How to Measure Whether a Compressor is Good or Bad?

[McKinsley]

To determine the quality of a compressor, it's essential to identify the three terminals on the air conditioning compressor, which are S, R, and C. Here, S stands for the start winding, R for the run winding, and C for the common terminal. Use a multimeter to measure the resistance values. The sum of the resistances between SC and RC should equal the resistance between RS, which indicates normal operation. Below is additional information: 1. Function of the Compressor: The compressor's role is to regulate the start-stop state of the air compressor. By adjusting the pressure inside the air storage tank, it allows the air compressor to shut down for rest, which benefits engine maintenance. 2. Types of Compressors: Compressor types include swash plate compressors, vane compressors, scroll compressors, and reciprocating (crankshaft-connecting rod) compressors.

[DanielRose]

Here are a few practical methods I use to check the condition of an air conditioning compressor. After starting the car and turning on the AC, feel the temperature at the air vents. If it remains warm or doesn't cool down after a few minutes, the compressor might be faulty. Also, pop the hood and listen to the sound when the compressor starts—normal operation should produce a slight humming noise. If you hear knocking or sharp noises, internal components may be worn. Next, connect a pressure gauge to the high and low-pressure lines of the AC system. Normal pressure ranges are 150-250 psi for the high side and 30-40 psi for the low side. If the pressure is too low or fluctuates significantly, it could indicate a compressor or system leak. Additionally, check if the compressor belt is loose or cracked, as excessive looseness can reduce drive efficiency. Measuring current consumption is another simple method—use a multimeter to check the input current at the compressor relay. If it exceeds 10-15 amps, the motor may be overheating or seized. Compressor failures are often accompanied by oil or refrigerant leaks, so inspect the area around the compressor for oil stains. Ignoring these issues can lead to complete system failure, so I recommend checking the compressor oil level and pressure during regular maintenance to avoid costly repairs.

[DeEmiliano]

As someone who frequently tinkers with cars in the garage, I first assess the compressor's condition through sensory checks: After turning on the AC, does the cabin temperature drop quickly? If it remains hot after a long wait, the compressor is likely faulty. I also carefully listen to the sounds from the engine bay—a properly functioning compressor should run smoothly with a steady rhythm, without any squeaking or metal grinding noises, which could indicate a bad bearing. Another reliable method is connecting a pressure test tool; even a simple high-pressure gauge can reveal abnormal readings. When the refrigeration system pressure is unstable or too low, the compressor may be running but ineffective. For electrical checks, I often use a multimeter to measure the resistance of the compressor's electromagnetic clutch coil. Normal resistance should be between 10-20 ohms. If it shows infinity or is too low, the coil is likely burnt out, preventing engagement. Belt issues are also easily overlooked—manually pressing the belt to check for obvious slack or cracks is essential, as poor transmission can hinder compressor efficiency. If these signs are detected, address them early to avoid prolonged refrigerant leaks, which harm the environment. Regularly inspect the AC every six months to prevent breakdowns during hot weather.

[LaAmelia]

When testing the compressor's condition, I started with the basics. Turn on the AC and observe the cooling effect—the air should feel icy cold. If it's warm or unchanged, the compressor might be failing. Then, start the car and listen carefully: normal operation produces a low humming sound, while unusual noises like clanking are warning signs. A simple pressure gauge can help: the high-pressure pipe should maintain stable pressure; readings below the normal range (e.g., 150 psi) indicate a leak or compressor damage. Also, inspect the compressor for oil stains or corrosion, as leaks often occur due to seal aging. Checking the electromagnetic clutch is crucial—use a multimeter to ensure resistance falls within the standard range. These tips help detect issues early and prevent major problems.