Discover why your car AC blows warm air and how to fix it. While refrigerant might be the culprit, there are other, less obvious reasons for warm AC.
One of the worst things you can experience on a hot summer day is the disappointment of a malfunctioning air conditioning system. If your car AC blows warm air, you’ll not only be sweltering, but your alertness may drop due to excessive heat. Read on to discover the most common reasons why your car AC blows hot air and how to solve the issue.
Understanding the inner workings of your car’s AC system is crucial. Every AC system is composed of two parts: the high and low-pressure sides. The table below provides a breakdown of what each critical AC component does during a single AC cycle, serving as a foundation for troubleshooting and preventing future issues.
| Pressure side | AC Working Steps | State of Refrigerant |
| High-pressure side. | 1. Compressor receives gas from the evaporator inside your car and turns it into a high-pressure gas. | High-pressure gas. |
| 2. Compressor sends the gas to the condenser. | ||
| 3. Condenser cools the refrigerant significantly, turning it into a high-pressure liquid. | High-pressure liquid. | |
| Low-pressure side. | 4. Liquid reaches an expansion valve or orifice tube where it expands and loses pressure, making it very cold. | Low-pressure liquid. |
| 5. Low-pressure liquid enters the evaporator, where it receives heat from inside your car. It quickly boils into a low-pressure gas as it cools your vehicle. | Low-pressure gas. | |
| 6. Low-pressure gas is sent to the compressor, where the cycle begins again. |
The AC is a closed system. So, if there’s any leak between these components, the system loses pressure, and you’ll get the dreaded warm air instead of blissful cool air.
If you’ve excluded the wrong thermostat settings as a possible issue, your car AC blowing hot is most likely related to the seven common reasons below.
Refrigerant leaks can be challenging to detect and can occur over a long period. Large cracks in the system will cause rapid leaks. But it’s more common for small, unnoticeable leaks to develop in the hoses connecting the AC components. Eventually, small leaks can cause the refrigerant pressure to drop significantly and prevent the AC from cooling your car.
Old hoses, worn o-rings, or a punctured evaporator can be to blame. The expert technicians at Ed Hicks Nissan can detect the leak source by injecting a special dye into the system to pinpoint the leak. Other ways to detect the leak source include inspecting for oily residue on the AC components and hoses.
Generally, the AC compressor can last a very long time. However, it can break down, causing your AC to blow warm instead of cold air.
The AC compressor is the system’s only moving part, so it’s more subject to wear than other parts.
You might notice other symptoms of a failing AC compressor:
Your compressor is run by the engine belt, which spins its compressor pulley. Since the compressor doesn’t always run (i.e., you turn off the AC), the pulley usually has a magnetic clutch that’s turned on/off as needed. If this clutch fails, the AC compressor won’t be able to rotate. However, you can’t conclude this from visual inspection alone. If your AC system is low on refrigerant, the compressor may stand still, appearing as if something’s wrong with it.
The AC condenser looks similar to your car’s radiator. It can be mounted in front of or to the side of the radiator. A bad condenser reduces the AC system’s efficiency, which could damage the AC compressor. If the condenser develops a crack, you’ll also lose refrigerant.
Since the condenser is mounted on the front of the car, debris, mud, insects, and rocks can clog its fins, reducing the refrigerant cooling efficiency. If your car AC starts cold and then gets warm, your condenser may be too clogged with debris.
Corrosion from street salts and moisture can damage and loosen the condenser fins, making the condenser structure shaky. Repetitive vibration can lead to micro cracks where tubes meet the condenser side tanks, causing refrigerant loss.
Your car may have separate radiator and condenser fans or one fan for both. Either way, if the condenser fan isn’t working properly, your AC may blow warm air. The condenser must be cooled. Otherwise, the refrigerant won’t be able to produce that beautiful breeze we all like!
Cooling fans can get damaged from road debris like plastic bags, rubber bits, leaves, and other contaminants the fan can suck in. Likewise, the fan motor can lose power from wear and tear, reducing the refrigerant cooling efficiency in the condenser.
Besides AC blowing hot air, you may notice these signs of failing condenser and radiator fans:
Numerous electrical issues could also prevent the cooling fans from working correctly. These are best left to professionals to diagnose. Our experts at Ed Hicks Nissan can find and fix the problem for you.
The AC filter captures allergens, pollutants, and other air contaminants from entering your AC system. But if it gets too clogged, it can also stop working. We recommend replacing the cabin air filter in accordance with your vehicle’s maintenance schedule or when it prevents the AC system from running smoothly. Regular maintenance is key to helping keep your AC system in top condition.
The expansion valve removes the pressure from the refrigerant, allowing it to enter the evaporator (inside the passenger’s cabin) with a reduced pressure (and temperature). If something is wrong with this valve, the evaporator won’t get a low-temperature refrigerant, causing your AC to blow warm air.
A bad expansion valve can also cause your AC to start cold but turn warm after a while. The system may even successfully regulate the refrigerant flow, causing the AC to cool again. However, you should get your vehicle to a mechanic soon to prevent further damage to the system.
Everything from the ECU to bad wiring and blown fuses could affect your AC system. The electrical system is deeply connected to the AC, so if something goes wrong, your AC could be blowing warm air.
Electrical problems can also indirectly affect the AC. For example, a faulty temperature sensor won’t communicate with the ECU to prompt the cooling fan to start. If the cooling fan doesn’t run, your condenser can’t cool down the refrigerant, leaving you sweltering inside the car.
It can be challenging to locate the electrical issue affecting your AC. Professional technicians can diagnose electric issues for you and replace any worn or faulty wiring or devices, breathing new life into your AC system.
We encourage folks from Rockport, Ingleside, Port Aransas, and other cities around Corpus Christi to visit us at Ed Hicks Nissan for AC service and repair. Our experienced team will get to the source of your AC woes and offer a service plan that will have you feeling the cool air breeze in your face in no time. Schedule your appointment today!
