing wear causes grinding, squealing. Motor must be replaced.
  • Defective compressor – Knocking or rattling noise. Indicates internal compressor failure.
  • Obstruction – Sticks or debris striking fan. Remove debris, trim back brush.
  • Loose parts – Shroud, cover or components banging against each other. Tighten fasteners, adjust parts.

Electrical Control Issues

Problems with the electrical components may prevent normal operation:

  • Blown fuse – No power to unit. Check and replace any blown fuses.
  • Tripped circuit breaker – Reset breaker, determine if short is causing tripping.
  • Faulty control board – Powers unit sporadically. Test board, replace if faulty.
  • Loose wires – Can cause intermittent function. Check connections at control board.
  • Failed sensors – Thermistors and pressure switches trigger safety shut off. Test components, replace damaged parts.
  • Thermostat malfunction – Unit won’t start or shuts off prematurely. Test thermostat, replace batteries.
  • Contactor failure – Compressor won’t start due to failed contactor. Replace contactor.

Step-by-Step AC Repair Instructions

Once you’ve diagnosed the specific issue with your air conditioner, it’s time to tackle the repair. Use the step-by-step guides below to handle some of the most common DIY fixes:

Replacing Capacitors

A failed capacitor can cause the outdoor fan or compressor to malfunction. Here are the steps for replacement:

  1. Turn off power to AC unit at breaker box and at disconnect switch.
  2. Discharge any residual electricity in old capacitor.
  3. Label and disconnect all capacitor wiring.
  4. Remove any mounting screws to pull out old capacitor.
  5. Install new capacitor with same mounts and wiring.
  6. Power on AC unit and test operation. Capacitor may need time to fully charge before working.

Unclogging Condensate Drain Line

  1. Shut off AC unit at thermostat.
  2. Locate drain line exit point outside of home.
  3. Disconnect drain line from exit point.
  4. Use wet/dry vacuum to suck standing water from line.
  5. Run drain snake or wire through line to clear clog.
  6. Flush line with water mixed with drain cleaner.
  7. Reattach drain line and monitor for proper water flow outside.
  8. Restart AC unit and check for leaks.

Replacing Condenser Fan Motor

  1. Turn off electrical supply to AC unit.
  2. Remove fan blade nut and pull off blade.
  3. Disconnect and label wires on old motor.
  4. Remove mounting bolts to detach motor.
  5. Install new motor with same mounting configuration.
  6. Connect wires matching previous labels.
  7. Reattach fan blade. Check for smooth rotation.
  8. Restore power and verify proper condenser fan operation.

Charging Refrigerant

  1. Attach gauge set to service ports to check refrigerant pressure.
  2. Determine how much refrigerant charge is needed based on gauges and unit specs.
  3. Connect refrigerant tank to suction line service port.
  4. Open tank and purge valves to allow refrigerant to flow into low side.
  5. When proper pressure is reached, close valves and disconnect refrigerant tank.
  6. Monitor system to ensure pressures remain stable.
  7. Conduct leak check, repair any leaks found.

Troubleshooting Common Air Conditioner Repair Issues

DIY repairs don’t always go smoothly. Use the tips below to troubleshoot common problems:

AC won’t turn on after capacitor replacement:

  • Wait several minutes for capacitor to charge.
  • Verify wiring matches diagram on new capacitor.
  • Test capacitor with multimeter, replace again if faulty.

Drain line clogs again after cleaning:

  • Flush with more vigorous water/cleaner mixture.
  • Run drain snake further to clear all clogs.
  • Check slope for proper downward drainage.
  • Remove accumulated sediment and scale in drain pan.

No cold air after recharging refrigerant:

  • Give system time to stabilize pressures after recharge.
  • Confirm refrigerant charge using sight glass or gauges. Add more if needed.
  • Check for leaks and recharge again after fixing.
  • Inspect other components like valves, filter drier, and condenser.

AC trips breaker after motor replacement:

  • Ensure wiring matches wiring diagram for new motor.
  • Check for short circuit in motor wiring.
  • Verify amp draw does not exceed breaker rating.
  • Make sure blade spins freely without obstruction.

Maintaining Your AC Unit

Performing regular maintenance is the best way to catch small problems before they turn into major repairs. Follow this maintenance schedule:


  • Check filters, replace when dirty.
  • Inspect condenser and evaporator coils for dirt, clear away debris.
  • Check for abnormal noises or smells.


  • Clean condenser with water, coil cleaner, or mild detergent.
  • Spray condenser fins with fin comb to straighten bent fins.
  • Clear vegetation and debris from outdoor unit area.
  • Drain and refill condensate pan to keep clean.
  • Test capacitor and relays, replace if needed.
  • Check belts and pulleys, adjust tension as needed.
  • Conduct thorough leak check, repair any leaks.
  • Check refrigerant charge.

Following proper maintenance practices will maximize the life of your air conditioner, reduce repair frequency, and deliver more effective cooling performance.

FAQs Related to AC Repair

Some frequent questions that arise regarding DIY air conditioner repairs:

Is it safe for a homeowner to make AC repairs?

Many common AC issues like drain clogs, dirty filters, and loose parts can be safely repaired by a homeowner with basic mechanical skills. More complex repairs involving refrigerant, electrics, or the sealed system should be left to a licensed technician. Use good judgment.

How can I find the refrigerant type for my AC?

The refrigerant type is usually listed on the information plate attached to the outdoor condenser unit. R-22 and R-410a are the most common in residential units. This information is needed to purchase matching refrigerant for recharging the system.

What causes coils to freeze over?

Low refrigerant charge is the most common cause of frozen evaporator coils. This starves the coil of adequate refrigerant flow to absorb heat. Low airflow from a dirty filter can also cause freezing. Be sure to thoroughly defrost and check for leaks if coils freeze up.

Why does my AC trip the circuit breaker?

Frequent circuit breaker tripping usually indicates a short circuit or overloaded circuit. Problems like seizing motor bearings, frayed wires, or too many appliances on one circuit can cause tripping. Identify and remedy the underlying issue before resetting the breaker.

How often should I change my AC air filter?

Most filters should be changed every 30-90 days, depending on run time and dust/debris levels in the home. Check filters monthly and replace when dirty. Upgrading to a pleated filter can provide better filtering while requiring less frequent changes.


Repairing your own air conditioner can be a worthwhile DIY project that saves on professional repair costs. Many common AC problems can be diagnosed and fixed with basic tools and some mechanical skill. Just be sure to observe proper safety protocols when working with electrical and refrigeration systems. Understanding how your AC operates helps identify failed components causing issues. Follow step-by-step guides to tackle repairs like drain line clearing, fan motor replacement, capacitor replacement, and refrigerant recharging. Remember to perform regular maintenance each season to get the longest life from your air conditioner. With some diligent troubleshooting and these DIY repair tips, you can beat the summer heat.