389 

 

Open    Open 

Fig 4-2 Structure of manifold pressure gauge 

1 high pressure gauge 2 low-pressure gauge, 3 manual low pressure valve, 4 manual high-pressure valve, 5 

valve body, 6 high pressure connection, 7 refrigerant vacuumizing connector 

8 low-pressure connector 

Usage of the refrigerant charging valve 
A charging valve is installed on the inlet and the exhaust pipes of the sedan air conditioning compressor. Its 
operating principle is identical to that of the valve core on the tire. During the usage, tighten the quick joint of 
the charging hose into the port of the charging valve so that the needle is pressed open; the air-conditioning 
system is connected with the detection used hose with the refrigerant flows into it; the charging valve can be 
closed automatically when the detection used hose is removed.   
Routine method to check the leakage of air conditioning refrigerant 
Leak-detection methods generally used in the vehicle air conditioning refrigeration system are nitrogen 
supercharging leak detection, vacuum leak detection, charging leak detection, instrument leak detection and 
appearance leak detection.   
1). Nitrogen supercharging leak detection: charging the nitrogen into the refrigeration system and apply the 
soap water at the leak detection position. The soap bubble will be generated when there is the leakage. The 
compressed air is strictly prohibited when the supercharging leak detection is adopted. This is because there is 
moisture in the compressed air and will cause the ice block at the thermal expansion valve when the moisture 
enters into the system along with the air. The industry nitrogen is non-corrosive, moisture-free and low in price, 
yet bottle high pressure nitrogen gas must be provided with a decompression adjuster to adjust the air out 
pressure. When the system reaches the specified 1.0 Mpa, apply the soap bath at each joints and welding 
points of the system to observe the leakage carefully. There is tiny sound at large leakage area with big foam 
and there is discontinuous small foam at small leakage area. The leak detection must be made carefully and 
repeated for 3 to 5 times. The leaking position shall be marked and restored in time, then the leak detection 
can be made at other joints until the leakage is eliminated totally. The leak-off-test shall be made after the 
leakage is restored, i.e. the system is kept the pressure for more than 0.5 hours. The leak-off-test is accepted 
when the pressure does not reduce; the leak detection must be made once again if the pressure reduces 
greatly until the leaking area is found and restored.   
Leak-off-test pressure of the refrigeration system is 1.5 ~ 1.7Mpa. Take care when checking the leak.   
2). Vacuum leak detection: it shall be made adopting the vacuum pump. The vacuum pressure shall be lower 
than 100Pa and constant. It is acceptable when the vacuum pressure is not increased remarkably during 
relatively long time.   
3). Filling leak detection: it can be made following the vacuum leak detection. The leak detection is carried out 
by the electronic leak detector after little refrigerant is charged. The indicator will light up and give out an alarm 
when the refrigerant is leaking.   
4). Appearance leak detection: normally there is the refrigeration oil leaked out at the refrigerant leaking 

 
 

 

 

390 

locations. A clean plain paper can be used to wipe it off or the hand can be used to inspect it directly. It means 
the refrigerant leakage when the oil stain keeps on leaking.   
Locations where air conditioning refrigerant leakage often occurs   
Operating condition of the air conditioning is normally rough. Its refrigeration system keeps on vibrating along 
with the vehicle operation, hence the pipeline is easy to be damaged and the joint is loose thus causing the 
refrigeration leakage. The general leaking locations are shown as the following table.   

Locations where air conditioning refrigerant leakage often occurs 

Assembly Leaking 

parts 

Connection of the condenser air inlet pipe and the liquid outlet pipe 

Condenser 

Welding of the condenser flat pipe and the collector pipe 

Connection of the evaporator air inlet pipe and the liquid outlet pipe 

Evaporator 

Each welding of the evaporator 

Thermo expansion valve 

Gas phase head 

Fusible plug 

Liquid storage dryer 

Connection of the evaporator liquid inlet pipe and the liquid outlet pipe 

High and low pressure hoses 

Refrigerant line 

Connections of high and low pressure hoses 

Compressor shaft seal 

Connection of inlet and outlet 

Sealings of front and rear cover 

Compressor 

Air intake and exhasut valves of the compressor 

How to carry out the vacuumizing, leak detection and refrigerant filling to the vehicle air conditioning 
There are three purposes of making the vacuumizing by the vacuum pump: the first, to drain out the air and the 
moisture in the air-conditioning system; the second, to inspect the leakage in the system; the third, to dry the 
system. The refrigerant can be filled only after the system is vacuumized. The vacuumizing can reduce the 
boiling point rather than drain the water out from the refrigeration system directly after the vacuum is realized. 
The water is drained out from the refrigeration system only after it is transferred into the water vapor. 
Connection of the vacuumizing pipeline is shown in Fig.4-3. Detailed steps are as follows:   
1). Connect both high and low pressure hoses of the manifold pressure gauge with high and low pressure 
charging valve interface of the system (note: for the sedan air-conditioning system, most high and low pressure 
charging valves are on the high and low pressure hoses, while very few hoes are on the compressor); connect 
the intermediate hose on the manifold pressure gauge with the vacuum pump.   
2). Open the manual high and low pressure valves on the manifold pressure gauge and start the vacuum pump; 
vacuumize the systemic pressure to below 100pa and keep constant.   
3). Close the manual high and low pressure valves on the manifold pressure gauge and see if the pressure 
shown by the gauge indicator is recovered; the pressure recover means the system leakage, then the leak 
detection and repair shall be made by this time. Provided the gauge indicator keeps still, the hand valve shall 
be opened to startup the vacuum pump and keep on vacuumizing until pointer of the if is constant.   
 
 

 
 

 

 

391 

 
 
 
 
 
 
 
 
 
 
 
 
 

 

 

 

1 compressor     2 vacuum pump     3 air     4 low pressure gauge 

5 high pressure gauge          6 manual low pressure valve opening 

7 manual high pressure valve opening 

Fig 4-3 Vacuumizing of air conditioning refrigeration system 

4). simultaneously close the manual high and low pressure valves after the vacuumizing.   
5). Screw down the intermediate hose of the manifold pressure gauge from the vacuum pump joint and switch 
over a refrigerant cylinder joint.   
6). Unscrew the intermediate hose joint on the manifold pressure gauge and slightly open the refrigerant 
cylinder valve to send away the air in the intermediate hose by the refrigerant. It is OK just being opened for 
2~3 seconds.   
7). Open the manual high and low pressure valves and the refrigerant cylinder valve so that small volume of 
the refrigerant can enter into the refrigeration system until the gauge indicator points into 1000pa. Close the 
manual high and low pressure valve as well as the refrigerant cylinder valve and remain for several hours.   
8). If there is no variation in the systemic pressure, it means the system has no leakage; provided the systemic 
pressure is reduced, it means there is leakage in the system, then the leaking location shall be found out and 
precluded.  
9). Open the refrigerant cylinder valve and the manual high-pressure valve so that the refrigerant can be 
entered into from the high pressure side after the system is confirmed having no leakage. By this time the 
refrigerant cylinder can be inverted to increase the charging rate, however the air conditioning is not permitted 
to startup.   
10). The refrigerant can also be filled from the low pressure side. The method is that the manual high-pressure 
valve is closed and the refrigerant cylinder is kept upright, then the air conditioning compressor is turned on to 
operate. Slowly open the manual low pressure valve so that the refrigerant can enter into the suction 
compressor in gaseous state from the low pressure side; when the refrigerant charging volume achieves the 
requirement, the manual low pressure valve and the refrigerant cylinder valve are closed.   
11). Watch it from the sight glass to ensure there is no bubble or surplus refrigerant inside the system. Then 
adjust the engine speed to 2000r/min and turn the cold air machine air volume to the top gear. Provided the air 
temperature is between 30  and 35 , pressure at low pressure side of the system shall be about 0.15 ~ 

℃

℃

0.20Mpa and that at high pressure side shall be about 1.3 ~ 1.8Mpa.   
12). Stop the engine after the charging is finished. Remove the manifold pressure gauge from the compressor 
quickly to prevent surplus refrigerant from being discharged.   
Operation and notice of filling or adding the refrigeration oil to the air conditioning, judgment to the 
refrigeration oil quality 
1) Generally it is not required to fill the refrigeration oil when the air conditioning refrigeration system is 

 
 

 

 

392 

maintained. However, the refrigeration oil must be added when parts of the refrigeration system are replaced 
and severe leakage of the system is precluded. There are two methods to fill the refrigeration oil as follows: (1) 
Shut down the air conditioning and fill the refrigeration oil utilizing the filling port on the compressor; screw out 
the filling port bolt and pour the required refrigeration lubrication oil into the filling port and then tighten the 
filling port bolt.   

(2) Detailed operation methods of charging the refrigeration oil when the vacuumizing is made are as follows: 

 

 

Fig. 4-4    Filling the refrigeration lubrication oil with vacuumizing method 

1- the manual low pressure valve is closed    2- the manual high pressure valve is opened 

3- exhaust the air    4- vacuum pump 5- refrigeration lubrication oil 

a. Select a graduated cylinder to contain the refrigeration oil of the volume more than required.     
b. Screw down the hose connected with the low pressure charging valve from the manifold pressure gauge 
and insert it into the measuring cylinder containing the refrigeration oil. As shown in Fig.4-4.     
c. Startup the vacuum pump and open the manual high pressure valve on the manifold pressure gauge. Added 
refrigeration oil will be sucked into the compressor through the suction pipe via the charging valve at the low 
pressure side. Stop the suction of the vacuum pump and close the manual high pressure valve when the 
refrigeration oil volume has reached the specified volume.     
d. After the refrigeration oil is added per the vacuumizing method, the refrigeration system shall be vacuumized 
and the refrigerant shall be added.   
2) The following notices shall be taken care when the refrigeration oil is used: (1). The refrigeration oil is easy 
in water absorption so the lid must be tightened right after the refrigeration oil is used 
(2). Deteriorate turbid refrigeration oil is not allowed, or else it will influence the normal operation of the 
compressor.  
(3). Excess refrigeration oil is not allowed to be added into the system, or else it will influence the refrigerating 
capacity of the vehicle air conditioning refrigeration system.   
(4) The refrigeration oil must be of the grade specified in the compressor instruction of that model.   
3) Correlation method and dripping method can be adopted to judge the quality of the refrigeration oil:    (1). 
Correlation method: put clean and standard refrigeration oil into a test tube as the standard oil and put the oil to 
be checked into another test tube of the same size to make the comparison. Provided the oil to be checked is 
of light yellow or of saffron yellow, it can be used, however the turbid solution of rufous color can not be used.   
(2). Dripping method: drip one drib of the refrigeration lubrication oil to be checked on a clean plain paper and 
watch its color. It means there is no impurity in the oil if its color is light and even; the oil can be used.