Section IV Fault Diagnosis
I. Fault diagnosis of system
i. Direct observation check
1. For checking faults like stop working or abnormal working of air conditioning system, some
apparent symptoms will appear by applying direct observation check. Direct observation check (of
looking, touching and listening) can diagnose faults accurately and easily, and quickly eliminate
faults.
(1) Carefully observe the existence of damage of pipelines, crack or oil stain on the surface of
condenser and evaporator. If oil stain exists on condenser, evaporator or their respective pipelines,
apply soap bubble leak detection. Key leak inspection areas include:
① Every joint of pipeline and every joint of valve;
② Joint between hoses;
③ Compressor oil seal, front and rear cover board, sealant pad, etc.
④ Scratch and deformation on the surfaces of condenser and evaporator;
(2) Observe the inspection window. Observing the inspection window of pipeline can check
refrigerant. Before observation, start engine and turn on air conditioning system, and make engine
work for 5 min at fast idle speed (1500~2000r/min). Then circulation condition of refrigerant can be
viewed through the inspection window:
① For normal circulation with one air bubble occasionally, refrigerant is in normal condition.
② For clarity and no bubble viewed, full refrigerant and no refrigerant can both be possible. If the
air outlet is cold, the refrigerant is in normal condition; if not, probably no refrigerant remains.
③ For relatively more bubbles, refrigerant is insufficient.
(3) Check electric circuits. Check whether disconnection of relevant circuits exists.
2. Check fault by touching with hands
(1) Check the high-pressure end of air conditioner refrigerating system. Switch on the air
conditioner; make refrigerating compressor work for 10~20min, touch pipelines and parts of the
high-pressure end of air conditioning system. From compressor outlet → condenser → drying
chamber to expansion valve inlet, normally, temperature felt by touching should change from hot
to warm. If certain part in the middle of the process is especially hot, the heat emission of the part
is in poor condition; if the parts are cold, faults like blockage, no refrigerant, compressor stopping
working or working in poor condition or so forth might exist.
(2) Check the low-pressure end of air conditioner refrigerating system. Switch on the air
conditioner; make refrigerating compressor work for 10~20min, touch pipelines and parts of the
low-pressure end of air conditioning system. From condenser to compressor inlet, normally,
temperature felt by touching should change from cool to cold. If it is not cold or frost appears, the
refrigerating system is in abnormal condition.
(3) Check temperature difference at compressor outlet. Switch on the air conditioner; make
refrigerating compressor work for 10~20min, touch the two ends of compressor inlet and outlet.
Obvious temperature difference should exist between the high-pressure end and the low-pressure
end of compressor. If temperature difference is not obvious or no temperature difference exists,
probably no refrigerant exists or refrigerant is extremely insufficient.
(4) Check circuits. Check whether the wire connector is in good connection. No connector of air
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