Car AC Turns Off At Wide Open Throttle: Fixed!

Car air conditioning (AC) is an essential part of the driving experience. It keeps you cool and comfortable, especially during those hot and humid summer days. However, it’s common for the AC to turn off at wide open throttle (WOT). You would not want to let this overheating issue ruin your summer fun. With a bit of knowledge and troubleshooting, you can get your car’s air conditioner running smoothly again.

So, why does car AC turn off at wide open throttle? Generally, it’s a safety feature that kicks in whenever the engine RPMs exceed a certain point so that pressure inside AC system does not rise too high. Furthermore, your car’s computer is designed to shut off the AC when the engine is running at a high speed. This is so that more power can be diverted to the engine and the car can run more efficiently.

Does AC Turn Off At Full Throttle?

Car AC system does shut off under full throttle, but for a good reason. The ECM senses when full throttle is achieved and it will automatically shut off the AC compressor under these conditions. This is done to allow more power to be available to the wheels, as the assumption is that at full throttle the driver is wanting maximum acceleration.

Basically, when you press the accelerator, the engine must work harder to move the vehicle forward, which requires more fuel and power. To provide this extra power, the air conditioning compressor is turned off to reduce the load on the engine, and the extra power is used to provide the vehicle with additional acceleration.

The good news is that the AC system will automatically turn back on once the ECM senses that full throttle has been released. This ensures that the car owner gets the best of both worlds, maximum performance, and comfort. 

Once you’re done accelerating your vehicle and cruising it at a steady speed, the AC will turn back on.

What Is Wide Open Throttle?

Wide Open Throttle (WOT) is when your engine is running at full throttle, meaning that the throttle plate is fully open and the engine is running at maximum speed. This is in contrast to a “closed throttle” where the throttle plate is closed and the engine is running at idle speed. WOT is usually achieved by pressing the accelerator pedal to the floor and revving the engine to reach its maximum RPM.

Using Wide Open Throttle can help you gain a better understanding of your vehicle’s performance. It can also help you troubleshoot any engine or performance issues and can help you diagnose any problems you may be having with your car. WOT is also a great way to test the limits of your vehicle’s power and performance. 

WOT should not be used while driving on the street, as it can be dangerous and can cause the car to lose control. It is also not recommended for daily driving, as it uses more fuel and can cause unnecessary strain on the engine. 

How Does Car AC Compressor Turns?

Many people have a wrong perception that AC compressor always spins as long as the engine is running. But, that’s not true.

The AC compressor is the heart of your car’s air conditioning system. It is a pump driven by a belt connected to the engine’s crankshaft. The AC compressor compresses the refrigerant gas, which is then passed through the condenser, evaporator and expansion valve. This process cools the air that circulates inside the vehicle. 

The car’s AC compressor turns with the help of a serpentine belt that transmits power from the engine’s crankshaft to the AC compressor. The serpentine belt is a long, looped belt, made of rubber and metal, that is connected to all the pulleys in the engine including the AC compressor pulley. 

Here are the basic components of the car AC compressor system:

  • AC Compressor Pulley: This is the part of the compressor that is driven by the serpentine belt.
  • Magnetic Coil: This is the part of the compressor that engages the AC compressor clutch with the pulley.
  • AC Compressor Clutch: This is the part of the compressor that connects the pulley to the compressor, allowing it to turn.

You can watch the following Youtube video to understand the operation of an AC compressor:

Furthermore, I have written a detailed guide on car AC compressor engages and disengages intermittently to learn more.

How Does Throttle Control Car AC?

throttle body demonstration

The throttle controls the opening and closing of the car AC by sending the signals of the position of the butterfly valve in the throttle body.

The accelerator pedal is directly linked to the throttle body. The throttle valve is opened based on the position of the accelerator pedal. In an electronic throttle body, the accelerator pedal has sensors that send signals to the ECU so that it can control the throttle body.

If the throttle body is mechanical, it is connected to the accelerator pedal through a spring mechanism.

On the throttle body, you’ll see throttle position sensors (TPS) that send signals of the throttle valve position to the ECU. So, when the butterfly valve of a throttle body is fully opened at WOT, TPS sends its position signals to the ECU so that it can take necessary actions, such as disengaging the AC compressor clutch and turning off the AC.

Causes Of Car AC Turning Off At Wide Open Throttle

1. Too High Pressure In the AC System

High engine speeds are exciting when driving a car, but if the air conditioning system is failing to keep you cool, the thrill is gone. When your car’s AC turns off at wide open throttle, the problem is likely related to the pressure in the system. 

The compressor in your car’s AC system is driven by the engine. As the engine revs increase, so does the compressor speed. With this increase in compressor speed, the pressure of the refrigerant also increases. 

A high-pressure switch is installed in the AC system to protect it from excessive pressure. This switch shuts off the compressor when the high-side pressure reaches a certain level. So, if the system pressure is too high, it will cause the AC to turn off when the engine speed is increased above a certain limit to prevent the system from damage.

A scientific study has also been conducted in which the effect of AC compressor speed on the discharge pressure of refrigerant has been studied. The output of this study in the form of a graph is shown below:

effect of ac compressor speed on the discharge pressure of refrigerant

Source: https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=2469&context=iracc

Apart from the compressor RPM, the pressure inside the AC system can also readily increase due to blockage in the condenser, accumulator or orifice.

The hot, pressurized refrigerant passes through the condenser, where the heat is released into the atmosphere and the refrigerant is cooled. If the condenser is plugged up with debris and dirt, the compressor has to work hard to push the refrigerant. So, the refrigerant pressure increases.

2. Provide Full Power To The Wheels

The engine’s crankshaft supplies power to the AC compressor pulley via a serpentine belt. On the other hand, the engine’s crankshaft is also connected to the transmission to provide power to the wheels. 

When the car is at wide open throttle, the engine is working at maximum power and is sending most of the power to the transmission to power the wheels. This leaves less power for the AC compressor to work, causing the AC to turn off.

When the car is no longer at wide open throttle, the engine is no longer working at maximum power and has more power to send to the AC compressor. This results in the AC compressor working effectively and cooling the cabin. 

You can further read about it in my guide on car loses power and acceleration when AC is on.

3. Problem With Vacuum Check Valve

Keep in mind that the vacuum produced by the engine is minimum at the wide-open throttle and maximum at idle. The reason is that when the butterfly valve of a throttle body is fully opened at WOT to allow more air to enter the engine. At low engine RPMs, the vacuum continues to operate in the vacuum reservoir.

If the airflow from the AC vents stops and switches to the windshield, it means that there is a problem with the vacuum check valve.

Cars having manual AC have vents controlled by the engine’s vacuum. The vacuum produced by the engine’s air intake is responsible for controlling the opening and closing of vents’ flaps through vacuum-operated actuators.

The flaps that open and close the car AC vents are pulled shut by springs when their actuators are shut off.

In the engine, there is a vacuum check valve that closes when the vacuum is minimum at full throttle so that it prevents backflow of air through the vacuum line and the flaps of AC vents continue to operate at WOT.

From the following schematic diagram, you can understand the routing of vacuum lines in AC system:

schematic diagram of car ac vacuum system

Now, the default setting of the AC airflow is through the dash vents. If the vacuum drops, the airflow will shift to the windshield vents. This is what the vacuum check valve prevents, and allows airflow through dash vents when the engine is under load at wide open throttle.

So, if there is no airflow from AC vents at wide open throttle, you should check the vacuum check valve and any vacuum leaks in the AC system through vacuum hoses.

I have also attached the below Youtube video for a better understanding: