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

A1

Measures to be taken if readout does not match specification
   
Measures to be taken 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
↓
↓
no
↓
–  Interrogate the event recorder, rectify the problems relating to the entries displayed and erase the event recorder → Vehicle diagnostic tester.
l  Increase in pressure displayed as measured value 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
↓
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.

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? The speed is governed by the coolant temperature and the pressure in the refrigerant circuit; it is detemined by the engine control unit.
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yes
↓
↓
no
↓
–  Read out the pressure in the refrigerant circuit and actuation of the radiator fan → Vehicle diagnostic tester.
l  Operation of -V7- at higher speed as pressure in refrigerant circuit increases?
–  Check actuation of -V7- (and -V177-), 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, or 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  The operating unit, Climatronic control unit -J255- uses the duty cycle to calculate the pressure in the refrigerant circuit.
t  If the duty cycle is less than 10 % (corresponding to approx. 1.2 bar absolute pressure) and greater than 78 % (corresponding to approx. 32 bar absolute pressure), the operating unit, Climatronic control unit -J255- does not switch on the air conditioner compressor (the air conditioner compressor regulating valve -N280- is not actuated). The air conditioner compressor is only re-activated once the duty cycle exceeds 12 % (corresponding to absolute pressure of 1.8 bar) or drops below 48 % (corresponding to absolute pressure of 16 bar).
t  To prevent abrupt air conditioner compressor shut-off on account of excessive pressure in the refrigerant circuit or excessive coolant temperature, the compressor output is reduced by the operating unit, Climatronic control unit -J255- as soon as the pressure in the refrigerant circuit exceeds 30 bar (absolute). Full air conditioner compressor output is not enabled again until the pressure has dropped below 27 bar or the coolant temperature exceeds 115 °C (complete shut-off at 118 °C).
t  If the pressure in the refrigerant circuit had been in excess of 32 bar (duty cycle greater than 78 %), the operating unit, Climatronic control unit -J255- does not re-activate the air conditioner compressor until the pressure has dropped below 29 bar (duty cycle less than 74 %).
t  Further information on the pressure in the refrigerant circuit can be found in the „Guided fault-finding“ function → 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 automatically controlled air conditioner