| Fault localisation in the event of ice formation at the evaporator |
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| The air conditioner compressor regulating valve -N280- is actuated by the air conditioner operating and display unit, Climatronic control unit -J255- such that the temperature of the air downstream of the evaporator reaches the specified value (approx. 2 to 5 °C). |
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| After starting the vehicle, a value greater than 0.55 A is displayed depending on the measured temperature, engine speed and electrical system voltage. As soon as the temperature measured by the evaporator output temperature sender -G263- approaches the specified value, actuation is cancelled and the compressor output thus reduced. |
| Under certain operating conditions, residual moisture in the refrigerant circuit may lead to the formation of ice at the air conditioner compressor regulating valve -N280- (and at the expansion valve). Such ice formation impedes air conditioner compressor control. The evaporator is excessively cooled and ices up. Icing-up of the evaporator may give rise to the following problems: |
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| Repeated or sporadic failure of the air conditioner (no cooling/heat output) after a lengthy journey; operation of the air conditioner soon returns to normal after switching off the engine. |
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| Misting up of the windows on the inside after a long journey; the windows are initially not cleared even by pressing the „Defrost“ button of the air conditioner operating and display unit, Climatronic control unit -J255-; the air conditioner functions properly again after a short delay following engine shut-off. |
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| If the measured value of -G263- is too high under the usage conditions described by the customer (greater than e.g. 10 °C although the air conditioner is functioning properly, depending on ambient temperature), check -G263- (an incorrect measured value can cause the evaporator to ice up). |
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| If the measured value for -G263- is too low under the usage conditions described by the customer (at ambient temperature above 0 °C, colder than 0 °C for lengthy period): 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. |
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| Check the „low-pressure end“ refrigerant line (thick line between quick-release coupling and air conditioner compressor) → Chapter with the engine running. If this line is severely iced up when the problem occurs (a thin layer of ice is permissible), this is also an indication that the temperature in the evaporator is too low. 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 (there may be problems with air conditioner compressor control). Inform the workshop of the problems encountered. |
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