Why Double-Capped PAG for AC Compressor Lubrication?

With the rapid development of China's automobile industry and the improvement of people's living standards, cars are gradually entering thousands of households. In recent years, the number of vehicles has increased sharply, and consumers' demand for comfortable driving and riding has also risen accordingly.

As a key configuration of improving comfort, the automobile air conditioning system has been the standard feature of the mobile industry.

While the automatic air conditioning technology is developing rapidly, global protection regulations are becoming increasingly strict, the refrigerant technology is undergoing a major transformation: gradually shifting the traditional ones to new types of refrigerant like R134a and R1234yf, which puts a higher demand for compressor lubricant oil.

Double-capped PAG has been the ideal choice for the new refrigeration compressor oils because of its unique chemical structure.

 

Refrigeration technology of automotive compressor oil

The automobile air conditioning system consists of a compressor, an electrically controlled clutch, a condenser, a liquid storage dryer, an expansion valve, an evaporator, pipes, a fan, and a controlling system. Refrigerant R-134a is compressed from low-temperature and low-pressure gas into high-temperature and high-pressure gas in the compressor. And then the gas goes through the condensation to become high-pressure and middle-temperature liquid, and through dehumidification, buffering, throttling, and pressure reduction, the liquid turns to gas in the evaporator. Through absorbing a large amount of heat (the air in the carriage) to reduce the temperature, the refrigerant gas is inhaled in the compressor again and continuously finishes the refrigeration cycle.

The refrigerant of automobile air conditioning is mainly HFC-134a (R134a) and HFO-1234yf (R1234yf), whose matched refrigeration oil is polyether type. This is mainly because the automobile car conditioning requires that refrigeration oil and refrigerants have proper compatibility, better lubricity for the sliding parts of the compressors, hydrolysis resistance, and material adaptability.

 

 

What is double-end capped PAG?

Double-capped polyalkylene glycol is a polyether synthetic oil with both ends of the molecular chain capped by the chemical groups (such as alkyl groups, ester groups, etc.) Compared with traditional PAG (single-capped polyalkylene glycol or uncapped PAG), the molecular structure of double-end capped PAG undergoes performance improvement, increasing the thermal stability, hydrolysis resistance, and compatibility with refrigerants significantly.

 

The advantages of double-end capped (PAG) in air conditioning and refrigeration systems

• Excellent lubricity: di-capped PAG has a much lower friction coefficient, which can reduce the wear of internal parts of the air conditioner compressor.
• Good compatibility with refrigerants: double-end capped PAG has a good compatibility with the often used HFC-type refrigerants (like R32, R410A) in air conditioner systems. It is mentioned in "Performance and Application of Lubricant Oil for Air Conditioners" that the mix of them can form a stable solution without stratification, ensuring the normal operation of the air conditioner compressor.
• Excellent high temperature stability: di-capped PAG performs stably under high temperatures."Synthetic Lubricant Oil and Their Application" mentions that it has good thermal stability under the environment of below 150℃, and it's hard to decompose and beneficial to maintain the lubricant oil performance of the air conditioner compressor for long use.
• Good low-temperature fluidity: under low temperature, double-end-capped polyalkylene glycol can maintain better fluidity. The related researches show that, the pour point can be as low as - 40℃, ensuring the smooth start and operation of the air conditioner under the cold environment.

 

Compared with single-end capped PAG, double-end-capped polyalkylene glycol has a higher thermal stability, better hydrolytic stability, wider refrigerant compatibility, superior lubricity, and lower hygroscopicity. Therefore, double-end capped PAG is suitable for air conditioner refrigerants and has perfect compatibility with refrigerants like R1234f.

 

The Performance Comparison Between Double-end Polyether and Single-end Polyether

Characteristics	Double-end Polyether	Single-end Polyether
Thermal stability	Higher Capping reduces the risk of oxidative degradation	Lower Free hydroxyl groups are prone to oxidation
hydrolytic stability	Excellent Resistance to moisture attack	Poor Hydroxyl groups easily react with water
Compatibility with refrigerant	Wider Suitable for new type refrigerants like HFCs, CO2	Limited It's likely to react with some refrigerants.
lubricity	Excellent Stable molecular structure	Good It may degrade at high temperatures.
hygroscopicity	Extremely low Strong shydrophobic preperty	Higher Hydrophilic hydroxyl

 

 

Chorus can provide Di-Capped PAG for air conditioner compressor oil (AC refrigerant oils)

 

Synthetic polyethylene glycol (PAG) base oil with a double-ended structure is specially designed for air conditioner compressor oil and has a good compatibility with various HFC and HFO refrigerants (including R-404A, R-410A, R-407C, and R-1234yf). Compared with the uncapped-end PAG, the di-capped polyalkylene glycol has an excellent hydrolytic stability and low hygroscopicity, which can minimize potential issues associated with ice formation in capillary tubes and moisture-induced degradation. In the meantime, it can have an excellent compatibility with R-134a and other refrigerants within a wide range of operating temperatures. And the compatibility temperature is usually at -60°C to 0°C and 0°C to 80°C.

 

Chorus is a professional di-capped PAG supplier in China, and we can provide you with a perfect solution.