What is the function of the car compressor?
The automotive air conditioning compressor is the heart of the air conditioning refrigeration system, functioning to compress and convey the refrigerant vapor. Compressors are classified into two types: fixed-displacement and variable-displacement.
Based on the different working principles, air conditioning compressors can be divided into fixed-displacement compressors and variable-displacement compressors.
Fixed-displacement compressor
The displacement of a fixed-displacement compressor increases proportionally with the increase in engine speed. It cannot automatically adjust the power output according to the cooling demand and has a significant impact on engine fuel consumption. Its control is generally achieved by collecting the temperature signal from the evaporator outlet. When the temperature reaches the set value, the compressor electromagnetic clutch releases, and the compressor stops working. When the temperature rises, the electromagnetic clutch engages, and the compressor starts working. The fixed-displacement compressor is also controlled by the pressure of the air conditioning system. When the pressure in the pipeline is too high, the compressor stops working.
Variable-displacement air conditioning compressor
The variable-displacement compressor can automatically adjust the power output according to the set temperature. The air conditioning control system does not collect the temperature signal from the evaporator outlet but controls the compressor's compression ratio based on the pressure change signal in the air conditioning pipeline to automatically adjust the outlet temperature. During the entire cooling process, the compressor is always working, and the adjustment of the cooling intensity is completely controlled by the pressure regulating valve installed inside the compressor. When the pressure at the high-pressure end of the air conditioning pipeline is too high, the pressure regulating valve shortens the piston stroke in the compressor to reduce the compression ratio, thereby reducing the cooling intensity. When the pressure at the high-pressure end drops to a certain level and the pressure at the low-pressure end rises to a certain level, the pressure regulating valve increases the piston stroke to increase the cooling intensity.
Air conditioning compressor failures can be caused by various reasons such as circuits, refrigerant, and mechanics. A systematic and step-by-step troubleshooting approach is required. Many local faults (such as clutch, coil damage) can be repaired at a low cost without replacing the entire compressor.
Common Fault Causes
Circuit system failure: This is the most common and easiest to troubleshoot reason. The air conditioning fuse blows, the relay is damaged, or the wiring harness plug is loose/corroded, which can cause the compressor to lose power.
Refrigerant and pressure abnormalities: When refrigerant leakage causes the system pressure to be too low, the low-pressure protection switch will cut off the power to the compressor; high pressure will trigger the high-pressure protection. When the refrigerant is insufficient, the return of the refrigerating oil decreases, and it can also lead to insufficient lubrication of the compressor and wear.
Mechanical failure:
Electromagnetic clutch failure: The clutch coil burns out, the suction cup wears out or the gap is improper (the standard value is usually 0.35-0.50mm), which can cause the clutch to fail to engage or slip.
Transmission belt problem: The belt is too loose and slips, or too tight and can cause the compressor to get stuck.
Internal damage of the compressor: Long-term lack of oil, impurities entering, or high-load operation can lead to wear and sticking of internal components such as bearings and pistons, which is the most serious type of failure.
Sensor or control module failure: Faults in the air conditioning pressure sensor, interior temperature sensor, or the air conditioning control module (ECU) can cause the system to misjudge and instruct the compressor to stop.
Fault Symptoms
Significant decrease or complete loss of cooling effect: This is the most obvious manifestation.
The compressor does not work: After pressing the AC button, there is no "click" sound of the clutch engaging in the engine compartment, and the compressor pulley rotates empty.
Abnormal noise: Metal friction, knocking, or "sizzling" sounds occur during operation, which may indicate internal mechanical wear or clutch slipping.
Abnormal system pressure: By testing with a professional pressure gauge, the high and low pressure values may be simultaneously too low (refrigerant shortage), too high, or too low.
Visible leakage or oil stains: Oil stains appear at pipeline interfaces, condensers, etc., indicating refrigerant (containing refrigerating oil) leakage. Troubleshooting and Maintenance Suggestions
Follow the step-by-step troubleshooting process from simple to complex:
Initial Inspection: Confirm that the AC key is turned on and the air volume is sufficient; listen for suction and operation sounds from the compressor; check the air conditioning fuses and relays (for interchangeable testing).
Advanced Diagnosis: Use an air conditioning pressure gauge to detect system pressure; check the tension of the transmission belt; check the clutch clearance and coil resistance.
Professional Repair: If the above steps are ineffective, it may be necessary to use a diagnostic tool to read fault codes, or have a professional technician inspect the internal mechanical condition.
Operations involving refrigerant require professional handling: Leak detection and refrigerant replenishment must be done using professional equipment and added in accordance with vehicle manual standards. Do not mix different types of refrigerants (such as R134a and R1234yf).
When replacing the compressor, it is necessary to simultaneously maintain the system: If it is necessary to replace the compressor, the dryer bottle should also be replaced and the pipes should be cleaned to prevent impurities from damaging the new components.
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