| Fault Finding if ice forms at evaporator |
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| The air conditioner compressor regulating valve -N280- is actuated by the operating unit, Climatronic control unit -J255- or by the air conditioning system control unit -J301- 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 75 % (0.55 A) is displayed in the Read measured values function for the operating unit, Climatronic control unit -J255- or the air conditioning system control unit -J301- for actuation of the air conditioner compressor regulating valve -N280- depending on the measured temperature, engine speed and electrical system voltage
„Guided fault-finding“ function → Vehicle diagnostic tester. As soon as the temperature measured by the evaporator output temperature sender -G263- approaches the specified value, actuation is cancelled and the air conditioner compressor output thus reduced. |
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| Under certain operating conditions, residual moisture in the refrigerant circuit may lead to the formation of ice at the compressor regulating valve (and 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/heating output) after a lengthy journey; operation of air conditioner soon returns to normal after switching off 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 for example on vehicles with automatically controlled air conditioner; the air conditioner functions properly again after a short delay following engine shut-off. |
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| Check the measured value of the evaporator output temperature sender -G263- in the
„Guided fault-finding“ function → Vehicle diagnostic tester. |
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| If the sender measured value 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 the evaporator output temperature sender -G263- (an incorrect measured value can cause the evaporator to ice up). |
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| If the measured value for the sender 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 must be taken to a workshop which is equipped with the necessary tools and at which the work can be performed by appropriately qualified personnel → Air conditioner with refrigerant R134a. Inform the workshop of the problem detected. |
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| Check refrigerant pipe from evaporator (from expansion valve) to air conditioner compressor (thick pipe, low-pressure side) with engine running. If this pipe is severely iced up when problem occurs (thin layer of ice is permissible), this also indicates that evaporator temperature is too low. The vehicle must be taken to a workshop which is equipped with the necessary tools and at which the work can be performed by appropriately qualified personnel → Air conditioner with refrigerant R134a. There may be problems with air condtioner compressor control. Inform the workshop of the problem encountered. |
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