How to Tell if the Home AC Compressor is Bad

Figure 1: HIGHLY air conditioning compressor.

The compressor of the air conditioner can be said to be the core part of the air conditioner. Once there is a problem, the air conditioner will not work normally. Therefore, we can understand the symptoms of a broken air conditioner compressor in advance, and solve the problem or ask for help in time to save costs.

1. Different Types of Air Conditioning Compressors

According to the principle of increasing gas pressure:
1. Positive displacement type (piston type, screw type, scroll type, rolling rotor type)
2. Dynamic type (centrifugal type usually used in commercial refrigeration area)

Classified by the type of refrigerant used:
1. Organic refrigerant type (R22, R404a, R134a)
2. Inorganic refrigerant type (R717, R744)

Classified by sealing method:
1. Open refrigeration compressor
2. Semi-hermetic refrigeration compressor
3. Fully enclosed refrigeration compressor (Hermetic refrigeration compressor)

Figure 2: Flow diagram of air conditioning refrigeration system.

2. Signs of a Damaged Air Conditioner Compressor

The main manifestation of compressor damage is that the air conditioner does not cool and cannot run, and it will also cause damage to the circuit and short circuit of the motor coil. In addition, the noise and vibration of the compressor will become louder, and the performance will decrease.

If the compressor is damaged, you have to turn on the outdoor unit to make an accurate judgment. It is difficult to find the problem just by observing the appearance.

What are the signs of a damaged air conditioner compressor?
External devices are making strange noises
System overheating
Lukewarm air from vents
Water leakage of HVAC system components
Dirty condenser coil
High electricity bill

2.1 Common Causes of Air Conditioner Compressor Damage

Fault phenomenon: The compressor does not run after power-on, but the protector operates.
It is usually a shaft or cylinder sticking or jamming failure caused by the oil loss of the compressor or the entry of impurities.

Fault phenomenon: The refrigeration system does not work or the cooling effect is poor.
Usually it is because the air conditioner compressor suction and exhaust valves are not closed tightly or damaged.

Fault phenomenon: the pipe collides with the casing, the fixing bolts of the compressor are loose, and the shock absorber falls off, etc.
This kind of problem often occurs in maintenance work, and generally does not have much impact on refrigeration performance.

Figure 3: An electrician is overhauling the air conditioning compressor unit.

Fault phenomenon: open circuit or action temperature point becomes smaller.
It is usually a fault of damage to the thermal protector of the air conditioner compressor. This problem is often easily confused with a slight short circuit between the windings. The difference is that the working current is normal when the thermal protector is damaged, and the current is too large when the winding is short-circuited.

Fault phenomenon: when the circuit is broken, the power supply is normal, and the compressor does not work; when the line is short-circuited and touches the shell, the protector will operate or the fuse will be burned after the power is turned on.
Usually the problems are short-circuited, open-circuited air conditioner compressors, and the ground fault of the winding touching the casing, so it is not easy to judge, and it should be judged according to the measured current.

Through the understanding of the failure phenomenon of the air conditioner compressor, you can directly judge the failure of the air conditioner compressor. If the compressor is broken and cannot be repaired, it is recommended to buy a compressor of the original brand and model for replacement.

3. How to Judge Whether the Air Conditioner Compressor is Bad

2.2 Method One

To judge whether the air conditioner compressor is good or bad, you must first learn to identify the three terminals on the air conditioner compressor, which are S, R, and C. S is the starting winding, R is the running winding, and C is the common terminal.

Figure 4: Single-phase compressor wiring diagram.

Then use a multimeter to measure its resistance value. When the resistance values between SC and RC are equal to the value between RS, it is normal data. For example, the resistance values of RC and SC are 5 ohms and 3.5 ohms respectively, then the resistance value between RS is 8.5 ohms (a little deviation is allowed, but not too large).

If the resistance deviation is too large, or there are no resistance values measured between the three, then the compressor is probably bad. But sometimes, even if the value displayed by the multimeter is normal, there is actually a short circuit inside the compressor, which cannot be measured.

In this case, the easiest way is to measure whether the line is connected to the power supply with a multimeter. If it shows that it is powered on, but the compressor does not start, you can try to replace a starting capacitor (50UF). If the compressor does not start after replacing the capacitor, it is undoubtedly that the compressor is broken.

2.3 Method Two

You can judge from the noise level. The noise when the air conditioner is running is mainly produced by the internal evaporator and the external condenser. It is generally stipulated that the noise of the indoor unit of the air conditioner with a cooling capacity below 2000W should not be greater than 45 decibels, and that of the outdoor unit should not be greater than 55 decibels.

The noise of an indoor unit of split air conditioner with cooling capacity between 2500W and 4500W should not be greater than 48 dB, and that of an outdoor unit should not be greater than 58 dB.

Under normal circumstances, the sound is a little loud when the compressor starts. If it is not normal, the sound will be different.

4. How to Maintain the Air Conditioner

1. Remove debris from the vents to ensure proper ventilation. Observe whether the outdoor rack is loose, clean the foreign matter in the outdoor vent mesh, and keep the vents unobstructed.

2. Clean the surface of indoor and outdoor heat exchangers to improve their efficiency.

When cleaning the indoor heat exchanger, carefully remove the panel, and scrub it with a soft rag. Use a small brush to gently scrub the heat exchanger of the indoor unit, so as to remove dust and harmful accumulations that can breed germs.
Note: Since the heat sink is made of very thin aluminum material, it is easy to deform after being stressed, so brush it carefully.

Figure 5: Air conditioner filter cleaning.

3. Clean the dust accumulated on the filter. First cut off the power supply, then open the air intake grille, and take out the filter screen. Clean the filter screen with water or a vacuum cleaner, and the water temperature should not exceed 40 degrees. Wash it with a hot wet cloth or neutral detergent, and then wipe with a dry cloth clean. Do not use insecticides or other chemical detergents to clean the filter screen.

4. Clean out the dirt accumulation from the drain part. The drainage part is easy to deposit dirt, so it must be thoroughly disinfected regularly to ensure smooth drainage and prevent bacteria from multiplying.

5. Check others, including power supply lines, power strips, and switches. Check the condition of consumable parts, such as air guide plate, sterilization and dehumidification, photocatalyst, etc., to ensure that the air conditioner is in good condition and there is no abnormality.

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