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Possible deviation from specification | Possible causes of fault | Fault elimination | ||||||||||||||||||||||||||
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Observe notes → Anchor. |
Possible deviation from specification | Possible causes of fault | Fault elimination | ||||||||||||||||||||||||||||||
On vehicles without refrigerant shut-off valve 1 for hybrid battery -N516-
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On vehicles with -N516-
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t | If no fault is found for this problem, clean the refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter). Constriction or blockage in the refrigerant circuit may also lead to one of these problems |
t | Check the measured values of the evaporator output temperature sender -G263- and, if fitted, of the temperature sensor upstream of evaporator for hybrid battery -G756- and of the temperature sensor downstream of evaporator for hybrid battery -G757- as well as actuation of the air conditioner compressor by way of the control unit for air conditioning compressor -J842- by the battery regulation control unit -J840- → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner and battery regulation. |
t | An incorrect -G263-, -G756- or -G757- measured value may also cause problems with the cooling output or the evaporator may ice up. |
t | If, after renewing the expansion valve for example, operation of the air conditioner is not OK when the test is repeated (re-fit old expansion valve), clean the refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter). Then renew the air conditioner compressor and receiver/dryer cartridge. |
t | In the event of a fault at a temperature sensor, the evaporator may ice up although the quantity of refrigerant in the circuit is OK. |
t | If the expansion valve at the evaporator in the air conditioning unit or -N516- is defective (is permanently closed or does not open sufficiently), the air conditioner compressor is actuated to maximum output and the low pressure drops to the value in the graph or below (air conditioner compressor draws off refrigerant from low-pressure side). As however refrigerant cannot flow via the expansion valve, the cooling output is not attained and the high pressure may also not increase or only increase slightly due to the absence of energy conversion → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner and battery regulation and → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual). |
t | The output of the evaporator in the air conditioning unit is considerably higher than that of the evaporator in the battery cooling module. Depending on the version, the refrigerant shut-off valve 2 for hybrid battery -N517- at the expansion valve in the battery cooling module is currently only actuated by the battery regulation control unit -J840- in order to cool the drive battery -A2- (hybrid battery) only when the battery reaches a certain temperature; energy conversion via the evaporator in the battery cooling module is not increased or only slightly increased → Vehicle diagnostic tester in „Guided Fault Finding“ mode for air conditioner and battery regulation and → Air conditioning; Rep. gr.87. |
Possible deviation from specification | Possible causes of fault | Fault elimination | ||||||||||||||||||||||||||||||||
On vehicles with -N516-
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t | The refrigerant shut-off valve 2 for hybrid battery -N517- is currently only actuated by the battery regulation control unit -J840- in order to cool the drive battery -A2- (hybrid battery) when the battery reaches a certain temperature. If air conditioning mode has not already been activated at this point, the electrical air conditioner compressor -V470- is actuated via the control unit for air conditioning compressor -J842- by -J840-. The temperature of the air upstream and downstream of the evaporator in the battery cooling module is determined by -J840-. If it is established that the cooling action is not sufficient, this is stored in -J840- → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner, air conditioner compressor and battery regulation |
t | The temperature of the air (and thus the cooling output of the evaporator) in the battery cooling module is determined by way of built-in temperature sensors (at present it cannot be measured with a thermometer during operation) and can only be checked using the Guided Fault Finding routine → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner, air conditioner compressor and battery regulation. |
t | For further information, refer to → Anchor |
Possible deviation from specification | Possible causes of fault | Fault elimination | ||||||||||||||
On vehicles with refrigerant shut-off valve 1 for hybrid battery -N516-
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Possible deviation from specification | Possible causes of fault | Fault elimination | ||||||||||||||||||||||||||||||||||||
On vehicles without refrigerant shut-off valve 1 for hybrid battery -N516-
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On vehicles with -N516-
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t | If the operation of the air conditioner is not OK when the test is repeated, renew the expansion valve and receiver (and -N516- if fitted). |
t | In this case, the evaporator may ice up although the correct quantity of refrigerant is present in the refrigerant circuit. |
t | If the expansion valve at the evaporator in the air conditioning unit or -N516- is defective (is permanently closed or does not open sufficiently), the air conditioner compressor is actuated to maximum output and the low pressure drops to the specified value or below (air conditioner compressor draws off refrigerant from low-pressure side). However, as refrigerant cannot flow via expansion valve -N516-, cooling output is not attained and high pressure may also not increase or only increase slightly since there is no energy conversion → Vehicle diagnostic tester in „Guided Fault Finding“ mode for air conditioner and battery regulation and → Air conditioning; Rep. gr.87 (vehicle-specific Workshop Manual). |
t | If the expansion valve at the evaporator in the battery cooling module is defective (or refrigerant shut-off valve 2 for hybrid battery -N517- is not operating or is not actuated properly), or if the expansion valve is permanently closed or does not open sufficiently, the air conditioner compressor is also actuated to maximum output (the required temperatures in the battery cooling module are not reached). The pressure on the low-pressure side then only drops to or below the specified value if no cooling output is requested in the air conditioning unit at the same time (-N516- is actuated and closed). The air conditioner compressor draws off the refrigerant from the low-pressure end of both evaporators). However, as no refrigerant can flow via the expansion valve in the air conditioning unit (-N516-) and the cooling output is not reached in the battery cooling module (fault in area of battery cooling module), the electric air conditioner compressor is actuated at a higher speed. As however no more refrigerant can flow, the pressure on the low-pressure end drops below the specified value and the high pressure may also not increase or only increase slightly due to the absence of energy conversion → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner and battery regulation and → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual). |
t | As the output of the evaporator in the battery cooling module is considerably less than that of the evaporator in the air conditioning unit, the specified temperature required may still be attained in the battery cooling module with insufficient refrigerant in the circuit, however the specified temperature will no longer be attained in the evaporator in the air conditioning unit (although the air conditioner compressor is being actuated at a higher speed). |
t | If there is too much refrigeration oil in the circuit, also drain (flush) the air conditioner compressor and renew the receiver/dryer cartridge. After cleaning the refrigerant circuit (flushing with refrigerant R134a → Chapter or blowing out with compressed air and nitrogen → Chapter), add the correct amount of refrigeration oil to the circuit (to the air conditioner compressor) → Chapter. |
Possible deviation from specification | Possible causes of fault | Fault elimination | ||||||||||||||||
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t | It is not initially necessary to clean the refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter) when this problem occurs. Normally, there is only a small quantity of moisture in the system which can be removed by lengthy evacuation. |
t | If a problem involving moisture in the refrigerant circuit only occurs after a lengthy operating period or only infrequently (low pressure drops below specification and evaporator ices up), it is sufficient to renew the dryer in the receiver (adjust quantity of refrigeration oil). Subsequently, evacuate refrigerant circuit for at least 3 hours. |
t | With this fault, the evaporator may ice up although the quantity of refrigerant in the circuit is OK. |
t | A fault at the evaporator output temperature sender -G263- or / and if fitted at the temperature sensor downstream of evaporator for hybrid battery -G757- may also cause the refrigerant circuit to ice up. If this problem occurs, also heed the measured value for -G263- and -G757- (on vehicles with a battery cooling module) → Vehicle diagnostic tester and → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual). |
Possible deviation from specification | Possible causes of fault | Fault elimination | ||||||||||||||||||||||||||||
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t | Observe the following regarding fault „High pressure normal, low pressure too low“: This fault may cause the evaporator to ice up although the amount of refrigerant in the circuit is OK. |
t | If the problem is with the air conditioner compressor (the air conditioner compressor is actuated at excessively high speed by the air conditioner compressor regulating valve -J842-), the refrigerant circuit does not have to be cleaned (flushed with refrigerant R134a → Chapter or blown out with compressed air and nitrogen → Chapter). It is sufficient in this case to renew the air conditioner compressor (heed quantity of refrigerant oil in air conditioner compressor). |
t | If the expansion valve (or one of the two expansion valves) is defective (permanently closed or does not open sufficiently), the air conditioner compressor is also actuated to maximum output and the pressure on the low-pressure end drops to the value in the graph or below (the air conditioner compressor draws off refrigerant from the low-pressure end). As refrigerant cannot however flow via the defective expansion valve, the cooling output is not attained in the downstream evaporator and the high pressure may either not increase or only increase slightly due to the absence of energy conversion. The air conditioner compressor may however be actuated at higher speed, as the required cooling output is not being attained in one evaporator. The same also applies if operation or actuation of the shut-off valve 1 for refrigerant of hybrid battery -N516- or shut-off valve 2 for refrigerant of hybrid battery -N517- is not OK → Vehicle diagnostic tester and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual). |
t | Check the measured values for the evaporator output temperature sender -G263- (and if applicable the measured values for the temperature sensor upstream of evaporator for hybrid battery -G756- and the temperature sensor downstream of evaporator for hybrid battery -G757-) as well as actuation of the air conditioner compressor by the control unit for air conditioning compressor -J842-. If the measured value of -G263- (or -G756-, -G757-) or actuation of the air conditioner compressor is not OK, the evaporator may ice up or the required cooling output is not attained → Vehicle diagnostic tester and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual). |
Possible deviation from specification | Possible causes of fault | Fault elimination | ||||||||||||||||||||||||||||||||||||
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t | This fault may also be caused by too much refrigerant oil in the circuit. Overfilling with refrigerant oil may occur if, for example, the air conditioner compressor has been renewed without adjusting the quantity of refrigerant oil. |
t | If the expansion valve for the evaporator in the air conditioning unit (or for the evaporator in the battery cooling module) is defective (permanently closed or does not open sufficiently), the air conditioner compressor is actuated to maximum output and the low pressure drops to the specified value or below (the air conditioner compressor draws off refrigerant from the low-pressure end). As refrigerant cannot however flow via the expansion valve, the cooling output is not attained and the high pressure may also either not increase or only increase slightly due to the absence of energy conversion. The same also applies if operation or actuation of the shut-off valve 1 for refrigerant of hybrid battery -N516- or shut-off valve 2 for refrigerant of hybrid battery -N517- is not OK → Vehicle diagnostic tester and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual). |
Possible deviation from specification | Possible causes of fault | Fault elimination | ||||||||||||||||||
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t | Overfilling with refrigerant oil may occur if, for example, the air conditioner compressor has been renewed without adjusting the quantity of refrigerant oil. |
t | If for example the expansion valve is defective (permanently open), the evaporator temperature (in the air conditioning unit) is no longer regulated such that only refrigerant in gas form exits from the evaporator. Under certain usage conditions, liquid droplets may then be drawn in by the air conditioner compressor and cause noise (liquid cannot be compressed). |
t | If there is too much refrigerant oil in the circuit, drain the air conditioner compressor and renew the receiver. After cleaning the refrigerant circuit (flushing with refrigerant R134a → Chapter), add the correct amount of refrigeration oil to the circuit → Chapter. |