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Home / Symptoms / Overheating AC

Four common causes for a vehicle overheating after turning the A/C on and their related parts.

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Is Your Car Overheating When You Turn The AC on?

The car is overheating after turning the air conditioning on because of a faulty coolant temperature sensor, clogged radiator, and condenser fins. Less commonly, it can be an issue with the condenser fan relay or fan control module.

Consider having a skilled professional diagnose and fix the car's air conditioning issue. This approach helps keep your car in excellent condition, ensuring your safety. Remember, neglecting a seemingly minor issue could cause more significant problems in the future, which could have been avoided with timely attention and maintenance.

Watch out: A car AC overheating can be a serious issue involving different electrical parts, meaning you need to check it quickly. Failure to do so could lead to a car overheat, safety hazards, and costly repairs.

Let's Get To The Bottom Of It!

Does the engine overheats even if the temperature gauge says otherwise?

The temperature-sending unit is a part of your car's engine that tells the engine control module (ECM) how hot the engine is. It's located in the water passages before the thermostat and works with the coolant temperature sensor to regulate the air-fuel mixture. The temperature sender also sends a signal to the instrument cluster, which helps turn on the cooling fans when the engine gets too hot. But if the temperature sensor reads the wrong temperature, the engine might overheat without the temperature gauge indicating its actual value.

Is the temperature gauge continuously rising as you put more load in the engine?

The radiator is crucial to your car's cooling system. It has a storage tank with fins attached to each side of its core. If the cooling system is neglected, particles can build up and clog the radiator cores, restricting the coolant flow. If this happens, the coolant cannot go through the cores and dissipate heat, causing some cores to remain cooler than others. This can be seen with a thermal imager.

Is your AC starting cold and then gradually getting warmer?

The condenser is a part of the air conditioning system that sits before the radiator. Its job is to help remove heat from the freon and coolant by allowing air to flow across it. When the cooling fan turns on, it helps pull this air through the condenser and radiator to cool everything down. However, if it fails, it can diminish airflow. The AC and engine temperature can rise and cause problems if there isn't enough airflow.

Do you hear a rubbing noise from the cooling fans when you turn the AC?

The cooling fans help to cool down the engine and the air conditioning system by moving air across the radiator and condenser. If the bearings in the cooling fan motor wear down, the fan can rub each other, make noise and cause damage to the fan shroud.

Is the AC only cooling the cabin when you drive at highway speeds?

The condenser fan draws a lot of power and is controlled by a module using a relay. The contacts in the relay can get damaged due to the high current draw of the fan motor, preventing voltage from passing through and turning on the fans. The improved airflow when driving at highway speeds allows the condenser and radiator to keep the engine cool. Therefore, the air conditioning works appropriately through natural means.

Is the car's AC not working and displaying a "check engine" light on its dashboard?

Modern vehicles use a module to control engine fan speeds and maintain proper engine and air conditioning temperatures. If the module malfunctions, the engine control module will detect it, turn on the check engine light, and disable the AC system to prevent the engine from overheating.

The most common causes for a vehicle’s AC overheating

The most common causes for the car’s air conditioning overheating:

Clogged radiator: The radiator is a rectangular tank in your vehicle's front, exactly behind the front bumper. This tank cools your car down by sending cold coolant to various systems, including the AC. However, if the radiator is faulty or clogged, the coolant might not reach the AC, resulting in a bad air conditioning performance.
Clogged condenser fins: The condenser fins attach themselves to the condenser, a vital component that lowers the temperature of refrigerant gas inside your air conditioning. The fins are needed to help your AC have proper airflow and low temperatures to cool the air inside the cabin. If these fins become faulty or clogged, the temperature may rise.
Faulty condenser fan relay: A relay is an electrical switch that sends power toward the condenser fin, making it activate. If the relay is faulty due to electrical problems, the condenser fan, which is essential to keep airflow and low temperatures inside the air conditioner, stops working. Consequently, the AC malfunctions.
Faulty fan control module: The fan control module is a smart electrical "brain" that has built-in software so it can make "calculations" to control the fans inside the air conditioning system. These calculations help these fans adjust to the vehicle's current temperature and the driver's AC settings. However, if the module is faulty, fans might malfunction, reducing AC performance.
Faulty coolant temperature sensor: The coolant temperature sensor reads the temperature of the coolant inside the engine, helping the engine unit decide if it's time to switch coolant to avoid overheating. However, if the coolant temperature sensor fails, the engine might start overheating since it's not detecting a rise in temperature levels, resulting in hot air from the AC.
Faulty cooling fans: Cooling fans are vital to keep the AC system's airflow healthy and proper, ensuring cool temperatures. If the fans stop working, airflow is lost, and the vents start blowing weak air. Consequently, AC internal components start compensating and overstressing, becoming faulty and leading to malfunctions.

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Frequently Asked Questions

Does the engine overheats even if the temperature gauge says otherwise?

The temperature-sending unit is a part of your car's engine that tells the engine control module (ECM) how hot the engine is. It's located in the water passages before the thermostat and works with the coolant temperature sensor to regulate the air-fuel mixture. The temperature sender also sends a signal to the instrument cluster, which helps turn on the cooling fans when the engine gets too hot. But if the temperature sensor reads the wrong temperature, the engine might overheat without the temperature gauge indicating its actual value.
Is the temperature gauge continuously rising as you put more load in the engine?

The radiator is crucial to your car's cooling system. It has a storage tank with fins attached to each side of its core. If the cooling system is neglected, particles can build up and clog the radiator cores, restricting the coolant flow. If this happens, the coolant cannot go through the cores and dissipate heat, causing some cores to remain cooler than others. This can be seen with a thermal imager.
Is your AC starting cold and then gradually getting warmer?

The condenser is a part of the air conditioning system that sits before the radiator. Its job is to help remove heat from the freon and coolant by allowing air to flow across it. When the cooling fan turns on, it helps pull this air through the condenser and radiator to cool everything down. However, if it fails, it can diminish airflow. The AC and engine temperature can rise and cause problems if there isn't enough airflow.
Do you hear a rubbing noise from the cooling fans when you turn the AC?

The cooling fans help to cool down the engine and the air conditioning system by moving air across the radiator and condenser. If the bearings in the cooling fan motor wear down, the fan can rub each other, make noise and cause damage to the fan shroud.
Is the AC only cooling the cabin when you drive at highway speeds?

The condenser fan draws a lot of power and is controlled by a module using a relay. The contacts in the relay can get damaged due to the high current draw of the fan motor, preventing voltage from passing through and turning on the fans. The improved airflow when driving at highway speeds allows the condenser and radiator to keep the engine cool. Therefore, the air conditioning works appropriately through natural means.
Is the car's AC not working and displaying a "check engine" light on its dashboard?

Modern vehicles use a module to control engine fan speeds and maintain proper engine and air conditioning temperatures. If the module malfunctions, the engine control module will detect it, turn on the check engine light, and disable the AC system to prevent the engine from overheating.

Typical fixes to address the cause(s)

These are typical processes and repair services that fix a check engine light issue

The most common cause: Clogged radiator

The most common reason for a car’s air conditioning to start overheating instead of cooling the air is due to a clogged radiator. The radiator needs to have all its tubes, hoses, and internal channels free of debris. This is because the radiator needs to send coolant properly to many systems like the engine and air conditioning. If the radiator gets clogged, the coolant won't get as far as it needs, resulting in bad cooling and possible overheating.

Symptoms it causes: Apart from the overheating AC you might notice engine overheating, humming noises, and coolant leaks.
High risk of priority: A clogged radiator might lead to engine overheating. If the engine overheats, your vehicle won't resist the high temperatures and might break down in longer and more demanding rides.

How exactly does the radiator clog up?

The radiator depends on many channels, tubes, hoses, and internal chambers to properly send and manage coolant inside your vehicle. Unfortunately, the radiator can get clogged with debris, mineral deposits, rust, or sludge that accumulates over time.

Go safe: Ask for a mechanic to inspect your vehicle’s cooling system to investigate if the radiator is faulty due to surrounding components and if there’s further damage to check out. Many shops do transparent vehicle inspections and lay out your options after investigating your vehicle’s conditions.

What’s a vehicle inspection? It’s “detective work” on your vehicle, checking its systems to see if anything prevents the car from working as expected. In this case, mechanics examine different parts of your vehicle to track if anything is causing the radiator to clog up. They’ll also check the condition of components during their inspection, noting which are causing the problem and which got affected by it, recommending to replace them in order of priority.

Transparency example in a clogged radiator service

A cooling system inspection is the most transparent process to understand why your vehicle’s radiator is faulty. This is because many components surrounding the radiator, cooling hoses, and AC compressor can have a say in the issue, indicating the real culprits that caused it all.

Let’s read an example of how this kind of inspection helps to service a clogged radiator.

A customer dropped off their vehicle complaining about the temperature gauge rising while using the air conditioner. They mentioned that the temperature gauge rose to the red zone while driving up steep hills, and the air conditioner stopped working; this was a common occurrence. However, the vehicle's temperature gauge returned to normal while going downhill, and the air conditioner worked again.

During the test drive, the technician didn't notice any issues related to the customer's concern. However, they did see that the check engine light was on. Then, during the vehicle health inspection, the technician observed that the coolant was cloudy, and small chunks of particulates were on the gas bottle's side.

After scanning for vehicle codes, the technician found a P0217 engine in an over-temperature condition. The customer authorized additional diagnostics, and the technician began warming up the engine in the service bay to get the temperature to rise.

The engine cooling fans were at 220°, but the temperature continued to climb to 228°. The technician tested the airflow across the condenser and radiator cores by holding a rag before the fan, revealing enough airflow to hold up the rag.

The technician used a thermal imaging scanner to verify if the temperature-sending unit was correct. They discovered the temperature was within one degree of the live data readout. The technician then used the scanner to check the radiator and found that the coolant flow was restricted in the bottom half of the radiator, indicating clogged radiator cores.

The technician recommends replacing the radiator and doing a cooling system flush to eliminate particles in the engine block and hoses.

Clogged radiator

In this case, the mechanic put the “Immediate Action” tag on the radiator and a coolant system flush.

Similar Symptoms

Below are just a few examples of typical Symptoms and Fixes your car might be experiencing

Four common causes for an AC not cooling the vehicle and their related parts.