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AC Compressor

By R&D
Published on December 26th, 2023

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The first air conditioning systems were installed in passenger vehicles in the 1930s to improve occupant comfort when travelling during hot weather conditions. And the technology used in air conditioning systems has continuously evolved ever since. The Air Conditioner (AC) compressor is the central component of the air conditioning system. This article describes the purpose and operation of the AC compressor, identifies possible symptoms of a malfunctioning compressor, outlines maintenance considerations, and reviews potential costs associated with repair and replacement.

Overview of the AC Compressor Operation

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AC Compressor Operation

The AC compressor in a vehicle is a principal component of the vehicle's Heating, Ventilation, and Air Conditioning (HVAC) system. Its primary function is to compress and circulate refrigerant to facilitate cooling of the vehicle’s cabin. This is accomplished as follows:

1. Circulation of Refrigerant: The AC system in a vehicle operates using a closed-loop system that circulates a specialized refrigerant fluid. The refrigerant is responsible for transferring heat from inside the vehicle to the outside, resulting in cooler cabin temperatures.

2. Compressor Engagement: When the vehicle's AC system is first turned on, or when the temperature setting is adjusted /during operation to a lower setting, it sends a signal to the AC compressor clutch. The compressor clutch engages the compressor's operation. In electric vehicles, the AC compressor is driven by the electricity of the vehicle instead of being driven by a belt connected to the vehicle’s engine.

3. Compression: In most cases, the AC compressor is driven by a serpentine belt connected to the vehicle's engine. When the compressor is engaged, a piston or rotary mechanism within the unit starts to compress the low-pressure, low-temperature refrigerant vapor. The compressor is typically engaged by a magnetic clutch mechanism.

4. Pressure Increase: As the compressor operates, it increases the pressure and temperature of the refrigerant gas significantly. This process converts the refrigerant from a low-pressure vapor into a high-pressure, high-temperature gas.

5. Heat Exchange: The hot, high-pressure refrigerant gas is then sent to the vehicle's condenser coil, usually located in front of the vehicle's radiator. Airflow from the vehicle's forward motion (or from a dedicated electric fan) helps dissipate the heat from the refrigerant to the surrounding air. This causes the refrigerant to condense and change from a gas into a high-pressure liquid.

6. Expansion Valve: The high-pressure liquid refrigerant then flows through an expansion valve or orifice. Here, the refrigerant experiences a sudden drop in pressure, resulting in a significant temperature decrease. This causes the refrigerant to become a low-pressure, low-temperature liquid-gas mixture.

7. Evaporation: The cold refrigerant is then routed to the vehicle's evaporator coil, typically located inside the dashboard or near the HVAC unit. A blower fan forces warm cabin air over the evaporator coils. As the refrigerant absorbs heat from the cabin air, it evaporates back into a low-pressure vapor.

8. Cooling Effect: The heat absorbed from the cabin air during this evaporation process creates a cooling effect, reducing the temperature and humidity of the air inside the vehicle.

9. Continuous Cycle: The cycle repeats itself as the low-pressure vapor is drawn back into the compressor, where it is compressed again to repeat the process. This continuous cycle of compression, heat exchange, and expansion is what enables the vehicle's AC system to maintain a cool and comfortable interior cabin temperature, even in hot weather conditions.

Common Symptoms of a Faulty AC Compressor

A malfunctioning AC compressor can cause several common symptoms that may indicate an issue is present. Some of the most common symptoms of a faulty AC compressor include:

1. Lack of Cold Air: One of the most obvious signs of a compressor problem is when the air coming from the AC vents warm (or is not as cold as it should be). This may indicate the compressor is not compressing the refrigerant properly.

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Lack of Cold Air

2. Loud or Unusual Noises: A failing or damaged compressor can produce unusual noises. Loud clunking, grinding, or squealing sounds may be present when the AC is running. These noises can indicate damage to the compressor's internal components.

3. AC Clutch Not Engaging: The AC compressor has a clutch that engages and disengages to control the flow of refrigerant. If the clutch doesn't engage when the air conditioning system is turned on, it can indicate a problem with the clutch itself or an issue with the compressor.

4. Leaking Refrigerant: A leaking AC system is a common issue and can be caused by a damaged compressor. If you notice refrigerant leaks (puddles of fluid under your vehicle) or a hissing sound coming from the AC system, it is essential to address it promptly.

5. Decreased Fuel Efficiency: In the case of belt-driven compressors, malfunctioning AC compressor can put extra stress on the engine, leading to reduced fuel efficiency and potential engine camage. with a significant increase in fuel consumption accompanied by AC issues may be related to a faulty compressor.

6. Visible Damage: In some cases, a damaged AC compressor will show visible signs of physical damage, such as oil leaks, loose or damaged belts, or a visibly damaged clutch. These are clear indicators that the compressor needs attention.

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Visible Damage

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AC Compressor Maintenance

Proper maintenance of the AC compressor is essential to ensure that the air conditioning system works efficiently and remains in good condition. Use the following maintenance practices to keep the AC compressor in good condition:

1. Regular Inspections: Include AC system checks as part of the routine vehicle maintenance schedule. This can help identify early signs of issues before they become major problems.

2. Check for Leaks: Inspect the AC system for refrigerant leaks. Look for oily residue around connections, hoses, and the compressor itself. If a refrigerant leak is suspected, repair it promptly, as refrigerant is harmful to the environment and can be dangerous if inhaled.

3. Monitor AC Performance: Pay attention to the cooling performance of the AC system. If a decrease in cooling effectiveness, unusual noises, or changes in airflow are present, it could be a sign of compressor issues or other AC system problems.

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Monitor AC Performance

4. Check Belt Tension: Ensure that the AC compressor belt is properly tensioned. A loose or damaged belt can affect the compressor's operation. If the belt is cracked or shows signs of wear, replace it.

5. Recharge Refrigerant: If the AC system is not cooling properly, it may need a refrigerant recharge. However, this should be done by a qualified technician to ensure the correct refrigerant type and proper charge levels.

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Recharge Refrigerant

6. Professional Maintenance: Periodically, it's a good idea to have the AC system professionally serviced. A qualified technician can perform a thorough inspection, check refrigerant levels, clean components, and address any issues that may be developing.

Cost of AC Compressor Replacement

It is essential to address AC compressor issues promptly to avoid further damage to the air conditioning system, the engine and related components. The cost of repairing or replacing an AC compressor can range from $200 to $500. However, costs may vary depending on the vehicle make and model, the extent of the damage, and labor charges. On average, AC compressor-related repairs .


With having to use the car regularly in hot weather, the car's cooling system is an indispensable part. The AC compressor is the heart of this system. Understanding common symptoms of a malfunctioning AC compressor will aid in early diagnosis and timely repairs, preventing engine performance issues and potential damage. Regular maintenance (including adherence to recommended service intervals) and the use of high-quality refrigerant will contribute to the smooth operation of the AC system, ensuring AC compressor efficiency and longevity.

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