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Home / Symptoms / Overheating AC

Hey, Why Is My Car Overheating When I Turn The AC On?

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Four common causes for a vehicle overheating after turning the A/C on and their related parts.
If the cooling system of your vehicle is not operating to maximum performance, the air conditioning system will add additional heat to the front of the radiator and add extra load to the engine. When the AC is running, this extra heat and load will cause a marginal cooling system not to pull enough heat away from the engine and cause it to overheat.

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.

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.

Consider the assistance of a skilled professional to diagnose and fix the car 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.

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.

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Vehicle Health Inspection Proof

Explore the following typical inspection results that show a potential cause for the symptom and select the one you believe is similar to your vehicle's issue.

Clogged radiator

The proof image shows the thermal image of the radiator. The cool area indicates the clogged cores, while the brighter spot shows good coolant flow.

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 condenser fins

The proof image showed that with the front bumper removed, all the fins on the AC condenser were plugged, causing a malfunction over time.

A customer brought in their vehicle, reporting an issue with the air conditioner. The air conditioner worked fine initially, but it seemed to lose its cooling power as time passed.

During the initial test drive, the technician didn't notice anything wrong with the air conditioner, but by the time they returned to the service bay, the AC was barely working.

After a vehicle health inspection, the technician found nothing related to the customer's concern. However, they authorized additional diagnostics, so they hooked up an AC machine to the vehicle and turned it on while idling in the service bay.

The cooling fans immediately came on, and the pressure in the air conditioning system was normal. But as the AC continued to run, the "high" side pressure increased significantly, running 75 to 100 PSI higher than usual.

To check for airflow problems, the technician put a rag in front of the condenser, but the rag remained still. Then, they found that the condenser was almost entirely blocked with debris. Therefore, the front bumper must be removed to access the condenser fins, fan, and radiator. After cleaning out the system, the AC would be tested for performance.

Faulty condenser fan relay

The proof image shows the location of the failed high-speed fan relay.

A customer dropped off their vehicle and reported the air conditioner was not working well when driving slowly or idling. However, they noticed that the air conditioner started improving when they got highway speeds.

During a test drive, the technician confirmed the air conditioner was not cooling well when stopping the vehicle at a stoplight. Moreover, during the vehicle health inspection, the technician found nothing related to the customer's concern.

Because of this, the technician needed additional diagnostics, which required the customer's authorization, which they granted. The technician hooked up the air conditioning machine to the vehicle and turned on the air conditioner. They noticed that the condenser kicker fan was not engaging.

To investigate further, the technician used a scanner to confirm that the module commanded the fan to turn on. They discovered that the body control module was sending proper signals.

The technician then used the scanner while commanding the condenser fan and tested the wiring for voltage. Unfortunately, there was no voltage detected in the fan wiring. So, the technician shifted their attention to the fan relay.

In this context, the relay is an electrical component that controls the operation of the high-speed fan in the air conditioning system. It acts as a switch that allows electrical current to flow to the fan when the air conditioner is turned on.

The technician removed the high-speed fan relay and confirmed it had voltage. They then substituted it for a different relay and found that the fans came on, proving that the relay was defective and needed replacing.

Faulty fan control module

The proof image shows the location of the failed fan module, which caused the check engine light to come on and prevented the cooling fans from operating correctly.

A customer dropped off their vehicle and reported that the air conditioner was not working. They also mentioned that the "check engine" light was on the dashboard.

During a test drive, the technician confirmed the client's concerns and suspected a potential issue with the vehicle's cooling system.

During a vehicle health inspection, the technician found nothing related to the customer's concerns. However, they performed a vehicle code scan and found a p0480 code indicating a malfunctioning cooling fan (one) control circuit. So, the issue was fan-related and about electrical functionality.

To investigate further, the technician needed additional diagnostics, which the customer authorized. They used a vehicle-specific scanner to verify that the p0480 code was still present and then attempted to operate the fan with the bidirectional controls on the scanner. Unfortunately, the module would not engage the fans, indicating a potential issue with the fan module.

To verify this, the technician checked the power and ground going to the module and jump-started the cooling fan with power and ground. The fan operated correctly, proving the module was defective and needed replacing.

Faulty coolant temperature sensor

The proof image shows the failing coolant temperature sensor located in the water jacket. Replacing this sensor should fix the problem with the air conditioner and the engine's cooling system leak.

A customer brought in their vehicle, concerned because they heard a gurgling noise from the engine and saw coolant leaking out of the overflow bottle. They also mentioned that their air conditioner stopped working before the gurgling noise started. In addition, they did not notice the temperature gauge showing any issues.

During a test drive, the technician did not notice any issues with the customer's concerns. However, during a vehicle health inspection, the technician noticed the coolant was low, but nothing related to the customer's problems.

The technician requested authorization for additional diagnostics, and the customer agreed. The technician used a specialized scanner to check for error codes, but none were present.

They then ran the vehicle with the air conditioner on high for about 30 minutes, using an infrared thermal scanner to check the water passages around the temperature sender. Finally, they compared the readings from the scanner to the live data on the scanner, which showed a temperature of 195°.

However, the infrared thermal scanner showed that the temperature on the water jacket had increased to 225°, and the cooling fans did not come on. This confirmed a defective engine coolant sensor that needed to be replaced.

Faulty cooling fans

The proof image shows where the engine cooling fan blades hit the shroud due to the motor bearing failure.

A customer brought in their vehicle, mentioning that the air conditioning wasn't working correctly. They reported that whenever they turned it on, they heard a loud scraping noise from the front of the engine.

During the test drive, the technician heard a ticking, scraping noise from the front of the vehicle when turning on the air conditioning. However, during the vehicle health inspection, the technician didn't notice anything about the customer's concern.

To investigate the noise, the technician turned on the AC and ran the vehicle in the service bay. The noise was found to be coming from the cooling fan motor. The technician then turned off the car and waited for the fan to stop.

After that, the technician manually pushed the fan blade and discovered the motor bearings were loose and damaged. This caused the coolant system fan blades to rub against the shroud, creating a scraping noise. Therefore, the cooling fan motor and the air filter needs to be replaced.

Typical Fixes to Address the Cause(s)

The following chapters bases themselves on experiences from our auto repair shop; we'll describe related problems' causes and fixes.

Sometimes a problem is more challenging to describe than it initially looked like. If you are not sure your problem is described by this article, please find below similar vehicle symptoms, which might describe better the issue you are experiencing.

Vehicle Symptoms

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

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The air conditioner isnrsquot working because of a faulty compressor c...
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Four common causes for a vehicle A/C working inconsistently and their related parts.

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Itrsquos only working sometimes because the cabin air filter is too di...
Four common causes for a vehicle overheating after turning the A/C on and their related parts.

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The vinegar smell is probably due to moldy substances built up in the ...

Typical Fixes Pages