How to Fix the Most Common Air Conditioning Problems? . If you central air conditioning system stops working during a brutal summer heat wave, you could be waiting days, if not weeks, for an appointment with a repair technician to fix it, and it’s probably going to cost a few hundred dollars. However, if you’re comfortable working around electricity and willing to spend less than $100 on parts, you can probably repair your air conditioner yourself in about two hours.

Read More : Air Conditioning System Design Manual 2nd Edition
We talked to local HVAC repair technicians to get their best do-it-yourself AC fan repair and maintenance tips. These tips will help you with the most common “low cooling” and “no cooling” problems.
You’ll need a few basic tools: multimeter, a voltage detector, an assortment of insulated screwdrivers and a socket set.
If these AC repairs don’t work, at least you’ve covered the most common failures, and your service guy can concentrate on finding the more elusive problem. Plus, with the new parts, you’ll likely add years of breakdown-free air conditioning. Here’s how to start.
Why Is My Air Conditioner Not Cooling the House?
Make Sure the Problem Isn’t the Furnace
Set your thermostat to AC mode and lower the temperature setting. If the furnace fan kicks in, the problem isn’t in the furnace. If the fan doesn’t run, try resetting the furnace circuit breaker. If the fan still won’t start, call a pro — the fixes shown here won’t work.
Next, check the outside condensing unit. The compressor (which sounds like a refrigerator) and fan should be running.
Read More : Refrigeration, Air Conditioning And Heat Pumps 5th Edition
Caution: Turn Off the Power
Turn off the A/C and furnace breakers in the main electrical panel before pulling the outdoor disconnect or removing the condensing unit’s access panel. Then use a voltage tester on the wires coming into the contactor to make sure the power is really off.
AC Doesn’t Work? Buy Parts
The AC contactor (relay) and start/run capacitor(s) (see illustration below) fail most often and are inexpensive. So it’s a safe bet to buy and install those parts right away, especially if your air conditioning service unit is older than five years. The condenser fan motor can also fail, but it runs about $150 — hold off buying that unless you’re sure that’s the culprit.
To buy replacement parts, find the nameplate on the condensing unit (not your furnace). Jot down the make, model and serial number (or take a photo). Get the parts at an appliance store, furnace dealer or online.
Anatomy of a Central Home Air Conditioner
Central home air conditioner service systems consist of two major components: a condenser that sits outside your house and the evaporator coil (often referred to as an A-coil) that sits in the plenum of your furnace or air handler. The refrigerant in the A-coil picks up the heat from your home and moves it to the outdoor condensing unit. The condensing unit fan blows outside air through the condensing coil to remove the heat. The condensing unit houses the three parts replaceable by a DIYer: the AC contactor, the start/run capacitor(s) and the condenser fan motor. The condensing unit also houses the compressor, but only a pro can replace that. The A-coil has no parts that can be serviced by a DIYer.

Read More : Principles Of Heating, Ventilation And Air Conditioning
Shut Off the Power
- Open the electrical box next to the condensing unit and pull the disconnect block straight out.
- Check inside the box with a voltage sniffer to make sure the power is really off.

Clean the Condenser Coils
It’s really easy to clean an air conditioner condenser, and it’s one of the regular maintenance tasks that will extend the life of your unit.
- Aim your garden nozzle upward into the top of the condenser coil to remove the crud buildup under the lid.
- Work all the way around the coil. Then aim the nozzle down and flush the debris down the coil fins.
- Adjust the nozzle to a gentler stream and shoot water directly into the coils to flush out any remaining debris.

Read More : Refrigeration And Air-Conditioning Technology
Test the Fuses
Many disconnect blocks contain two cartridge fuses. Check them before you proceed with repairs. A blown fuse is a sign of a failing part inside the condensing unit. So don’t just replace it and think you’ve solved the problem. Instead, replace the parts, install new fuses, and fire up the unit. If it blows again, call a pro—you’ve got more serious issues.
How to Check Fuses In the Disconnect Block
- Set your multimeter to the lowest Ohms scale and touch the red and black leads to opposite ends of each fuse.
- If you get a numerical reading, the fuse is good.
- A zero, a minus symbol, or an infinity symbol (∞) indicates a blown fuse.

Inspect the Inside of the Access Panel
Follow the electrical conduit from the house — that’s where you’ll find the access panel. With the power off, remove and store the access-panel retaining screws and remove the panel. Before you replace any parts, check for rodents’ nests or evidence of chewing on wires and electrical connectors.
If you find broken wires or chewed insulation and can safely handle electrical repairs, discharge the capacitor first. Then repair the wires and clean out the nest.
Read More : What Is the Difference Between AC and DC Motors?
How to Discharge a Dual Start/Run Capacitor
- Remove the capacitor from the retaining bracket.
- Then touch an insulated screwdriver between the HERM (or “H”) terminal and the COMMON (or “C”) terminal.
- Do the same between the FAN (or “F”) terminal and the “C” terminal.
- On single-mode capacitors, just make a short between the two terminals.

Replace the Start/Run Capacitor(s)
All air conditioning service units have at least one capacitor. The capacitor stores electricity and releases it during compressor and condenser fan startup to give both motors an extra jolt of power. And it smooths out voltage fluctuations to protect the compressor and condenser fan motor from damage.
Capacitors can degrade slowly, providing less startup power over time. Or they can fail in an instant. Gradual capacitor failure can go unnoticed for a long time, stressing the compressor and condenser fan motor windings, resulting in their early failure. Since capacitors are cheap, it pays to proactively replace yours about every five years.
Read More : What is Motor Starter?
How to Replace a Capacitator
- Take a photo of the wires before disconnecting anything (you may need a reference later on).
- Discharge the stored energy in the old capacitor.
- Use needle-nose pliers to pluck one wire at a time from the old capacitor and snap it onto the corresponding tab of the new capacitor. The female crimp connectors should snap tightly onto the capacitor tabs.
- Wiggle each connector to see if it’s tight. If it’s not, remove the connector and bend the rounded edges of it so it makes a tighter fit on the tab.
- When you’ve swapped all the wires, secure the new capacitor.
WARNING: Discharge the capacitor before disconnecting wires or removing it from its bracket.

Read More : What Does ACC Mean in a Car?
Replace the AC Contactor
An AC contactor is a $25 mechanical relay that uses low-voltage power from the thermostat to switch 220-volt high-amperage current to the compressor and condenser fan. AC contactors can wear out and are at the top of the list of common air conditioning service failures. Even if your AC contactor is working, it pays to replace it every five years or so. Unscrew the old AC contactor before removing the wires. Then move the wires to the new unit.
- Yank a connector off the old contactor and move it to the same location on the new part.
- Tighten the connectors where needed.
- Secure the new contactor in the condensing unit.

Read More : Difference between AC Drives and DC Drives
How to Test Your Repairs
- Reinstall the access panel and disconnect block.
- Turn on the circuit breaker and furnace switch, then set the thermostat to a lower temperature and wait for the AC to start.
- The compressor should run and the condenser fan should spin.
- If the compressor starts but the fan doesn’t, the fan motor is most likely shot.
- Shut off the power and remove the screws around the condenser cover.
- Lift the cover and remove the fan blade and motor.
- Reinstall the blade and secure the cover.
- Then repower the unit and see if the fan starts.

Read More : How to Control Electric Water Heater Using Switches?
How to Repair a Home Air Conditioner?
Check the Breaker or Fuse Panel
A common issue that can occur with the home air conditioning system is that a power surge or short could cause the breaker to trip or a fuse to blow. If the air conditioner doesn’t seem to have power, check the breaker panel or fuse panel. Flipping a breaker back into position or replacing a blown fuse should resolve the issue, but if the same problem happens again, you may have a more serious electrical problems that should be handled by an air conditioner repair professional or an electrician.
Change the Filter
When set at the correct temperature, the air conditioner should blow cold air, not warm or hot air. If this occurs, the system may have a dirty air filter. Replacing the air filter on an HVAC system is relatively easy and should be included as a part of your regular maintenance schedule. Remove and replace the clogged filter with a new filter, making sure that the new filter is installed in the correct direction as indicated by the arrows on the body of the filter.
Test the Thermostat
Another common cause of problems for your air conditioner is the thermostat. This piece of the system is essentially the brains of the air conditioner, where you can set the exact temperature at which you want the air conditioner to activate. However, if the batteries in the thermostat are dead or the low voltage wire connection is loose, then the thermostat cannot send a signal to the air conditioner to tell it to turn on. Replace the battery or check the low voltage wire connection to restore power to the thermostat.
If the thermostat has power, then the issue may be because the temperature is set too high. Lowering the temperature should activate the air conditioner. Though, in some cases the thermostat is placed in direct sunlight or positioned in an area that is prone to cool drafts. If this occurs, the temperature reading on the thermostat may not accurately gauge the temperature throughout the home. Consider moving the thermostat yourself if it is a battery-powered device or have an air conditioning professional relocate the thermostat to a more suitable location if it is hardwired to the HVAC system.
Read More : How to Size and Find the Numbers of Ceiling Fan in a Room?
Remove Ice Build-Up
In some circumstances the air conditioner may operate for an extended period of time in an attempt to lower the temperature within the home. During this time, ice can build up on the air conditioner. The fix for this is easier than most. Either turn the cooling system off, so that only the fan operates, or simply turn off the HVAC system. This will allow the ice to melt on its own, freeing the air conditioner.
Clean the Vents
Cooled air needs to be forced through the ventilation system so that it can reach the furthest areas of the home, but if the vents are closed, blocked, or partially blocked, then it can lead to inadequate or uneven cooling. Check the vents throughout the home to make sure that they are open, clean, and that nothing is sitting on top of or in front of the vents, like an area rug or furniture.
Clear Space Around the Compressor
Depending on your HVAC setup, the compressor could be positioned at the front, side, or back of the home. In most cases, there is a substantial amount of space around the compressor to allow for unimpeded air flow. However, if the compressor is located in a garden, under trees, or close to the bushes, then extensive growth during the warmer months of the year can obstruct the function of the air conditioner.
Trimming down any bushes, trees, and other foliage should prevent the compressor from overheating or becoming obstructed. Make sure there is about two to three feet of space around the unit and about five feet of clearance above the unit.
Read More : What is the Right Wire Size for a 30A Breaker and Outlet?
Inspect the Air Ducts
Ensuring the vents are open, clean, and clear of obstructions is necessary for even, efficient cooling throughout the home. However, even with clean vents the airflow can be restricted if the ducts are too dirty. Inspect the air ducts for signs of significant dust, hair, dirt, and debris build-up. You can typically vacuum a short stretch of air ducts, but for longer runs it’s recommended to call an HVAC maintenance professional to clean the ducts throughout the entire home.
Clean the Evaporator Coils
When the evaporator coils are dirty, it can reduce the cooling output of the air conditioner. If the issue is not resolved, you may notice that the air conditioner is not cooling or it is cooling inadequately to lower the temperature in the home. In some cases, a dirty evaporator coil could also cause the air conditioner to turn on and off repeatedly.
Check your HVAC system to determine if the evaporator coils are accessible. If the evaporator is accessible, it will be located behind foil-wrapped insulation at the front of the plenum box. Turn off the air conditioner, then remove the tape and the screws holding the access plate in position.
Use a stiff-bristle brush and a mild detergent to clean the entire evaporator unit. You can use a small hand mirror to help see what you are doing. Also, make sure to clean the collection tray below the evaporator unit, then use a wet/dry shop vac to clean out the drain line. Reinstall the access plate and tape the insulation back into position.
Read More : How to Test Car Thermostat Without Removing It
Clean the Compressor Coils
Dirty compressor coils can cause just as many issues as dirty evaporator coils. Head outside to the compressor and inspect the coils for dirt, dust, and debris. Use a mild detergent and a soft-bristle brush or microfiber cloth to clean the coils. After cleaning the coils, take a few minutes to disconnect the condensate drain line and use the shop vac to suck out any obstructions.
Examine the Coolant Lines
Most air conditioning system use a refrigerant known as Freon as a coolant. If the coolant lines are damaged, then there could be a leak in the system. When the coolant levels are too low, the air conditioner will not be able to properly cool the home.
Replace any damaged or worn insulation on the coolant lines and check for leaks. If you spot any leaks or notice the coolant levels are too low, contact an air conditioner repair professional. Do not attempt to patch the leak or charge the system’s coolant lines.
Read More : Symptoms Of Bad Ac Compressor In Car