Common reasons why, and what to do
There could be many reasons why warm air is blowing from your vents when you turn on your air conditioning, but an often overlooked – and potentially serious reason – is if the outside unit of your AC (the condenser) isn’t turning on. The condenser works alongside the indoor unit to cool the air in your home by dispersing the heat that’s removed from the air inside the home by the inside unit.
Both units need to be running efficiently to produce cool air. So, even if the inside unit turns on, the AC won’t work unless the outdoor condenser unit is working. There are two ways to find out if the outside unit is running or not:
- See if the condenser is making any sounds. Some units are designed to have quiet operations, but there should still be a low hum. If there is no sound, the compressors and motors aren’t functioning as they should.
- Check if the indoor air handler is releasing warm air. If you place your hand against the indoor unit and it’s blowing hot air, the outdoor unit isn’t working properly. The warm air only passes through the AC system instead of going through the cooling cycle.
In addition to having a lack of cool air, other signs you could have a faulty outdoor AC unit is when you hear unusual noises, the fan on top of the unit isn’t spinning or you see water by your unit, which could suggest a leak in the evaporator coil drain pan.
Reasons Why Your Outdoor AC Unit Won’t Turn On
Here are some common reasons why the condenser unit isn’t working and what you can do to fix them.
- Tripped Breaker or Blown Fuse
If the AC’s breaker has tripped or its fuse has blown, your air conditioner will not turn on. Go to your electrical panel and reset the breaker or replace the fuse. If the breaker immediately re-trips, you’ve got an overloaded circuit, frayed wire or other electrical hazards that need fast, professional repair for your safety.
- Faulty Thermostat
Your thermostat communicates with the indoor and outdoor units. If it’s not set correctly, the AC might not turn on. Make sure there is a functional battery and check that it’s not broken and is properly calibrated. Ensure that the thermostat is switched to “cool” and set at least 3-5 degrees below room temperature. Wait a few minutes to see whether these minor adjustments clear up the issue.
- Capacitor Failure
Capacitors help start the compressor and store energy to ensure the fan blades always spin. They can sustain damage from high temperatures and power surges. A bad capacitor won’t be able to power the fan. If you notice a buzzing or humming noise coming from the outside AC unit, the capacitor may have failed and the AC condenser fan is trying to spin without power from the capacitor. Capacitors can age and wear over time, especially when the cooling system is working hard—in which case, they may need replacing from time to time.
- Fan Motor Failure
The motor keeps your whole AC system going. The fan in the condenser unit is linked to a motor, which allows it to rotate. So, a malfunctioning fan motor due to worn bearings or another issue due to lack of maintenance can cause the fan not to work and the outside AC unit not to run. If your motor has worn out, no matter what switches you adjust, the AC won’t turn on. The outside part of your AC system may pick up all kinds of dirt, including sticks and leaves, which can get caught in its components. When this happens, the fan won’t spin correctly. Ask an expert to inspect the motor and let you know if it can be repaired. If not, it’s time to replace your air conditioning.
- Frozen Coils
When your AC freezes, usually the evaporator (indoors) or condenser (outdoors) coils, you might have a problem with the air conditioner not turning on or turning on but not cooling. It’s important to turn the central air off and allow the coils to thaw completely. A dirty, clogged air filter could be the culprit when your coils are frozen. Replace and change your filter every three months to keep air flow from being restricted. Ask an HVAC service company to check the system for problems, like a blocked condensate line or malfunctioning fan.
- Tripped Float Switch
A tripped float switch in the evaporator drain pan means that the water level in the drain pan of your air conditioner has risen too high, causing a safety mechanism (the float switch) to activate and shut off the system, usually because of a clogged condensate drain line that prevents water from draining properly. When the float switch trips, the AC unit will usually shut off to prevent further water buildup. Ensure the float switch is working and not stuck. If the switch is faulty, it may need to be replaced. Regularly clean and inspect the condensate drain line and evaporator coil to prevent future issues with a tripped float switch.
- Low Refrigerant Levels
Refrigerant is a chemical compound found in copper coils in your outside air conditioning. As warm air moves over the coils, the refrigerant absorbs the heat and cools it down. If there’s a leak in the coils, refrigerant leaks out and the AC won’t turn on. Other signs include ice buildup outside the unit, warm air coming from the vents and unusual noises. If you suspect a refrigerant leak, contact a professional HVAC technician to inspect and repair the leak. Attempting to handle refrigerant yourself can be dangerous and may result in further damage to your system.
When to Seek Professional Help
Licensed professionals have the equipment and skills necessary to diagnose and repair complex problems. They can provide a more thorough and accurate diagnosis of any issues and offer targeted solutions. You should seek professional help for your outdoor AC unit if it's not turning on when basic troubleshooting steps mentioned earlier fail to resolve the issue, especially if you suspect a problem with the compressor, refrigerant leaks, significant electrical concerns, strange odors or damage to the outdoor unit itself. It's best to call an HVAC professional if you can't identify the problem, fix it with simple checks or the AC components are not easily accessible.
Preventative Maintenance
To prevent your outdoor AC unit from not turning on, you should regularly check the thermostat settings, ensure power is supplied by checking the circuit breaker, clean the condenser coils and surrounding area of debris, inspect the condenser fan for proper function and consider having a professional HVAC technician perform a yearly maintenance tune-up to inspect components like the compressor and refrigerant levels.
If you have any questions about why your outdoor AC unit isn’t turning on or if you want to schedule your yearly tune-up, your local Lennox Dealer can help.
This has been reviewed by Nick Orth, Director of Outdoor Cooling, for accuracy. Nick brings X number of years of expertise in the HVAC space.
