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Fault Finding if temperature increases downstream of evaporator > < Checking air conditioner cooling output - vehicles with manually controlled air conditioner

A1

Fault Finding if readout does not match specification
   
Fault Finding if readout does not match specification
–  „Read measured values“ in air conditioner „Guided fault-finding“ function → Vehicle diagnostic tester.
–  Repeat the cooling output test → Chapter.
–  During the cooling output test, observe actuation of the air conditioner compressor regulating valve -N280-. Was this deactivated during the cooling output test (control current dropped below 0.50 A) ?
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yes
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no
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–  Interrogate the event recorder, rectify the problems relating to the entries displayed and erase the event recorder → Vehicle diagnostic tester.
–  „Read measured values“ in air conditioner „Guided fault-finding“ function → Vehicle diagnostic tester.
–  During the cooling output test, observe the pressure in the refrigerant circuit. Is there an increase in pressure in refrigerant circuit during cooling output test?
–  Read out the air conditioner compressor shut-off criteria and eliminate the cause of the shut-off → Vehicle diagnostic tester.
–  Repeat the cooling output test.
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yes
↓
↓
Continued → Anchor
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no
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–  The vehicle is to be taken to a workshop equipped with the necessary tools where the work can be performed by appropriately qualified personnel → Air conditioner with refrigerant R134a. Inform the workshop of the problems encountered.

Continuation of test: „Increase in pressure in refrigerant circuit“
   
–  Open the front lid.
–  Repeat the cooling output test → Chapter.
l  Operation of radiator fan -V7- (and -V177-) during cooling output test? Speed is governed by coolant temperature and pressure in refrigerant circuit (determined by engine control unit).
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yes
↓
↓
no
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–  Read out the pressure in the refrigerant circuit and actuation of the radiator fan → Vehicle diagnostic tester.
l  Operation of -V7- (and -V177-) at higher speed as pressure in refrigerant circuit increases?
–  Check actuation of -V7-, e.g. in „Final control diagnosis“ function → Vehicle diagnostic tester.
–  Service the actuation system for -V7- ( -V177-).
–  Repeat the cooling output test → Chapter.
↓
yes
↓
↓
no
↓
 
–  The vehicle is to be taken to a workshop equipped with the necessary tools where the work can be performed by appropriately qualified personnel → Air conditioner with refrigerant R134a. Inform the workshop of the problems encountered.
–  Check actuation of -V7-, e.g. in „Final control diagnosis“ function → Vehicle diagnostic tester.
–  Service the actuation system for -V7-.

  Note
t  The pressure in the refrigerant circuit depends on various influencing factors. In general, however, the pressure should not exceed 20 bar at an ambient temperature of 20 to 25 °C. Under extreme usage conditions, e.g. in hot countries with high ambient temperatures, „stop and go traffic“ and high relative humidity, the extremely high cooling output involved may also result in pressures of up to 31 bar.
t  At ambient temperatures below 25 °C the pressure in the refrigerant circuit does not usually rise above 16 bar (radiator fan running and cooling condenser).
t  Depending on the pressure measured, the air conditioning system control unit -J301- actuates the air conditioner compressor regulating valve -N280- and requests the engine control unit to actuate the radiator fan -V7- by way of the data bus.
t  At absolute pressures of less than approx. 1.2 bar or greater than approx. 32 bar, -J301- does not switch on the air conditioner compressor ( -N280- is not actuated). The air conditioner compressor is only re-activated once the absolute pressure measured has risen above 1.8 bar or dropped below 16 bar.
t  To prevent abrupt deactivation of the air conditioner compressor on account of excessive pressure in the refrigerant circuit or an excessively high coolant temperature, its output is reduced by -J301- as soon as the pressure in the refrigerant circuit exceeds 30 bar (absolute) or the coolant temperature reaches 115 °C. Full air conditioner compressor output is not enabled again until the pressure has dropped below 27 bar. If the coolant temperature exceeds 115 °C, the output of the air conditioner compressor is further reduced by way of -J301-. The compressor is completely shut down at 118 °C.
t  If the pressure in the refrigerant circuit has exceeded 32 bar, -J301- does not switch the air conditioner compressor back on until the pressure has dropped below 29 bar.
t  Further information on the pressure in the refrigerant circuit can be found in the „Guided fault-finding“ → Vehicle diagnostic tester.
t  Depending on the vehicle model, a radiator fan 2 -V177- may also be fitted → Rep. gr.19.
   

Fault Finding if temperature increases downstream of evaporator > < Checking air conditioner cooling output - vehicles with manually controlled air conditioner