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

A4 Mk2

Measures to be taken if readout does not match specification
   
Measures to be taken if readout does not match specification
–  In “Reading measured value block” function → Chapter, select display group “001” → Chapter.
–  Repeat cooling output test → Chapter.
–  During cooling output test, observe display in zones “1” and “4”. Actuation of air conditioning system compressor regulating valve -N280- deactivated during cooling output test (drop in control current to below 0.55 A )?
↓
yes
↓		↓
no
↓
–  Interrogate fault memory → Chapter, eliminate faults displayed and erase fault memory → Chapter.
l  Increase in pressure in refrigerant circuit (display zone “4”) during cooling output test?
–  Read measured value block, display group “002” (compressor shutoff criteria) and eliminate cause of shutoff → Chapter.
↓
yes
↓		↓
no
↓
–  Repeat cooling output test.
↓
Test continued (increase in pressure in refrigerant circuit) → Anchor
–  Take vehicle to specialist air conditioner workshop (fault in refrigerant circuit) → Note.

1)  If applicable, check again that compressor is actually being driven before taking vehicle to a specialist air conditioner workshop. On vehicles with 8-cyl. engine, the drive shaft may have become detached from the compressor drive unit for example → Chapter
Test continued (increase in pressure in refrigerant circuit)
   
–  Open bonnet.
–  Repeat cooling output test → Chapter.
l  Operation of radiator fan(s) -V7- during cooling output test (speed is governed by coolant temperature and pressure in refrigerant circuit; determined by engine control unit)?
↓
yes
↓		↓
no
↓
–  Read measured value block, display group “001” zone “4” (pressure in refrigerant circuit) → Chapter.
l  Operation of radiator fan(s) -V7- at higher speed with increase in pressure in refrigerant circuit → Chapter (reading measured value block, display group “014”)
–  Check actuation of radiator fan -V7-, perform final control diagnosis → Chapter.
–  Repair actuation of radiator fan(s) -V7-.
–  Repeat cooling output test → Chapter.
↓
yes
↓		↓
no
↓		 
–  Take vehicle to specialist air conditioner workshop (fault in refrigerant circuit).
–  Check actuation of radiator fan(s) -V7- → Chapter (perform final control diagnosis).
–  Repair actuation of radiator fan(s) -V7-.

  Note
t  The pressure in the refrigerant circuit is governed by various factors. In general, however, at an ambient temperature of 20 to 25 °C the pressure should not exceed 20 bar. Under extreme usage conditions (e.g. in hot countries with high ambient temperatures, “stop and go traffic” and high relative humidity), the high cooling output then required 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(s) -V7- run(s) and cool(s) condenser).
t  The duty cycle (reading measured value block → Chapter, display group “001”, display zone “3”) is used by the operating and display unit, Climatronic control unit -J255- to calculate the pressure in the refrigerant circuit.
t  If the duty cycle is less than 12.5% (corresponding to approx. 1.8 bar absolute pressure) and greater than 87.5% (corresponding to approx. 32 bar absolute pressure), the operating and display unit, Climatronic control unit -J255- does not switch on the compressor (the air conditioning system compressor regulating valve -N280- is not actuated). The compressor is only re-activated once the duty cycle exceeds 12.5% (corresponding to absolute pressure of 1.8 bar) or drops below 48% (corresponding to absolute pressure of 16 bar).
t  To prevent abrupt compressor shutoff on account of excessive pressure in the refrigerant circuit or excessive coolant temperature, the compressor output is reduced by the operating and display unit, Climatronic control unit -J255-:
t  - As soon as the pressure in the refrigerant circuit exceeds 30 bar (absolute) (full compressor output is not released again until pressure has dropped below 27 bar)
t  - As soon as the coolant temperature exceeds 115° C (full shutdown at 118° C)
t  If the pressure in the refrigerant circuit had been in excess of 32 bar (duty cycle greater than 87.5%), the operating and display unit, Climatronic control unit -J255- does not re-activate the compressor until the pressure has dropped below 29 bar (duty cycle less than 84%).
t  For further notes on pressure in refrigerant circuit, refer to → Chapter“Reading measured value block”, display group “001”.
   

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