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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017
♦ The refrigerant temperature sender (with temperature-de‐
pendent resistor) is installed e.g. in the high pressure line in
the vicinity of the air conditioner compressor.
♦ There is a direct correlation between temperature and pres‐
sure in the refrigerant circuit: if there is too little refrigerant in
the refrigerant circuit, the temperature in the refrigerant circuit
rises during operation of the air conditioning system on the
high pressure side greater than permitted for this pressure.
Note
The respective control unit, e.g. the operating and display unit for
lk
front air conditioning system - E87- or the Climatronic control unit
- J255- evaluates the pressure and the temperature in the refrig‐
erant circuit and switches off the air conditioner compressor if the
temperature increases above the value stored for this pressure
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode - air
conditioning system and ⇒ Heating, air conditioning; Rep. gr.
87 ; Refrigerant circuit (vehicle-specific workshop manual).
1.3
Possible complaints
⇒ “1.3.1 Prerequisites for investigating a complaint”, page 64
⇒ “1.3.2 Possible complaints”, page 64
⇒ “1.3.3 Odours from heater and air conditioner unit”, page 66
1.3.1
Prerequisites for investigating a com‐
plaint
•
No fault was evident during fault finding in the electrical sys‐
tem, vacuum system and air ducts/channels ⇒ Vehicle diag‐
nostic tester in “Guided Fault Finding” mode - air conditioning
system (and battery control), ⇒ Current flow diagrams, Elec‐
trical fault finding and Fitting locations and ⇒ Heating, air
conditioning; Rep. gr. 00 ; Repair instructions; Checking cool‐
ing output .
•
•
Self-diagnosis in “Guided Fault Finding” mode - air condition‐
ing system (e.g. using ⇒ Vehicle diagnostic tester in “Guided
Fault Finding” mode - air conditioning system) provides no
evidence of a complaint.
No shut-off condition for the air conditioner compressor is dis‐
played in the measured values of the control unit of the air
conditioning system ⇒ Vehicle diagnostic tester in “Guided
Fault Finding” mode - air conditioning system.
1.3.2
Possible complaints
Note
♦ For all complaints marked with *
⇒ “2.14 Checking pressures”, page 170 .
♦ If on vehicles with 2 evaporators a problem is encountered in
just one evaporator, check the pressures in the refrigerant cir‐
cuit as well ⇒ “2.14 Checking pressures”, page 170 .
♦ The cooling has failed completely.*
♦ Insufficient cooling output at all vehicle speeds and engine
speeds.*
♦ No or insufficient cooling after driving a few miles. *
64
Rep. gr.87 - Air conditioning system
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