How to Add Oil to AC Compressor

Figure 1: AC compressors.

When the all-in-one air conditioner leaves the factory, there is a sufficient amount of AC compressor oil (commonly known as refrigeration oil, refrigerant oil, AC lubricants, AC oil) inside the machine. So generally, there is no need to add or replace the refrigerant oil in the air conditioner compressor (air conditioner compressor).

Before explaining how to add refrigeration oil to the AC compressor, we should understand why it is necessary to add refrigeration oil to the compressor.

1. Functions of Compressor Refrigeration Oil

The AC compressor oil is a special lubricating oil that can work normally under high and low temperature conditions. Its general functions are:

1) Lubrication: It can lubricate the surface of moving parts of the compressor, reduce resistance and friction, reduce power consumption and prolong service life.

2) Cooling: It can take away the heat generated by the friction of the moving surface in time to prevent the compressor from being overheated or burned out.

3) Sealing: It penetrates into the sealing surface of each friction part to form an oil seal, which plays a role in preventing refrigerant leakage.

4) Reducing the noise of the compressor: It continuously washes the friction surface and takes away the wear debris, which can reduce the noise generated by the wear of friction parts.

Refrigeration oil is completely dissolved in the refrigerant in the air-conditioning refrigeration system, and circulates together with the refrigerant.

Figure 2: Refrigeration oil.

2. How Do You Add Oil to Your AC Compressor?

The air conditioner compressor plays the role of compressing and driving refrigerant in the air conditioner refrigeration circuit. Home air conditioner compressors are generally installed in outdoor units.

Figure 3: Diagram of adding refrigeration oil by pulling a vacuum.

1—Low pressure manual valve closed 2—High pressure manual valve opened 3—Discharging air 4—Vacuum pump 5—Refrigeration oil

Steps for changing refrigeration oil in home AC compressors:
1. Drain all the refrigerant in the system.
2. Use a vacuum pump to evacuate to make the inside of the air conditioner a negative pressure.
3. Unscrew the pipe of the vacuum pump and quickly insert it into the refrigerant oil box. Since the compressor is under negative pressure, the oil is sucked in.
4. Fill the refrigerant according to the normal procedure.

What is the oil capacity of original AC compressors? This is mainly related to the internal structure of the AC compressor itself and the applicable air conditioner. In general:

Table 1: AC compressor oil capacity chart.

3. How Do I Add Oil to a Car AC Compressor?

Under the premise of normal use of car air conditioners (there is no problem with compressor refrigeration), there is no need to add refrigeration oil. In the refrigeration system, the consumption of refrigeration oil is very small, and air conditioning compressors that operate normally do not require adding refrigerant oil.

Whether to add refrigerant oil to the car AC compressor depends on the situation:
1). It is necessary to add new refrigeration oil into the system when the old car AC compressor needs replacing.

2). If the condenser or evaporator needs replacing, refrigeration oil must be added, so as not to cause damage to the compressor due to insufficient refrigeration oil.

3). If there is leakage of refrigerant, including sealing ring leaking and air conditioning pipeline leaking, in this case, after the leak is repaired, it is necessary to add refrigeration oil before charging the refrigerant.

The filling amount and the type of the refrigeration oil are detailed in the product technical manual from the compressor manufacturer. So, how is the car AC compressor oil added?

There are three main ways to add refrigerant oil to car AC compressors: first is direct filling, second is filling from the high pressure side, and the third is filling from the low pressure side, which can be applied according to the actual situation.

3.1 Directly Adding

Before adding, first operate to return all the oil remaining in the control system to the compressor, then turn off the engine, release the refrigerant, remove the compressor, pour out the old oil, and then just pour in new oil directly through the cock of the compressor.

Figure 4: The refrigeration oil lid of the compressor.

3.2 Fill from the High Pressure Side

Pull a vacuum on the system to 98kPa, close the manual valve on the high-pressure side, close the service valve on the compressor, remove the high-pressure side hose from the head of the pressure gauge, and insert it into the refrigeration oil.

Open the service valve, and the refrigerant oil will be sucked in. Immediately close the service valve at the end of the oil suction to avoid sucking in air.

Then connect the high-pressure hose to the gauge head again, open the manual valve on the high-pressure side, continue pulling a vacuum, and then add refrigerant. The engine and vacuum pump should not work when adding oil.

Figure 5: Pressure gauge.

3.3 Fill from the Low Pressure Side

Filling in from the low-pressure side does not need a service valve. After pulling a vacuum on the system to 98kPa, close the manual valve on the low-pressure side, and the vacuum pump continues to work.

Keep the high-pressure side manual valve open, remove the low-pressure side hose from the head of the pressure gauge, insert it into the refrigeration oil to suck oil.

Reconnect the hose to the gauge head after sucking, open the low-pressure side manual valve, and continue pulling a vacuum. Refrigerants can be added after pulling a vacuum.

Note that too much refrigerant oil will result in poor refrigeration, and if the refrigerant oil is too little, the compressor is easily damaged, so it must be filled according to the specified amount.

3.4 Precautions for Filling Refrigerant Oil into Car AC Compressor

Figure 6: Diagram of adding refrigeration oil to the system.

1. Under normal circumstances, the refrigeration system of car air conditioners consumes very little refrigeration oil, which can be replaced every two years.

2. If the amount of refrigeration oil in the system is low, the compressor will overheat and even cause cylinder scuffing. If there is too much refrigerant oil in the system, the expansion valve and evaporator will fail, so it is necessary to maintain a certain amount of oil in the AC compressor.

3. Through the liquid sight glass installed on the compressor, the amount of refrigeration oil in the compressor can be observed. If the refrigerant oil level of the compressor exceeds 80% of the height-to-width ratio of the sight glass, it is generally considered appropriate. If the liquid level is above this limit, drain excess refrigeration oil, and if the liquid level is below this limit, add more refrigeration oil.

4. Refrigeration oil filling amount (How much oil do I put in my AC compressor?): There is no need to add the refrigeration oil when there is a small leakage in the refrigeration system, but it is necessary to add the refrigeration oil when the leakage is large (about 15mL).

·If the condenser is replaced, add 30-50mL of refrigerant oil.
·If the evaporator is replaced, add 30-50mL of refrigerant oil.
·If the drier is replaced, add 10-30mL of refrigerant oil.
·If the compressor is replaced, add 40-60mL of refrigerant oil.
·If the pipeline is replaced, add 10-20mL of refrigerant oil.

5. Refrigeration oil is easy to absorb water, and the oil storage bottle should be tightly closed after use.

6. Avoid using spoiled refrigeration oil. The inspection method is to put a drop of oil on a piece of white paper, and wait for a while. If there is a black spot in the middle of the oil drop, it means that the refrigeration oil has deteriorated and cannot be used.

7. Refrigerant oils of different brands cannot be mixed.

4. How Do I Know if My AC Compressor Needs Oil?

When your car AC compressor has the following conditions, it means that it is time to add refrigeration oil:

When the amount of refrigerant oil in the pipeline of the car air conditioning system is insufficient, the power from the car consumed by the air conditioner becomes more, and the effect of the air conditioner becomes worse, and the gas discharge temperature of the air conditioner compressor increases.

If the system has been repaired many times but the refrigeration oil has not been replenished or there is a large amount of oil stains along the pipeline of the air conditioning system, it is possible that the refrigeration oil in the system is insufficient.

When the air conditioner is turned on during the normal driving of the car, you may feel the car is "powerless". This is because the air conditioner compressor runs due to lack of oil, and the friction between its internal mechanical parts becomes larger, and the kinetic energy required to consume becomes larger.

When it is found that the car air-conditioning system is short of oil, stop using the air conditioner, and it is necessary to go to the repair shop for repairs and maintenance.

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