| Checking heat output and actuation of temperature flaps (air conditioner of „Deluxe“ type) |
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| Close the doors, windows, sun roof and rear lid. |
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| Open all dash panel vents. |
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| Switch on the ignition and activate READY, the engine starts automatically if required (on vehicles with a high-voltage system). |
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| Start the engine (not on vehicles with a high-voltage system). |
| Make the following settings on the air conditioner operating and display unit, Climatronic control unit -J255-: |
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| „Auto“ mode for driver and front passenger side (lamp in AUTO buttons lights) |
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| „Cold“ temperature setting for driver and front passenger side (display „LO“ on display of -J255- and Multi Media Interface) |
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| Air conditioner compressor switched on (lamp in AC button lights). |
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| „Maximum speed“ pre-selected for fresh air blower (-J255- and Mullti Media Interface display speed „10“ or higher) |
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| Use the rotary controls to set the air outflow direction at the air conditioner operating and display unit for the driver and front passenger side to „footwell“ and „dash panel vents“ (indicated on display of -J255- and Multi Media Interface). |
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| The lamps in both AUTO buttons go out when the air outflow direction and/or the fresh air blower speed is/are altered manually. |
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| The maximum possible fresh air blower speed depends on various ambient influences (coolant temperature, vehicle electrical system voltage etc.). |
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| Pressing and holding the rotary control for the driver side temperature setting causes the driver side settings to be adopted for the front passenger side. |
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| Set the potentiometer for rear temperature selection -G538- to „cold“ (installed in vent of rear centre console). |
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| Open the rear centre console vent. |
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| Allow the air conditioner to run for several minutes at maximum cooling output (air conditioner compressor switched on, lamp in AC button lights). |
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| Compare the measured value for the evaporator output temperature sender -G263- to those for the front left chest vent temperature sensor -G385-, the front right chest vent temperature sensor -G386-, the left footwell vent temperature sender -G261- and the right footwell vent temperature sender -G262-. |
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| After 5 minutes, the measured values for the temperature sensors downstream of the heat exchanger (-G385-, -G386-, -G261- and -G262-) must not be more than 5 °C higher than the value for -G263-. |
| If the required values are not obtained, perform the measures to be taken in the event of an increase in temperature downstream of the evaporator → Anchor. |
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| Use a commercially available thermometer to measure the temperature of the air emerging from the rear centre console vents and the rear footwell vents (on the left and right beneath the front seats) and compare the measured values to the temperatures displayed in the measured value block. |
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| The measured values must not be more than 5 °C higher than the temperature sensor measured values displayed. |
| If the required values are not obtained, perform the measures to be taken in the event of an increase in temperature downstream of the evaporator → Anchor. |
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| Use the rotary control on the air conditioner operating and display unit, Climatronic control unit -J255- to select the „warm“ temperature setting for the front passenger side (display „Hi“ on display of -J255- and Multi Media Interface). |
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| Read off the measured values displayed in the measured value block for the temperature sensors (-G263-, -G385-, -G386-, -G261- and -G262-). |
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| Use a commercially available thermometer to measure the temperature of the air emerging from the rear centre console vents (on the left and right). |
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| At -G386- and -G262- the temperature increases to in excess of 52 °C (depending on the instantaneous engine temperature). |
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| At -G385- and -G261- the temperature increases by less than 10 °C as compared to the measured value for -G263-. |
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| The increase in the temperature measured at the vents in the rear centre console is less than 20 °C. |
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| Depending on the engine (e.g. 8-cyl. engine), it may be necessary to increase the engine speed to between 1200 and 1500 rpm to attain the required temperature. At idle, the heat output of the engine or the volume of coolant conveyed through the heat exchanger is not sufficient with all engines to supply the heat exchanger with the heat energy required (e.g. on an 8-cyl.. engine with an idling speed of approx. 650 rpm). |
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| The temperature flaps for the rear vents are actuated (by the rear temperature flap control motor -V137-) by way of a characteristic curve stored in the air conditioner operating and display unit, Climatronic control unit -J255-. If there is a considerable difference between the settings for the left and right side in -J255- and / or the setting at the potentiometer for rear temperature selection -G538-, the temperature flaps for the rear vents are no longer moved to the end stops. The temperature flaps for the temperature of the air from the rear vents are then only actuated such that this air tends to be slightly warmer or colder than for the front vents depending on the setting on -G538-. |
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| On vehicles with a high-voltage system, reduce the speed of the fresh air blower -V2- if applicable. With the engine stopped and maximum fresh air blower speed set, the delivery of the coolant circulation pump -V50- may not always be sufficient to attain the required heat output. |
| Check the following if the readout does not match the specifications: |
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| Repeat the heat output test at an engine speed of approx. 1500 to 2000 rpm (with a lower fresh air blower speed on vehicles with a high-voltage system). If the required heat output is attained at this engine speed (fresh air blower speed), the fault is not in the air conditioning unit, but rather in the coolant circuit (incorporation of air conditioner into coolant circuit, engine coolant pump delivery, flow of coolant through heat exchanger in air conditioning unit etc. → Chapter and → Engine, mechanics; Rep. gr.19). |
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| Foam seal at heat exchanger for heater of air conditioning unit → Chapter |
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| Foam seal at supplementary air heater element -Z35- / at honeycomb element → Chapter |
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| Partitions in air distribution housing between left and right side and between rear and front → Chapter |
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| Proper operation of the engine coolant pump (if the coolant pump is defective, the amount of coolant flowing through the heating system heat exchanger in the air conditioning unit may not be sufficient) → Engine, mechanics; Rep. gr.19 |
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| The coolant circulation pump -V50- is not fitted on all vehicles (depending on model, engine and production period). On vehicles fitted with the optional extra, the circulation pump -V55- assumes the function of -V50-. The circulation pump -V55- is also actuated, depending on the vehicle model and the adaption of the supplementary heater control unit -J364-, by -J364- in response to a request from the air conditioner operating and display unit, Climatronic control unit -J255- at low engine speed to assist the engine coolant pump → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051. |
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| On vehicles with a start-stop system and vehicles with a high-voltage system, the flow of coolant through the heating system heat exchanger in the air conditioning unit is maintained with the engine stopped by the coolant circulation pump -V50-. |
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| Use the rotary control on the air conditioner operating and display unit, Climatronic control unit -J255- to select the „warm“ temperature setting for the driver side (display „Hi“ for driver and front passenger side on display of -J255- and Multi Media Interface). |
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| Read off the measured values for the temperature sensors downstream of the heat exchanger (-G385-, -G386-, -G261- and -G262-). |
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| Use a commercially available thermometer to measure the temperature of the air emerging from the rear centre console vents (on the left and right). |
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| At -G385- and -G261- the temperature increases within 5 minutes to in excess of 52 °C (depending on the instantaneous engine temperature). |
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| The temperatures displayed in the measured value block for the temperature sensors (-G385-, -G386-, -G261- and -G262-) settle to around the same level within 5 minutes (temperature difference less than 5 °C, temperature greater than 52 °C in each case). |
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| The temperature measured at the vents in the rear left and right centre console increases, but does not reach the temperatures indicated for the temperature sensors (-G385-, -G386-, -G261- and -G262-) (the temperature tends to be cooler on account of the setting at the potentiometer for rear temperature selection -G538-) → Anchor. |
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| Depending on the engine (e.g. 8-cyl. engine), it may be necessary to increase the engine speed to between 1200 and 1500 rpm to attain the required temperature. At idle, the heat output of the engine or the volume of coolant conveyed through the heat exchanger is not sufficient with all engines to supply the heat exchanger with the heat energy required (e.g. on an 8-cyl.. engine with an idling speed of approx. 650 rpm). |
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| In the „warm“ temperature setting for the driver and front passenger side, the specified outflow temperature at the evaporator is regulated by the air conditioner operating and display unit, Climatronic control unit -J255- to approx. 10 °C. |
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| On vehicles with a high-voltage system, reduce the speed of the fresh air blower -V2- if applicable. With the engine stopped and maximum fresh air blower speed set, the delivery of the coolant circulation pump -V50- may not always be sufficient to attain the required heat output. |
| Check the following if the readout does not match the specifications → Anchor. |
| Continue as follows if the readout matches the specifications: |
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| Set the potentiometer for rear temperature selection -G538- to „warm“ (installed in vent of rear centre console). |
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| Use a commercially available thermometer to measure the temperature of the air emerging from the rear centre console vents and the rear footwell vents (on the left and right) and compare to the measured values displayed for the temperature sensors (-G385-, -G386-, -G261- and -G262-). |
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| The measured temperature of the air emerging from the vents in the rear centre console and the rear footwell vents (on the left and right) increases and, within 5 minutes, attains a value which is less than 10 °C below the lowest value measured by the temperature sensors and displayed. |
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| The difference between the temperature measured on the left and right side is less than 5 °C. |
| Check the following if the readout does not match the specifications: |
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| Further checks if the readings do not match the specifications → Anchor. |
| Continue as follows if the readout matches the specifications: |
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| Use the rotary control on the air conditioner operating and display unit, Climatronic control unit -J255- to select the „cold“ temperature setting for the front passenger side (display „Lo“ on display of -J255- and Multi Media Interface). |
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| Compare the measured value displayed for the evaporator output temperature sender -G263- to those for -G386- and -G262- and read off the measured values for -G385- and -G261-. |
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| At -G385- and -G261- there is only a slight change in the temperatures measured and displayed and these remain in excess of 52 °C (depending on the instantaneous engine temperature). |
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| At -G386- and -G262- the temperature decreases and, after 5 minutes at the latest, reaches a value not more than 10 °C higher than the values for the evaporator output temperature sender -G263-. |
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| Depending on the engine (e.g. 8-cyl. engine), it may be necessary to increase the engine speed to between 1200 and 1500 rpm to attain the required temperature. At idle, the heat output of the engine or the volume of coolant conveyed through the heat exchanger is not sufficient with all engines to supply the heat exchanger with the heat energy required (e.g. on an 8-cyl.. engine with an idling speed of approx. 650 rpm). |
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| In the „warm“ temperature setting for the driver and front passenger side, the specified outflow temperature at the evaporator is regulated by the air conditioner operating and display unit, Climatronic control unit -J255- to approx. 10 °C. If the „cold“ temperature setting is selected for one side, the air conditioner operating and display unit, Climatronic control unit -J255- reduces the specified outflow temperature at the evaporator and this is regulated to approx. 2 °C. |
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| On vehicles with a high-voltage system, reduce the speed of the fresh air blower -V2- if applicable. With the engine stopped and maximum fresh air blower speed set, the delivery of the coolant circulation pump -V50- may not always be sufficient to attain the required heat output. |
| Check the following if the readout does not match the specifications → Anchor. |
| Testing is over if the readout matches the specifications. |
| Measures to be taken in the event of temperature increase downstream of evaporator |
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