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Fault location for temperature rise downstream of evaporator > < Checking

A2

Fault determination in the event of deviation from specification
   
Fault determination in the event of deviation from specification
–  Select the display group “001” → Chapter in the “Read measured value block” function → Chapter
–  Repeat the refrigeration capacity test → Chapter.
–  During the refrigeration capacity test, monitor the display in zones “1” and “4”. Has the actuation of the air conditioner compressor regulating valve -N280- been deactivated during refrigeration capacity test (drop in control current to below 0.7 A )?
↓
yes
↓		↓
no
↓
–  Interrogate the fault memory → Chapter, rectify the faults displayed and erase the fault memory → Chapter.
l  Increase in pressure in the refrigerant circuit (display zone “4”) during the refrigeration capacity test?
–  Read the measured value block, display group “002” (compressor shutoff criteria) and eliminate the cause of the shutoff → Chapter.
↓
yes
↓		↓
no
↓
–  Repeat the refrigeration capacity test.
↓
Continued → Anchor
(Next table)
t
–  Take the vehicle to a specialist air conditioning workshop (fault in the refrigerant circuit).

   
Test contd.- The pressure in the refrigerant circuit rises
–  Remove the bonnet.
–  Repeat the refrigeration capacity test → Chapter.
l  Is the radiator fan -V7- running at stage 1 during the refrigeration capacity test?
↓
yes
↓		↓
no
↓
–  Read the measured value block, display group “001”, zone “1” (pressure in the refrigerant circuit) → Chapter.
l  Is the radiator fan -V7- switched to the 2nd stage as soon as the pressure in the refrigerant circuit exceeds 16 bar (absolute).
–  Check the actuation of the radiator fan -V7- → Anchor. (Final control diagnosis)
–  Service the actuation of the radiator fan -V7- in accordance with the circuit diagram.
–  Repeat the refrigeration capacity test → Chapter.
↓
yes
↓		↓
no
↓		 
–  Take the vehicle to a specialist air conditioning workshop (fault in the refrigerant circuit).
–  Check the actuation of the radiator fan -V7- → Anchor (Final control diagnosis)
–  Service the actuation of the radiator fan -V7- in accordance with the current flow diagram.

  Note
t  The pressure in the refrigerant circuit is influenced by various factors. In general, however, the pressure should not exceed 20 bar at an ambient temperature of 20 to 25 °C. Under extreme conditions of use (e.g. in hot countries with high ambient temperatures, “stop and go traffic” and high relative humidity), the extremely high refrigeration capacity 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 -V7- runs at stage 1 and cools the condenser). The air intake ducts in the front bonnet and the bumper may be closed off briefly in order to cause the pressure to rise to 16 bar until the cut-in pressure of the 2nd stage of the radiator fan -V7-.
t  The operating and display unit for air conditioner/Climatronic -E87- calculates the pressure in the refrigerant circuit via the signal ratio (display zone “3”).
t  At a signal ratio of less than 12.5 % (corresponds to approx. 1.5 bar absolute) and greater than 87.5 % (corresponds to approx. 32 bar absolute), the operating and display unit for air conditioner/Climatronic -E87- does not switch on the compressor (the air conditioner compressor regulating valve -N280- is not actuated). The compressor is only reactivated once the signal ratio exceeds 12.5 % (corresponding to an absolute pressure of 1.5 bar) or drops below 84 % (corresponding to an absolute pressure of 29 bar).
t  In order to prevent abrupt compressor shutoff on account of excessive pressure in the refrigerant circuit or an excessive coolant temperature, the compressor output is reduced by the operating and display unit for air conditioner/Climatronic -E87-:
t  - As soon as the pressure in the refrigerant circuit exceeds 30 bar (absolute pressure), (the full compressor output is not released again until the pressure has dropped below 27 bar).
t  - As soon as the coolant temperature exceeds 115° C (it is shut down completely at 118° C).
t  If the pressure in the refrigerant circuit had been in excess of 32 bar (signal ratio greater than 87.5 %), the operating and display unit for air conditioner/Climatronic -E87- would not have re-activated the compressor until the pressure had dropped below 29 bar (signal ratio less than 84 %).
t  You can find further information on the pressure in the refrigerant circuit in → Chapter (“Read measurement value block”, display group “001”)
   

Fault location for temperature rise downstream of evaporator > < Checking