| Fault localisation in the event of ice formation at the evaporator |
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| The electrical air conditioner compressor -V470- is actuated via the control unit for air conditioning compressor -J842- 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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| A value greater than 4000 rpm is displayed after switching on the ignition and depending on the vehicle speed, measured temperature and vehicle 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. |
| The following problems may be encountered if the measured value of the evaporator output temperature sender -G263- is incorrect (too high): |
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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), check actuation of electrical air conditioner compressor -V470- and refrigerant shut-off valve 1 for hybrid battery -N516- by battery regulation control unit -J840-. If, for example, -N516- is not actuated correctly when hybrid drive is active (no actuation despite only drive battery -A2- cooling being required), the evaporator in the air conditioning unit may ice up. |
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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 / air conditioner compressor 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. Check the measured value of the evaporator output temperature sender -G263- as well as the actuation and operation of the electrical air conditioner compressor -V470-, the refrigerant shut-off valve 1 for hybrid battery -N516-, the refrigerant shut-off valve 2 for hybrid battery -N517-, the control unit for air conditioning compressor -J842- and the battery regulation control unit -J840-. Take the vehicle to a workshop equipped with the necessary tools where the work can be performed by appropriately qualified personnel if a fault is found on -V470-, -N516-, -N517- or -J842- → "Guided Fault Finding" function of vehicle diagnostic, testing and information system VAS 5051 and → Air conditioner with refrigerant R134a. Inform the workshop of the problems encountered. |
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