Car Engine Loses Power and Acceleration When AC Is On: 7 Potential Causes

It’s a hot summer day, and you turn on the AC in your car to stay cool. But as soon as you do, you notice your “car loses power and acceleration when ac is on“. The engine seems to struggle, almost like it can’t handle the extra load of the AC compressor

In this guide, we’ll look at some potential causes and solutions for when your car loses power and struggles to accelerate when the AC is on.

First off, the AC puts additional strain on the engine, reducing its power and acceleration. So, the engine has to generate more power to overcome the strain exerted by the AC.

So, why car loses power when ac is on? When a car loses power with the AC on, several issues could be responsible: a clogged air filter restricting engine’s airflow, a blocked condenser, an improperly tensioned serpentine belt, or a faulty fuel pressure regulator. A malfunctioning alternator, a slack timing chain/belt leading to incomplete combustion, or a dirty throttle body can also cause this power loss. Regular checks and maintenance can help ensure optimal performance.

Bonus Read: What happens if AC is left on while car is parked and engine is running

Does Ac Affect Engine Power?

When the AC is running, the engine has to work harder to power the compressor and condenser fan, which means it has less power to accelerate the car. This means that acceleration might be slightly reduced when the AC is running. However, the effect is usually not noticeable and wouldn’t greatly affect the performance of your car. 

The main effect of having an air conditioner in your car is on your fuel economy. Having an AC in your car uses up engine power, which means more fuel is being used. This is because the compressor needs energy to run, and this energy is taken from the engine. The result is that fuel usage increases slightly when the AC is running, as more power is being used. 

Note: Keep in mind that the AC condenser fan and AC blower run from the car battery while the AC compressor runs from the engine crankshaft which supplies power through the serpentine belt to the AC compressor pulley.

However, there is a magnetic coil inside the AC compressor clutch that gets 12V from the battery to energize itself and engage A/C clutch drive plate inward with the pulley. AC compressor clutch engages and disengages with the pulley to maintain

Must Read: How to reduce AC load on engine

Also, note that some cars also tend to turn off AC compressor under hard acceleration to ease off the extra strain on the engine, and to reduce the power loss.

Causes Of Car Engine Losing Power and Acceleration While AC Is On

If you experience a sudden drop in power and acceleration when you turn on the air conditioning (AC) in your car, you may be concerned and confused. There could be several possible causes of this problem, so it’s important to take some time to identify the source of the issue.

Let’s take a look at some of the other potential causes of a car engine losing power and acceleration while AC is on:

1. Clogged A/C Condenser

clogged car ac condenser

A clogged A/C condenser can cause your car to lose power and struggle during acceleration while AC is on. AC condenser does not directly affect the engine’s performance. Instead, it affects the efficiency of your car AC, due to which your engine’s performance is also affected.

Now, let’s explain how a clogged A/C condenser can indirectly impact the performance of your engine.

A clogged AC condenser can cause a car to lose power and acceleration while the AC is on because the condenser is responsible for dissipating heat from the refrigerant in the AC system.

When the condenser becomes clogged with dirt, debris, or other contaminants, it becomes less efficient at dissipating the heat of the refrigerant.

Furthermore, it could also cause excessive pressure of refrigerant in the AC system. As a result, the refrigerant in the system can become overheated, which can cause the AC compressor to work harder and use more power. Due to this reason, the RPM and the power of your car is reduced while driving when you turn on the AC.

Must Read: Car sputtering and shaking when ac is on

2. Bad Fuel Pressure Regulator

A fuel pressure regulator is a device that is used to regulate the pressure in the fuel rail of a vehicle. It is responsible for ensuring that the pressure in the fuel rail is at the correct level, which is necessary for proper engine performance.

The pressure regulator is typically located at the fuel rail, which is the part of the fuel system that supplies fuel to the engine. 

When the engine is idle, less power is needed. As a result, the fuel pressure regulator returns extra fuel to the tank to maintain fuel pressure.

As you increase speed and press the gas pedal, more air enters the engine through air intake system.

As a result, the fuel pressure regulator closes the opening to the fuel tank as more fuel is needed by fuel injectors to maintain desired air-fuel mixture.

A bad fuel pressure regulator can be a major issue for your vehicle. Low fuel pressure can cause a variety of problems, including poor performance and decreased fuel economy.

Other symptoms of a bad fuel pressure regulator include a rough idle, hard starting, and stalling.

Also, the throttle body may get dirty frequently due to a bad fuel pressure regulator. This happens when the diaphragm inside a fuel pressure regulator ruptures, due to which fuel sucks into the throttle body.

If a fuel pressure regulator becomes bad, the air-fuel mixture will become lean. As a result, inefficient combustion will take place, and the engine couldn’t produce enough power. So, when you turn on AC in this condition, the extra load on the engine will significantly reduce the power and acceleration of your vehicle.

To check if the fuel pressure regulator is bad, you need to first measure the fuel pressure using the fuel pressure gauge kit. The optimum fuel rail pressure depends on the engine.

3. Clogged Air Filter

An engine air filter is a part of your car’s air intake system. It is a paper, foam, or fabric filter that prevents debris, dirt, and other particles from entering your engine and damaging the cylinders. 

The air filter plays a crucial role in the combustion process of your engine. When the air filter becomes clogged, it restricts the amount of air that is allowed to enter the combustion chamber.

When the air intake is restricted, there is less oxygen available for the fuel to combust, leading to a decrease in power and acceleration.

A bad air filter looks dark in color or gey. A dirty air filter is often overlooked. It is essential to have it changed every 20,000 miles or 1 year to maintain the engine’s performance.

Must Read: Car loses power when turning corners

3. Dirty Throttle Body

bad throttle body

A throttle body is a part of the air intake system of a car’s engine. It controls the amount of air that goes into the engine and helps to regulate the speed and power produced by the car engine.

When a throttle body gets clogged with dirt, it can cause the car to lose power and acceleration when the air conditioning (AC) is on. This is because the air intake is restricted, which reduces the amount of air that goes into the engine.

It disturbs the air-fuel mixture, due to which the engine is not able to produce enough power to maintain the speed of the car, causing it to slow down. 

A dirty throttle body can be caused by a number of things. The most common cause is a build-up of dirt and debris in the air intake system.

This build-up can be caused by a number of things, such as a dirty air filter or a leaky air intake hose. The dirt and grime can then get mixed with the lubricating oil and form a sticky substance that affects the throttle body’s operation.

Now when there are sticky dirt and carbon deposits in the throttle body, they will prevent the butterfly valve of the throttle body to move freely, which will disturb airflow to the engine.

You should use this throttle body cleaner to clean the throttle body. Make sure that the throttle plate of a throttle body is not binding when you try to move it with your finger.

4. Locked Up AC Compressor

AC compressor of car

When it comes to your car, nothing is more important than power and acceleration. It’s what gets you from point A to point B, and the last thing you want is to experience a decrease in these areas when you turn on your air conditioning (AC). Unfortunately, this can be the case if your AC compressor intermittently seizes while running. 

A compressor is an integral part of an AC system, and it is responsible for pressurizing the refrigerant and then directing it to the evaporator.

The compressor is driven by a pulley, which is then connected to the engine by a belt. This belt is powered by the engine to run the compressor, and when it fails, your AC will not work. 

When the compressor seizes up, it puts a strain on the engine, causing it to lose power and struggle for acceleration.

How AC Compressor Siezes?

When the AC compressor seizes, it is usually caused by a lack of lubrication or wear and tear.

As the compressor is continually working to compress the air, it needs to be lubricated properly to ensure it works properly. If the compressor isn’t properly lubricated, it can cause the compressor to wear out or seize. 

Another common cause of a seized compressor is a faulty compressor clutch. The clutch is responsible for connecting the AC compressor to the engine and can become worn down over time. When this happens, the clutch may not be able to fully engage the compressor, causing it to seize. 

How to spot the issue?

If the AC compressor is partially seizing, it could drag the engine down, due to which the serpentine belt may show signs of glazing or similar effects of heat caused by the belt having to work harder.

The serpentine belt may begin to lose its strength and elasticity, or it may even melt from all the chaffing and rubbing.

If you notice any glazing or melted spots on the belt, it’s a definite sign that your AC compressor is partially seized.

So, in that case, you have to check:

  • AC compressor
  • Compressor clutch
  • Compressor pulley

Now, take the serpentine belt off the compressor pulley, and rotate the inner part of the compressor (shaft) by hand using an 8mm socket. It should rotate freely.

turn ac compressor by hand to check if it is seized or not

Now, try wiggling it and see if there is any excessive play. Similarly, also check the compressor pulley and compressor clutch. There should not have any play in the AC clutch.

5. Serpentine Belt Slipping

serpentine belt

A serpentine belt is an integral part of any car’s engine. It’s responsible for connecting the crankshaft to the various components in the car, such as the alternator, power steering, water pump, and air conditioning compressor.

Serpentine belts are designed to last for a long time, but eventually, they will wear out and need to be replaced. When this happens, the belt will start to slip and you will begin to notice certain signs. These include:

  • A screeching sound when the engine is running
  • Squeaking noises as the belt pass the pulley
  • A burning rubber smell
  • A decrease in power and acceleration

You need to check the following aspects:

  • Pulleys of the engine components, over which the belt passes, may not rotate freely. You should especially check the alternator pulley and compressor pulley. These pulleys should rotate freely.
  • The tensioner and idler pulley might have a play in them. The Idler pulley of the serpentine belt should be fully tight.
  • The belt may not fit all pulleys snugly.
  • There might be more than 1-2cm slack in the serpentine belt.

6. Bad Alternator

Alternators are an essential part of a car’s electrical system. They produce power to start the engine, keep it running, and charge the car battery.

When the alternator is failing, it can’t provide enough power to keep the engine running and the car’s electrical system working properly. This can cause a number of problems, including a loss of power and acceleration.

The function of the alternator is to continously charge the engine’s battery while driving, and the battery supplies current to the engine control module and different sensors for optimal performance.

Fortunately, there are warning signs that can alert you to a failing alternator. If you notice any of the following, it’s a good idea to get your alternator checked or replaced. 

  • Dimming or flickering headlights
  • Slow-starting or stalling engine
  • Odd readings on the car’s dashboard
  • Battery light is on

When a car battery has low voltage due to a malfunctioning alternator, it can throw some random low voltage codes or loss of communication codes (U0100, U0140). 

You can check them using OBD2 scan tool. Due to these trouble codes, the engine can go into a reduced power mode.

Furthermore, when the engine is running at high RPMs, the voltage of the battery should never drop below 13.5V. If it does, it means the alternator is bad.

Must Read: Car keeps killing alternator

7. Faulty AC Pressure Switches

A faulty AC pressure switch can cause your car to lose power and acceleration when the AC is on. The two primary culprits in this situation are low and high-pressure switches.

Both of these switches regulate the flow of refrigerant within the AC system and must be working properly in order for the system to remain functional. 

The low-pressure switch is the more commonly problematic of the two. This switch is responsible for monitoring the pressure of the low side of the AC system and is typically located near the compressor.

When the pressure in the system drops too low due to low refrigerant charge, this switch will shut off the compressor to protect it from damage. If this switch gets stuck in the “on” position, it will continue the compressor clutch to engage and run the compressor.

As a result, the AC compressor will run dry due to low refrigerant charge and will have to work harder to pump the refrigerant.

On the other hand, the high-pressure switch is responsible for monitoring the pressure of the high side of the AC system. This switch is typically located near the condenser and works to protect the AC system from damage caused by over-pressurization.

If this switch gets stuck in the “on” position, the compressor will work harder to push the refrigerant through the AC system and put extra strain on the engine.

So, while AC is running, make sure that the low-pressure side of the AC system has pressure from 30 to 50 psi and the high-side pressure should be around 250 psi.

How Much Horsepower Do You Need For A Car AC?

The car’s air conditioning system requires a certain amount of power to keep it running efficiently. There are several factors that determine the power needed for a car air conditioner, including the size of the vehicle, the type of climate in which you live, and the size of the AC compressor.

In general, the amount of horsepower needed for a car AC will range from 3 to 10 HP or 5% of the total engine’s horsepower. This is enough to keep the car’s air conditioning running at its optimal efficiency.

However, it is important to note that if the car is larger or if the climate is particularly hot, more horsepower may be needed to keep the air conditioning running effectively. 

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