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How to inspect the refrigeration oil volume in air conditioning compressor 
The vehicle air conditioning compressor is a high-speed operation device. Its normal condition depends on the 
sufficiency of the refrigeration oil, however excess refrigeration oil will influence the refrigerating effect. Oil 
volume inside the compressor must be checked when the compressor or part of the refrigeration system are 
replaced. The inspection methods are as follows:   
Fig.4-5 shows the inspection to the refrigeration oil volume. Discharge the oil charge plug 1, watch it via the oil 
charge taphole and rotate the clutch foreplate; Wipe clean the oil dipstick with the cotton yarn and insert it into 
the compressor until end of the oil dipstick touches inner casing of the compressor; take out the oil dipstick and 
observe its immersion depth; oil level inside the compressor shall be between scale 4 and scale 6 if the oil 
charging is appropriate. Add it if it is inadequate and drain if it is excessive, then tighten the filling port plug.   

 

Fig. 4-5    inspection to the refrigeration lubrication oil volume of the sedan air conditioning compressor 

1- oil filling plug 2- Filling port 3- oil dipstick 

Provided there is no oil filling plug hole in the compressor, the oil shall be poured into a measuring cup to 
make the comparison with the oil charge volume specified in the instruction to judge if the compressor is 
required to add the oil. Generally oil content in the compressor shall not be less than 1/3 oil charging volume 
specified in the instruction, or else the oil shall be added. Compressor provided with the oil charging plug hole 
can also adopt this method, but the compressor assembly must be removed from the air-conditioning system. 

 
 

 

 

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Fig 4-6 Refrigerant filling valve 

1 refrigerant reservoir 2 plate nut 3 upper connector of filling valve 

4 rotation lever 5 valve pin 

 
How to add the refrigerant to the vehicle air conditioning 
When the pressure in the refrigeration system is abnormal, the bubble will appear in the sight glass. It means 
the refrigerant is inadequate and shall be added; The vacuumizing is not required when adding the refrigerant. 
The refrigeration system can be added directly with the operational methods as follows:   
Connect both high and low pressure hoses of the manifold pressure gauge with interfaces of the high and low 
pressure charging valves; connect the intermediate hose of the manifold pressure gauge with the refrigerant 
cylinder valve. Carry it out according to the operation method related to 4.8. Close the manual high and low 
pressure valves and upright the refrigerant cylinder, then start the engine and turn on the air conditioning 
compressor 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 specified volume, close the manual low pressure valve and the refrigerant cylinder valve.   
How to check and eliminate the blocking failure of air-conditioning system 
When the refrigeration system is blocked, it shows inadequate refrigerant volume or no refrigerating, and 
meanwhile high pressure and low pressure inside the system are abnormal.    The block often occurs at the 
liquid storage dryer and the expansion valve. Temperature difference of the part before and after the blocking 
is apparent. The dirty block failure can be eliminated according to the following method:   
1). Drain out the refrigerant inside the refrigeration system.   
2). Remove the blocked part of the refrigeration system for the cleaning and the replacement.   
3). When there is severe block, the refrigeration system shall be dismantled entirely for subsection cleaning. 
Spares after the cleaning shall be blown-dried and oven-dried.   
How to check and eliminate the icing failure of vehicle air-conditioning thermo expansion valve 
The system is poor in the refrigerating effect and low bias in both high and low pressure after the refrigeration 
system is iced; the refrigeration is intermittent. The icing generally occurs at the valve seat of the thermo 
expansion valve because excessive water vapor contained in the system is iced at valve base of the thermo 
expansion valve.  When the thermo expansion valve occurs ice block, the refrigerating capacity will be 
reduced that causes the temperature rise to melt down the ice at the valve port so the system recovers normal 
operations to increase the refrigerating capacity, at that time excessive moisture will be iced again at the valve 
port. Methods of eliminating the icing failure of the refrigeration system are as follows:   
1). Drain out the refrigerant inside the system.   
2). Replace the dry reservoir in the refrigeration system.   
3). Inspect the refrigeration system for any leakage and stop it.   
4) Make the vacuumizing with the vacuum pump and remove the water vapor inside the system.   
5) Add qualified refrigerant.   
How to check and eliminate the air inside the air-conditioning system 
Air in the system is stored at upper part of the condenser or the dry reservoir owing that it is incapable of being 
condensed and is lighter than the refrigerant. Air in the system will influence the cooling and heat emission 

 
 

 

 

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effect of the condenser thus cause the condensing pressure and temperature over high, simultaneously low 
pressure of the system is high that causes the refrigerating capacity of overall system being reduced, so that 
air in the system shall be removed timely with the preclusion methods as follows:   
1). Drain out the refrigerant inside the system.   
2). Inspect the refrigeration system for any leakage and eliminate it.   
3). Pump out the air in the system repeatedly with the vacuum pump.   
How to dismount the sedan air conditioning compressor   
When the air conditioning compressor is breakdown, most failure parts shall be dismounted to carry out the 

repair or the replacement except very few failure parts can be maintained on the vehicle instead of 

dismounting the compressor. The dismounting steps and requirements are as follows:   
Steps of dismounting the compressor from the compressor frame:   
(1). Dismount the connecting wire of the electromagnetic clutch.   
(2) Drain out the refrigerant from the refrigeration system.   
(3) Remove the hoses at intake and exhaust port of the compressor; the hose as well as intake and exhaust 
ports of the compressor shall be covered to prevent the dust and the water vapor from being entered into the 
system.  
(4) Dismount the driving belt of the compressor.   
(5) Remove the compressor fastening screw and the compressor from the compressor frame.   
(6) Pour out the oil inside the compressor and measure the oil output with the measuring cylinder to judge if it 
is required to add the oil and inspect the oil for any discoloration as well as any impurities in the oil.   
Inspection to the air conditioning control system 
The air conditioning control system can be checked according to the following methods: power→ ignition→ 
switch→ fuse cutout→ relay→ air conditioning switch ( fan switch, temperature detect switch)→temperature 
control circuit→pressure switch circuit→electromagnetic clutch→fan→electric machine. After the ignition 
switch is turned on, the current flows into the air conditioning switch through the fuse cutout and is branched. 
One branch flows into the evaporator blower motor and the other branch flows into the compressor 
electromagnetic clutch through the temperature controller and the pressure switch circuit.    When malfunction 
is found in the auto security protection, the fuse shall be checked first for any burn-out; If it is in normal 
condition, control switch of the blower shall be turned on to inspect if the blower plug is in good contact, the 
blower governing resistance is in open circuit and the blower motor is damaged; If the blower is in normal 
operation, then finally check the control circuit of the electromagnetic clutch, the high and low pressure switch, 
the temperature controller as well as the electromagnetic clutch for any failure; eliminate any failure existed. 

How to inspect the vehicle air conditioning thermo expansion valve 
Inspection steps of the vehicle air conditioning expansion valve (take F type thermo expansion valve as an 
example) are as follows:   
1). Eliminate the refrigerant in the system and remove the thermal expansion valve from the refrigeration 
system.  
2). Supply the nitrogen with certain pressure (e.g. 0.05Mpa) at the high pressure inlet side of the thermal 
expansion valve. If there is no gas flowing out from the low pressure outlet side, it means the thermal 
expansion valve is out of service.   
3). Then immerse the thermo bulb of the thermal expansion valve into warm water and enhance the water 
temperature; opening of the thermal expansion valve shall be increased (pressure at the low-pressure side is 
increased, i.e. the gas flow rate is increased), or else it means media inside the thermal expansion valve power 
head is leaked or the thermal expansion valve is blocked by impurities, then the thermal expansion valve shall 
be replaced.   
4) The blocked thermal expansion valve shall be disassembled to determine the impurity nature.   
Other notices in repairing the vehicle air conditioning 
1). Operation environment: cleanness and moistureproof shall be paid attention to when the air conditioning is 

 
 

 

 

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checked. Dirt, dust and moisture shall be prevented from entering into the air-conditioning system. Areas 
around the assembling unit and the joint shall be cleaned out and rainy day maintenance shall be avoided.   
2). Usage of the refrigerant: the refrigerant shall be stored in places of low temperature and dry when the 
refrigerant cylinder is stored and transported. It shall not be brought into locations with open flame such as the 
welding, nor exposed under the sunshine. Directly heating to the refrigerant cylinder or putting it into the hot 
water over 40 Celsius degree is strictly prohibited. The protective glasses shall be worn when the refrigerant is 
filled to avoid the eye frost damage. Please be noted that it shall not be contact with the skin. Provided the 
refrigerant is contacted with accidentally, a great deal of fresh water shall be used to rinse the contact area 
quickly to prevent the frost damage and ask for medical care as soon as possible. Manual high pressure valve 
on the manifold pressure gauge is strictly prohibited to open when the engine is in operation. The refrigerant 
will back flow into the refrigerant tank that cause the explosion. When the gaseous state refrigerant is charged 
from the low pressure side during the engine running, the refrigerant cylinder is not allowed to upend to avoid 
the compressor "cylinder slugging". The manifold pressure gauge shall be used to drain out the refrigerant 
inside the system from the low pressure side. The refrigerant shall be exhausted slowly with the time interval 
not less than 15 minutes to prevent the refrigeration oil from being drained out along with the refrigerant.   
3). Operation to the refrigeration system pipeline: the pipeline or the joint shall be capped after the pipeline is 
dismounted to prevent the moisture and the dust from entering into it. The bending radius shall be as large as 
possible when the pipe is bent; the pipe orifice shall be remained leveling and clean when the pipe is cut and 
scraps inside the pipe shall be cleaned out; The trichloroethylene liquid shall be used to clean the pipeline, and 
the pipeline shall be dried sufficiently; The refrigeration oil shall be applied at the joint and the O-ring when the 
pipeline is connected; two wrenches shall be used to tighten or unscrew the pipeline joint.   
4). Operation to the control wire: the battery ground wire (negative wire) shall be dismounted when the repair 
work is made to the air conditioning to prevent the circuit short circuit during the refrigeration system repair. 
Replaced wires shall be fixed by the adhesive tape and the original fasteners; wires of original color and 
original diameter shall be preferred; the wire is not allowed to close to high temperature objects such as the 
engine.  
There is several methods of judging the constant malfunction of the vehicle air conditioning as follows:   
1). Hand feeling inspection: the failure is judged mostly by feeling the temperature of the parts by hand. High 
pressure loop (from the compressor outlet, the condenser and the dry reservoir to the thermal expansion valve 
outlet) shall be in a thermal behavior (50 ~ 70 ) when it is touched; 

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if certain location is exceptionally hot or 

there is apparent temperature difference between the inlet and the outlet, it means there is the blocking. The 
low pressure loop (from the thermal expansion valve outlet, the evaporator and the compressor inlet) shall be 
cool (0 ~ 5 ) when it is touched. Provided there is no apparent temperature difference between the high 

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℃

pressure side and the low pressure side, it means there is the leakage in the system or the compressor is 
broken down.   
2). Visual examination: inspect each pipeline joint, compressor shaft seal, condenser and evaporator surface 
for any oil stain; the system has the leakage if there is any oil stain.   
3). Sight glass inspection: observe and inspect the refrigerant state via the sight glass installed on the dry 
reservoir or the pipeline. The refrigerant shall be clear and bubble free, and the evaporator air outlet shall be 
cold under normal condition. It means that the refrigerant is highly inadequate when it is clear and bubble free 
yet the air outlet is not cold; is means that the refrigerant is inadequate when it is clear and has bubble in it, yet 
the air outlet is not cold enough.   
4). Leak detection made by the electronic leak detector:    electronic leak detector is used to inspect each joint 
of the overall system for any leakage.   
5). Inspection made by the multi-meter: the multi-meter can be used to check out the air conditioning circuit 
breakdown and judge the broken circuit or the short circuit.   
6). Manifold pressure meter: connect the manifold pressure meter with the system high and low pressure