Car AC Blowing Hot Air? Here's How to Fix It (2024)

Understanding the Causes

A quick understanding of how air conditioning works can help with understanding what the causes could be. When AC is turned on, refrigerant that flows through the system absorbs heat from your vehicle’s cabin where it’s removed and, through a series of parts and processes, the heat is released into the atmosphere before circulating back and repeating the process. There are several points where something can be wrong, causing warm air rather than cool:

• There isn’t sufficient airflow in the cabin. This could be a problem with a bad blower motor, but more commonly a plugged cabin air filter is the culprit.
• There isn’t enough refrigerant. The gas that circulates through the system can leak out, preventing it from working efficiently.
• The compressor may not be cycling. A clutch issue or a compressor failure can prevent the AC system from being able to disperse the heat the refrigerant has absorbed.
• The expansion valve is clogged. A blockage in the expansion valve could mean cooled refrigerant can’t circulate back to the cabin.
• The radiator is blocked. Debris blocking the condenser, mounted behind the radiator, could make it impossible for the heated refrigerant to cool effectively.
• There’s an electrical issue. A number of electrical connections could be loose or damaged, or a part like the HVAC control may not be working well.

If the air from the vents is blowing cool but not cold air, the airflow is weak, the vent temperature goes from hot to cold frequently, or you’re only getting warm air from the vents, it’s time to give your AC some attention.

DIY Diagnosis and Quick Fixes

Many AC problems can be identified on your own, and some can be remedied with a quick fix.

• First, check the cabin air filter condition and replace it if it’s dirty or clogged.
• Check that the heater fan is blowing. If it’s only blowing on high speed, the blower motor resistor might be faulty or a fuse might be blown.
• Clean off the radiator. If it’s plugged with debris like leaves, dirt, and bugs, wash it off to allow air to pass through it and the condenser.
• Check all the wiring connections for the AC system that you can access. There might be a loose connection at the AC compressor, for example. Check along the wires for rubs or cuts.
• Check the refrigerant level and top it up. Using a DIY refrigerant kit with a gauge, determine if the system is full or below full. Top up the refrigerant level according to the product’s instructions and check the vent temperatures again.

Routine Maintenance Tips

Routine maintenance is essential to ensure your car’s air conditioning system continues to blow cool air, especially during warmer months. A simple yet effective maintenance step is routinely checking and replacing the cabin air filter. A dirty or clogged filter can restrict airflow and reduce the system’s effectiveness.

Having your air conditioning system professionally inspected at least once a year can help identify potential issues before they lead to significant damage or inefficiency. This inspection should include checking the refrigerant levels and ensuring there are no leaks in the system. Regularly running the AC, even during cooler months, can also prevent seals from drying out and cracking, which can lead to leaks.

Furthermore, keeping the car’s radiator and condenser clean can prevent overheating and ensure the AC runs efficiently.

When to Seek Professional Help

If your DIY diagnosis doesn’t reveal the problem or you aren’t able to conclusively find what’s causing the problem, get a professional involved. It’s easy to spend a small fortune replacing parts as a guess, and you might still require a visit to the mechanic to get it fixed.

When you’re looking for a repair shop to take your car to, ensure that they have professional-grade equipment to perform AC repairs. Because R134a refrigerant is a controlled material, their technicians need to be certified to recover and recharge your system.

Related: How Much Does it Cost to Fix a Car AC?

Preventative Measures for a Cool Ride

To help avoid AC system problems, keep your engine bay clean, preventing dirt from accumulating on the condenser. As well, make a cabin air filter replacement an annual task right before summer arrives.

During winter months, use your AC to help defrost the windshield and condition your cabin more effectively. Along with being effective, it can also help you identify if there are issues that need to be addressed before it gets hot outside. If you determine the job is too big to tackle, check out our list of Preferred Shops in your area to help you complete the job.

When you need AC parts, your local AutoZone has them for you in stock, and from top brands including Duralast and more. We make it easy to get what you need with in-store and online shopping options.

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