How To Reduce AC Load On Engine? [9 Steps]

Are you tired of the constant strain on your engine caused by your air conditioning system?  Many car owners find themselves faced with the challenge of reducing the AC load on their engine to improve its performance and longevity. In this article, we will explore some effective techniques to help you decrease the strain on your engine and enhance your overall driving experience.

So, how to reduce AC load on the engine? To ease the AC load on your engine, follow these helpful techniques: First, utilize the recirculation function on your car’s AC to cool already chilled interior air, reducing strain on the engine. Park your vehicle in shaded areas whenever feasible, preventing excessive heat buildup and aiding the AC in cooling the cabin effectively. Enable the ECO idle system, if available in your car. Rather than immediately blasting at full power, gradually adjust the temperature setting on your climate control AC. Regularly check and clear any debris from the AC compressor and condenser. Lastly, maintain a smooth driving style, avoiding sudden accelerations or decelerations that burden the engine and AC system.

Bonus Read: Car loses power when AC is on

How Does AC Work In Engine?

At its core, the AC system works by removing heat and humidity from the air inside the vehicle. This is achieved through a series of components, including the compressor, condenser, expansion valve, and evaporator. The compressor, driven by a belt connected to the engine, is responsible for pressurizing and circulating the refrigerant throughout the AC system.

The cycle starts when the refrigerant gas enters the compressor as a low-pressure vapor. The compressor squeezes the gas and increases its pressure and temperature. The hot, high-pressure gas then leaves the compressor and flows to the condenser.

The condenser is a radiator-like device that is mounted in front of the engine radiator. It cools down the refrigerant gas by releasing heat to the ambient air. As the gas cools down, it changes from a vapor to a liquid. The liquid refrigerant then passes through a receiver-drier, which removes any moisture or impurities from it.

The liquid refrigerant then reaches an expansion valve, which regulates its flow into the evaporator. The evaporator is another radiator-like device that is located inside the car’s dashboard. It absorbs heat from the cabin air and causes the liquid refrigerant to boil and evaporate. The cold, low-pressure vapor then returns to the compressor to complete the cycle.

How Does AC Exert Load On the Engine?

The AC system exerts load on the engine because it requires mechanical power to operate. The AC compressor is the main component that exerts a load on the engine while it is running as it is mechanically driven by the engine’s crankshaft.

Other components i.e. condenser and blower/fan (blows air over the evaporator) run from the vehicle’s battery. So, they exert only a small percentage of the load. However, the blower speed can indirectly affect the load on the engine which I have discussed in the next section of this guide.

In a car air conditioning system, an AC compressor has a pulley connected to the engine’s crankshaft via a serpentine belt. 

The AC compressor has an electromagnetic clutch that is engaged or disengaged with the compressor pulley. When the electromagnetic AC clutch is engaged with the compressor pulley, the compressor is run to your vehicle’s cabin.

As soon as the compressor clutch is engaged with the pulley and the compressor runs, it exerts a load on the engine. This is because a part of the power produced by the engine is used to overcome the resistance offered by the AC compressor.

If only the AC compressor pulley is spinning and the clutch is not engaged, it will not exert load or strain on the engine.

So, in short, the AC compressor pulley spins all the time via a serpentine belt as long as the engine is running. Only the compressor clutch engages or disengages depending on the AC settings or condition of your vehicle’s air conditioning system.

How Is Load On Engine Interpreted?

Engine load can be thought of as the demand placed on the engine to produce power. It is commonly measured in terms of torque or horsepower, which represent the engine’s ability to deliver force or work. The load on an engine can vary depending on several factors, including the vehicle’s weight, speed, road conditions, and the driver’s behavior. 

Basically, the more resistance engine’s crankshaft face during rotation, the more load is exerted on it. As a result, the engine has to turn at a bit higher speed to produce more power so that it can overcome the resistance offered by the AC compressor.

I would suggest you perform an experiment. First, start your engine without AC. Keep looking at the RPM meter. Now, press the AC button. As soon as you press the AC button, you will see that the RPM needle will move up a bit, which means that there is more load on the engine and it is producing more power. If your engine has a digital RPM meter, you can easily spot the difference.

The load can also affect your engine’s performance by changing its operating temperature. When you use your AC, you increase the heat generated by both your engine and your AC system. This heat has to be dissipated by your cooling system, which consists of your radiator, your water pump, your thermostat, and your cooling fan.

If your cooling system is not working properly or is overwhelmed by too much heat, your engine can overheat and cause serious damage. Moreover, your vehicle’s AC will not blow cold air. That’s why you should always check your coolant level and condition regularly, especially in hot weather or when using your AC frequently.

How To Reduce AC Load On Engine?

You can reduce AC load on the engine in the following ways:

1. Turn Air Recirculation On

air circulation button of car ac

One simple and effective way to reduce the AC load on your engine is to turn on the air recirculation feature. When you turn on this setting, your vehicle will circulate the already-cooled air inside the cabin, rather than constantly cooling down the hot air from outside.

By doing so, you reduce the need for the AC system to work harder, resulting in less strain on the engine.

If you turn off recirculation and set the fresh-air mode, the hot air will flow over the evaporator coils. The higher the air temperature, the more load will be exerted on the AC compressor to reduce the air temperature.

Let’s think about it that way. Where quite hot air is blown over cold evaporator coils due to the refrigerant flowing inside them, it exchanges heat with them.

That huge temperature difference between evaporator coils and hot ambient air is interpreted as a ‘load exerting on the compressor’ to demand more cooling.

However, if recirculation mode is on and already cool air flows over a cold evaporator, there is a lesser temperature difference between cold evaporator coils and the vehicle’s cabin air. Due to this reason, there will be less load on the AC compressor and it will kick off quite open as it does not have to keep on compressing the refrigerant and flowing it through the AC system for cooling.

Vehicles with climate control instead of manual AC have the advantage that they automatically turn air recirculation on and off to maintain the humidity of the cabin’s air and to minimize load on the engine.

2. Park in Shaded Areas

Another practical technique to reduce the AC load on your engine is by parking in shaded areas whenever possible.

When your vehicle is exposed to direct sunlight in extremely hot weather, the interior can heat up significantly, requiring the AC system to work harder to cool it down.

By parking in shaded areas or using sunshades on your windows, you can prevent excessive heat buildup, reducing the need for the AC to run at maximum capacity.

If, however, you couldn’t manage to park your vehicle in a shaded area, whenever you start your engine, don’t turn on the AC right away. Instead, roll the windows down and turn off air recirculation for a few minutes to allow fresh air to enter and lower the vehicle’s cabin temperature. Then, you can start the AC.

3. Enable the ECO idle Mode

eco idle in vehicles

Some vehicles come equipped with an eco idle mode feature, which automatically shuts off the engine when the vehicle is at a standstill, such as when waiting at a traffic light or in a drive-thru.

Here, I am not talking about hybrid vehicles as their AC is run by the battery instead of the engine. So, even with the ECO idle mode on, the AC of hybrid vehicles is not turned off at idle.

In conventional vehicles, in which AC is driven by the engine, the AC compressor also kicks off at idle if the ECO idle mode is on.

When you release the brake pedal or press the accelerator, the engine quickly restarts to resume normal operation. In this way, you can reduce the AC load on the engine if you’re stuck in traffic or have to frequently travel through the areas where you have to frequently apply the brakes.

4. Use Window Shades

car window shades

Another effective way to reduce the AC load on your engine is by using reflective window shades. These shades are designed to block out the sun’s heat and radiation, preventing them from entering your vehicle.

By placing these shades over your windows, especially on the rear window, you can significantly reduce the amount of heat that infiltrates your car’s interior. As a result, your AC system won’t need to work as hard to cool down the cabin, leading to reduced strain on the engine.

5. Gradually Adjust Temperature Setting On Climate Control AC

climate control temperature setting

Imagine this scenario: you step into your sweltering car, and instinctively crank up the AC to the coldest setting possible.

While this may provide immediate relief, it also puts a tremendous strain on the engine. The sudden demand for cooling places an instant load, causing the engine to work harder and consume more fuel. 

Now, let’s consider a different approach. Instead of going from hot to cold in an instant, try adjusting the temperature gradually. Start by setting the AC at a moderate, comfortable temperature and allow the cabin to gradually cool down.

Once you reach the desired level of coolness, you can then fine-tune the temperature as needed. This method eases the load on the engine and reduces the sudden spike in energy consumption. 

Now, I will explain why I am telling you to do so. Engines with climate control AC instead of manual work a bit differently.

Just like your home AC system, a certain temperature is set for your climate control AC.

Climate control works with the following sensors:

  • Interior Temperature Sensor
  • Sunlight Sensor
  • Humidity Sensor
  • Occupancy Sensor
  • Engine Coolant Temperature Sensor
  • Ambient Air Temperature Sensor

Above are the basic sensors climate control works with. They can vary with your vehicle. The more sensors climate control AC, the more efficiently it will work and reduce the load on the engine.

So, when you start the engine and set the higher temperature setting initially, the compressor will kick off more often and reduce the load on the engine.

6. Set Low Fan Speed

vehicle manual ac fan knob

This point is only for those vehicles equipped with manual AC. Although fan speed does not directly exert load on the engine as it is run by the battery. But, indirectly, it does. 

Before I explain further, I will give you a clue so that you can believe what I’m saying.

Start the engine, press the AC button while keeping the fan off. Now, pop up the hood and observe the compressor. You will see that it will not be turning. 

When my engine is idling, its compressor has a humming sound when it’s running. So, in my vehicle, I tested it without popping up the hood and noticing the compressor.

I turned on the AC and kept the fan off. I didn’t hear any sound from the compressor. But, as soon as I turned on the fan even to the ‘1’ setting, I could hear the compressor sound.

Now, I will explain why fan speed is important in a vehicle with manual AC.

The AC compressor engages and disengages based on responses from high and low-pressure switches and evaporator temperature sensor.

Basically, when the fan speed is low, air will flow with less speed over the coils of the evaporator. As a result, there will be less heat transfer from the air flowing over the evaporator to the refrigerant in the coils of the evaporator.

Due to less heat transfer between air and refrigerant, the refrigerant will still be cooler. If AC compressor keeps on running, the coils of the evaporator will freeze up. To prevent this, the AC compressor kicks on and off more often at a lower fan speed.

As you increase the fan speed setting to ‘3’ or ‘4’, air will flow over the evaporator at a higher speed. This will increase the heat transfer from cold refrigerant to hot air. As a result, the compressor has to keep on running to keep the refrigerant flowing in order to meet the demands of that heat transfer. This will increase the load on the engine.

7. Keep Serpentine Belt in Good Condition

The serpentine belt plays a vital role in powering various components of your vehicle, including the AC compressor. A worn-out or damaged belt can cause the compressor to work harder than necessary, resulting in increased engine load. Therefore, it is crucial to regularly inspect the condition of the serpentine belt.

To do this, open the hood of your vehicle and locate the belt. Look for signs of wear such as cracks, fraying, or glazing. If you notice any of these issues, it is time to replace the belt. Additionally, ensure that the belt is properly tensioned. A loose belt can result in slippage and decreased AC efficiency, while an overly tight belt can strain the engine. 

8. Ensure the Condenser Is Not Plugged Up

The condenser is an integral part of the vehicle’s air conditioning system. Its primary function is to remove heat from the refrigerant, which is circulated through the AC system. The condenser is located just after the AC compressor.

The process involves converting the high-pressure gas refrigerant into a high-pressure liquid by dissipating heat to the surrounding air. This allows the refrigerant to cool down and prepare for the next phase of the cooling cycle. 

When a condenser becomes plugged, it restricts the flow of refrigerant through its tiny passages. As a result, the AC compressor has to work harder to push refrigerant through the AC system at a constant flow rate. This will exert additional load and strain on the engine.

9. Compressor Is Not Locked Up

A locked up compressor creates resistance within the air conditioning system, which makes it harder for the engine to power the compressor. This increased resistance places a greater load on the engine, requiring it to work harder to overcome the obstruction. As a result, the engine needs to generate more power and use more fuel to maintain the same level of performance. 

The additional workload imposed on the engine due to a locked-up compressor can have several negative effects. First and foremost, it can lead to decreased fuel efficiency. The engine has to work harder to maintain the desired temperature inside the cabin, which causes it to consume more fuel than usual. 

Furthermore, the strain on the engine can also result in reduced power output. Since the engine is occupied with powering the locked-up compressor, it may not be able to deliver its full potential. This can lead to sluggish acceleration and overall diminished performance. 

In addition, the increased resistance from the locked-up compressor puts added stress on the drive belt, which connects the engine to the compressor. Over time, this can lead to belt wear and eventually cause it to break. You can learn more in my guide on car losing power due to locked ac compressor.

Other Factors Affecting The Load On the Engine

Apart from the AC compressor, worn-out or incorrectly inflated tires can significantly impact the load on the engine. When the tread on your tires wears down or they are underinflated, they create more rolling resistance, increasing the load on the engine.

Furthermore, installing a bigger tire than the recommended size can also exert strain on the engine.

The oil viscosity also matters a lot to minimize load on the engine. The oil pump is also driven mechanically by the crankshaft.

If you use a thicker oil than the recommended one, the oil pump will need to work harder to push the thicker oil through the engine’s passages. This increased workload can lead to additional strain on the engine and potentially reduce its overall performance. To learn more, you can read my guide on SAE 30 vs 10W30.

Lastly, driving habits can significantly impact the load on the engine. Aggressive driving, such as rapid acceleration and hard braking, can cause unnecessary strain on the engine. By adopting a smoother driving style, you can reduce the load on the engine and improve fuel efficiency.

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