Car Overheats When the AC Is On (Causes & How to Fix it)

If your car overheats while the air conditioning (AC) is on, it could be due to several reasons. Here we will learn the most common possible causes of why car overheats when the AC is on.

Although it’s normal for a few vehicle models to experience a slight increase in temperature when the AC compressor is on and the engine is operating, it should return to its regular temperature once the compressor turns off.

There are multiple reasons why your engine overheats when the AC is on, but a defective fan motor, fan switch, or engine cooling fan is one of the most prevalent reasons. Other factors that can contribute to overheating include clogged AC condenser fins, a faulty water pump, or a malfunctioning engine coolant sensor.

Even if the AC of your car is working efficiently to cool the interior of the car on a hot day, the engine could be experiencing issues that could cause the temperature gauge to rise.

If you notice your engine’s temperature gauge climbing while the AC is running, it’s important to understand the potential causes of the problem. This article provides information on the most common reasons why your car overheats while the AC is on.

Causes Of Car Overheats When AC is On

Your car overheating when the AC is on due to one or more below-given reasons:

• Bad Engine Coolant Sensor
• Faulty Fan
• Faulty Water Pump
• Overloaded AC Compressor 
• Increased Engine Load
• Blocked Water Condenser Fins 

1) Bad Engine Coolant Sensor

A faulty engine coolant temperature sensor is one of the major causes of the car overheating when the AC is on.

Your car’s engine coolant sensor plays a crucial role in monitoring the internal temperature of the vehicle engine and reporting it to the Powertrain Control Module (PCM). This information helps the PCM decide when to activate the engine cooling fan.

However, a faulty coolant sensor may give wrong temperature readings to the PCM, leading to a situation where the cooling fans fail to turn on at the appropriate time. This can ultimately cause your vehicle to overheat.

2) Faulty Cooling Fan

One of the most frequent reasons why your car overheats when the air conditioning system is on is due to malfunctioning engine fans.

Your vehicle engine contains multiple fans. These fans are responsible for adjusting their speed to cool the engine based on the car’s airflow. They are distinct from the fans that blow cool air onto the driver and passenger’s faces.

When the engine cooling fan becomes bad, or if the fan motor, fan switch, or fan blades are damaged, it can cause overheating.

Read More: Bad Radiator Fan Symptoms and Causes

3) Faulty Water Pump

A bad water pump is another potential reason for the car overheating while the AC is on.

The function of the water pump is to circulate a mixture of water and coolant throughout the engine, which helps maintain the internal operating temperature. When the water pump fails, the entire cooling system becomes ineffective, leaving your car interior dangerously hot.

4) Overloaded AC Compressor 

The compressor is one of the most important components of your car’s AC system. The main function of the AC compressor is to pressurize the refrigerant and utilize power from the engine’s output shaft to perform this job.

If the AC compressor malfunctions, it exerts a rotational load on the crankshaft, which can cause the engine to overheat.

5) Increased Engine Load

The engine of your vehicle has a limit beyond which it cannot operate. If you exceed this limit, your engine may overheat. An operating AC system puts an additional load on your engine, which can cause the temperature to rise if you’re also towing heavy loads up steep inclines.

If you have already eliminated any mechanical problems, it may be worthwhile to assess how you are using your car. It’s possible that you are expecting too much from your vehicle and pushing it beyond its capabilities.

6) Blocked Water Condenser Fins 

An overloaded AC condenser may lead to overheating; more commonly, the problem is with the condenser fins.

The AC condenser of your car is responsible for cooling off the hot refrigerant that circulates through the engine. However, the condenser fins can become clogged with dirt and debris, hindering the condenser’s efficiency. As a result, the coolant mixture cannot cool down sufficiently, and the engine overheats when the air conditioning system is turned on.

Read More: Limp Mode Symptoms and Causes

Parts of the Car Air Conditioning System

The air conditioning system has the following major parts:

• Cooling Fan
• Water Pump
• Radiator
• Thermostat

1) Cooling Fan

The cooling fan in your car adjusts its speed in response to the vehicle’s airflow and engine temperature. It ensures that the engine remains cool and prevents it from overheating.

When the interior of the vehicle becomes hotter than normal, the fan speed increases to cool the engine, and vice versa.

2) Water Pump

The water pump in cars is powered by a belt that is connected to the engine’s crankshaft. The water pump has the responsibility to properly supply coolant to the cooling system and has no impact on the engine’s oil lubrication, which is put in another oil sump.  

This pump includes a filter that the coolant passes through before entering the radiator.

The proper circulation of the engine coolant throughout the vehicle engine is maintained by the water pump that derives its power from the engine. This pump facilitates the movement of the fluid through the engine to keep it running smoothly.

3) Radiator

The radiator is one of the most important components of your car’s cooling system that ensures the proper cooling of the engine. It functions as a liquid-to-air heat exchanger and is comprised of tubes that receive liquid coolant from the water pump.

When the coolant mixture moves through the radiator, the air is blown across the coolant to lower its temperature before being circulated back into the engine.

4) Thermostat

The thermostat is also a crucial part of the cooling system that plays a role in regulating engine temperature. It senses changes in coolant temperature and adjusts the frequency at which the coolant system cycles on and off accordingly.

If the thermostat malfunctions, it can either open too quickly or remain closed for an extended period, which can cause the engine to overheat.

Read More: Bad Thermostat Symptoms and Causes

How to fix an overheating engine when the AC is on

If your engine is overheating while the AC is on, you need to replace or repair one or more below-given parts:

• Check cooling system
• Check refrigerant 
• Add more coolant 
• Check the radiator/AC condenser fan
• Service air conditioner
• Connect an OBD2 scanner

1) Check the Cooling System

If you suspect that your car’s engine is overheating, the first step is to inspect the cooling system. The cooling system contains multiple components, including the radiator and hoses.

To prevent overheating, ensure that the radiator is in good condition and not blocked, and the hoses shouldn’t be leaked or damaged.

If the cooling system appears to be functioning correctly, but the engine is still overheating, then you should properly inspect your radiator cap.

Steam rising from the radiator before it reaches the engine compartment’s top, especially while driving slowly with the heater on full blast, may indicate a faulty radiator cap that is stuck shut.

2) Check Coolant

To check coolant leaks in your car’s cooling system, follow these steps:

• You must utilize a flashlight to help illuminate the area around the radiator tank, which can be dark.
• Properly check your vehicle’s condenser and radiator for a wet spot, which may indicate damage and leakage.
• Check the radiator core for a leak.
• Properly check the lower and upper hose clamps on the radiator and tighten them properly if needed.
• Ensure that the radiator and condenser fins are in good condition.
• Check the oil dipstick to check for any signs of coolant leak into the engine.
• If you observe a leak, it’s crucial to have it repaired promptly. The cost of repairing or replacing a radiator or condenser is significantly less than that of an engine replacement.

3) Add More Coolant 

This issue can be easily resolved. It’s worth noting that insufficient coolant is the most common reason for engine overheating, so be sure to check the coolant levels in your car regularly.

Follow the below-given steps to add more coolant:

• Wait for the engine to cool down before checking the coolant level.
• Find the coolant reservoir, which is usually situated on the side or front of your engine under the hood.
• If your vehicle has a transparent reservoir, check the coolant level by looking at the markings on the side of the reservoir. These markings usually include a “Hot” and “Cold” line.
• In the case of the cold engine, the coolant level should be at or near the “Cold” line. If the level is below this mark, add more coolant to the reservoir.
• To add the coolant to the coolant reservoir, remove the cap and pour the coolant into the reservoir.

In addition to adding more coolant if the level is low, it’s crucial to check your cooling system for leaks. Your engine hoses, seals, and gaskets may wear out with time and cause fluid to leak from the system. Before adding more coolant, it’s essential to fix these leaks; otherwise, you’ll encounter the same issue later on.

4) Check the Radiator/AC Condenser Fan

To check if a blown fuse is causing a radiator fan to malfunction, follow these steps:

• First of all, you need to park your car in a safe place.
• Find the fuse box, which is usually located under the dashboard.
• Use a multimeter to measure Direct Current (DC) Voltage, and choose the appropriate range for the 12V circuit you want to test.
• Connect the negative lead of your multimeter to the negative terminal of your vehicle battery.
• Use the red lead of the multimeter to test the fuse contact for the radiator fan.
• If your reading is about 12V, it means that your fuse is functioning properly. However, if you get a 0V reading on one side of the fuse contact, it’s likely that your fuse is blown. A 0V reading on both contacts suggests that there’s no power coming to the fuse at all.

Note that besides a blown fuse, a radiator fan may also fail to work due to obstructions. To rule out this possibility, inspect the fan for debris that may be blocking it, and clean it as needed.

5) Service Air Conditioner

If your car overheats when the air conditioner is on, it’s important to have it serviced promptly. A professional service can identify and address potential causes such as a blocked radiator, low refrigerant or coolant levels, clogged condenser fins, and other related problems.

However, if these issues have been ruled out and your car still overheats when the AC is on, it’s time to investigate further.

6) Connect an OBD2 Scanner

Check the dashboard for warning lights, and use a compatible OBDII scanner to read any error codes that are displayed. Simply plug the scanner into the port located under the steering wheel to access this information. 

Once you’ve obtained the error codes, consult your vehicle manufacturer’s manual and fix the underlying issues. With the right information, you can quickly identify and address the root cause of the problem and avoid any further damage to your car’s systems.

FAQ Section

Can an overcharged AC cause an overheating engine?

When your AC is overcharged, it may lead to the compressor failure. An issue with the compressor puts extra load on the engine, which, if left unaddressed, can eventually cause the engine to overheat due to increased stress.

Can a faulty AC compressor cause a car to overheat?

The compressor itself does not directly cause engine overheating, but the improper operation of the compressor clutch can place additional strain on the engine, potentially leading to overheating.

Does the car AC make the engine hotter?

It’s important to note that the air conditioner imposes extra stress on the engine. If your engine is already susceptible to overheating, the increased workload from the air conditioner may push it beyond its limits. In certain situations, simply turning off the AC may prevent engine overheating.

What are the symptoms of a bad AC compressor?

• Engine overheating
• Insufficient cooling
• AC system leaks
• Electrical issues
• Excessive noise
• Frequent cycling

Should the AC be on or off if the car is overheating?

If you are driving on an open road and observe that the vehicle is experiencing overheating, your initial step should be to switch off your AC. Operating the air conditioning exerts an additional strain on your engine, exacerbating the issue.

Read More

• Bad Water Pump Symptoms and Causes
• How To Fix Radiator Leaks?
• Causes of Oil in Coolant
• Engine Oil Color Chart