AC Troubleshooting: Common Problems and How to Fix Them

When your air conditioner isn’t working properly, it can be frustrating, especially during the hot summer months. Whether your system is blowing warm air, making strange noises, or refusing to turn on altogether, your first instinct may be to call for repairs. 

Fortunately, many common AC issues can be identified and resolved without needing to call in a professional – saving you valuable time and money. HVAC.com walks you through some typical air conditioning problems and the AC troubleshooting steps that can help you get your system back on track.

1. System Won’t Turn On

An air conditioner that won't turn on can often be fixed by checking the thermostat and power settings.

AC Troubleshooting Steps:

• Check the Thermostat: Start by ensuring your thermostat is set to “cool” and that the temperature is set lower than the current room temperature. If the thermostat screen is blank, the batteries might be dead, so try replacing them.
• Inspect the Circuit Breaker: If the thermostat seems fine, the next step is to check your circuit breaker. The AC unit might have tripped the breaker – which is common during times of heavy usage – cutting off power to the system. Resetting the breaker may solve the issue.
• Examine the Power Switch: Many air conditioning systems have a power switch located near the indoor air handler and outdoor condenser unit. Make sure the switch is in the “on” position.

2. AC Unit Is Blowing Warm Air

When your air conditioner is blowing warm air, something isn’t right. An air conditioner may blow warm air if the thermostat is incorrectly set or if the air filter is clogged, which restricts airflow. Another common reason is low refrigerant levels, which can prevent the system from cooling effectively.

AC Troubleshooting Steps:

• Check the Thermostat Settings: Make sure your thermostat is set to “cool” and the fan is set to “auto” rather than “on.” When the fan is set to “on,” it blows air constantly, even when the system isn’t cooling, so you may feel warm air coming from the vents in between cooling cycles.
• Inspect the Air Filter: A dirty or clogged air filter can restrict airflow, causing the system to blow warm air. If the filter is dirty, replace it with a new one. Filters should be changed every 1-3 months, depending on usage.
• Look for a Refrigerant Leak: Low refrigerant levels can also prevent your AC from cooling effectively. Signs of a refrigerant leak include hissing noises, ice buildup on the refrigerant line, and reduced cooling capacity. If you suspect a leak, call a professional to recharge the refrigerant and repair the leak.

3. Weak Airflow from Vents

Do you have weak airflow coming from your air vents? Weak airflow can strain your air conditioner by causing it to overwork, which may lead to increased wear and tear on internal parts. If airflow is restricted for a long time, it can cause the system to overheat and potentially damage the compressor.

AC Troubleshooting Steps:

• Check and Replace the Air Filter: Start by inspecting the air filter. If it’s dirty or clogged, replace it with a new one. A clean filter improves airflow through the system and your home.
• Inspect the Ductwork: Check the ducts for any visible blockages like debris or damaged areas. Make sure all the connections are secure and well-sealed. Fix any problems you find to restore proper airflow or contact an HVAC contractor.
• Examine the Blower Motor: Look for any signs of issues with the blower motor, such as a loose belt, which can diminish its performance. If the motor appears faulty, it may need to be serviced or replaced by a professional.
• Verify Vent Openings: Ensure all supply and return vents are fully open and unobstructed by furniture or other items. Blocked vents or closed louvers on vent covers can cause weak airflow.

4. AC Unit Is Making Strange Noises

Unusual noises from your air conditioning system aren’t only annoying, but they often signal that something is wrong. Buzzing or humming sounds could indicate electrical issues, such as a failing capacitor or loose wiring. Turn off the unit and contact a professional to avoid further damage.

Rattling and banging may mean that something is loose inside the system, such as a fan blade or motor mount. A high-pitched squeal often points to a problem with the blower motor or the fan belt. 

AC Troubleshooting Steps:

• Inspect the Air Filter: A clogged or dirty air filter can cause various noises, such as whistling or humming. Replace the filter if it’s dirty, as this can often resolve noise issues and improve system performance.
• Check the Fan Blades: Turn off the AC unit and inspect the condenser fan blades for any signs of damage or obstruction. Ensure the blades are clean and free from debris, and make sure they spin freely. Bent or damaged blades may need to be adjusted or replaced.
• Examine the Capacitor and Wiring: Buzzing or humming noises could indicate issues with the capacitor or loose wiring. Inspect the capacitor for signs of wear or damage, and ensure all electrical connections are secure. If you suspect electrical problems, it’s best to contact a professional.
• Look for Loose Components: Rattling or banging noises may be caused by loose parts, such as screws, bolts, or panels. Check and tighten any loose components, including the screws on the AC unit’s casing, as well as the air handler or furnace indoors.

5. Leaking Water

Water pooling around your air conditioning unit is never a good sign. An air conditioner leaking water can cause significant damage to your home and HVAC system, such as the electrical system and insulation, leading to expensive repairs.

AC Troubleshooting Steps:

• Check the Condensate Drain Line: The condensate drain line carries away moisture that your air conditioner removes from the air. If the line is clogged, water can back up and leak out of the unit. You can try to unclog the line by using a wet/dry vacuum to suck out the blockage.
• Inspect the Drain Pan: The drain pan collects water that drips off the evaporator coil inside the indoor unit. Over time, algae and debris can build up in the drain pan, causing a clog. Use a wet/dry vacuum to remove pooled water from the pan, remove it, and clean out debris.
• Look for Frozen Evaporator Coils: If the evaporator coils freeze over, they can cause water to leak as the ice melts. Frozen coils can be caused by a dirty air filter, low refrigerant, or poor airflow. Change your air filter if it’s dirty and ensure the indoor and outdoor units are unobstructed. If the coils continue to freeze, it could be due to a refrigerant leak, which will require professional repair.

6. System Is Constantly Cycling On and Off

If your air conditioner is turning on and off frequently, it’s called short cycling. Short cycling causes excessive wear and tear on critical components, like the compressor. This constant starting and stopping can also lead to inefficient cooling, increased energy consumption, and a shortened lifespan of the unit. Airflow issues and electrical faults can cause this issue, as well as low refrigerant levels and incorrect system sizing. If AC troubleshooting doesn’t solve the problem, have your unit inspected for refrigerant leaks or sizing issues.

AC Troubleshooting Steps:

• Inspect the Air Filter: A dirty or clogged air filter can restrict airflow, leading to short cycling. Replace the filter with a clean one to improve airflow and reduce strain on the system.
• Check for Proper Ventilation: Ensure that vents are open and unobstructed. Blocked or closed vents can disrupt airflow and cause short cycling.
• Inspect the Electrical Components: Look for any issues with electrical components such as the capacitor or contactor. Faulty components can cause irregular cycling. If you notice damage, seek professional help to diagnose and repair electrical problems.

7. Frozen Evaporator Coils

Frozen evaporator coils can cause a range of issues, from weak airflow to a complete system shutdown. Prolonged ice buildup also reduces the system's efficiency, resulting in higher energy bills and a shortened lifespan of the unit.

• Turn Off the AC: First, turn off the air conditioner to allow the coils to thaw. Running the system while the coils are frozen can cause damage.
• Check the Air Filter: A dirty air filter is a common cause of frozen coils. Replace the filter and see if it fixes the problem.
• Have the Refrigerant Levels Checked: As mentioned earlier, low refrigerant can cause the coils to freeze. If replacing the air filter doesn’t fix the issue, it’s time to call a professional to check the refrigerant levels and inspect for leaks.