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Measures to be taken in the event of temperature increase downstream of evaporator > < Checking cooling output

A3 Mk2

Measures to be taken if readout does not match specification
   
Measures to be taken if readout does not match specification
–  Select the „Reading measured value block“ function → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  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, eliminate any faults displayed and erase the event recorder → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  Select the „Reading measured value block“ function → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  Observe the pressure in the refrigerant circuit during the cooling output test. Increase in pressure in refrigerant circuit during cooling output test?
–  Read out the compressor shut-off criteria and eliminate the cause of deactivation → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  Repeat the cooling output test.
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yes
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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(s) -V7- 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
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no
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–  Read out the pressure in the refrigerant circuit and actuation of the radiator fans → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
l  Operation of radiator fan(s) -V7- at higher speed as pressure in refrigerant circuit increases?
–  Check actuation of the radiator fans -V7-, e.g. in the „final control diagnosis“ function → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  Service the radiator fan -V7- actuation system.
–  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 the radiator fan(s) -V7-, e.g. in the „final control diagnosis“ function → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  Service the radiator fan -V7- actuation system.

  Note
t  The pressure in the refrigerant circuit is governed by various factors of influence. As a general rule, 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 (the radiator fan runs and cools the 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 fans -V7- by way of the data bus.
t  At absolute pressures of less than approx. 1.2 bar or greater than approx. 32 bar, the air conditioning system control unit -J301- does not switch on the air conditioner compressor (the air conditioner compressor regulating valve -N280- is not actuated). The air conditioner compressor is only switched on again 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 the air conditioning system control unit -J301- as soon as the pressure in the refrigerant circuit exceeds 30 bar (absolute) or the coolant temperature reaches 115 °C. Full 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, the air conditioning system control unit -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“ routine → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
   

Measures to be taken in the event of temperature increase downstream of evaporator > < Checking cooling output