Cooling Output, Checking
Cooling Output, Checking
• The requirements for testing the cooling capacity are fulfilled. Refer to => [ A/C Cooling Output, Testing Requirements ] A/C Cooling Output, Testing Requirements.
- Measure the ambient temperature (must be warmer than 15 °C (59 °F)).
- Close the doors, the engine hood, the windows, the sunroof and the rear lid.
- Open all instrument panel vents and the vent in the rear center console.
- In the case of a Comfort A/C system, open the vents in the B-pillar.
- Start the engine.
- Switch off the A/C compressor (set "Econ" mode on the Climatronic control module (J255) ; the indicator lamp in the AC button does not illuminate).
- Start Guided Fault Finding of the A/C system (on the Climatronic control module (J255) ) using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- Select the measured values for the activation of the A/C compressor and the pressure in the refrigerant circuit and read out the measured values in the "Read measured values" function using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• For the following test, various measured values can be selected and displayed in a table using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
When testing the cooling output, it is helpful to display the following measured values of the Climatronic control module:
• The measured values of the following temperature sensor ( left vent temperature sensor (G150) , right vent temperature sensor (G151) , Left footwell vent temperature sensor (G261) , right footwell vent temperature sensor (G262) , evaporator vent temperature sensor (G263) ).
• Activation of the following components fresh air blower (V2) , coolant fan (V7) , coolant fan 2 (V177).
• The activation of the following components (if present, depending on the equipment and engine type coolant pump (V50) / recirculation pump (V55) , coolant shut-off valve (N82) / heater coolant shut-off valve (N279) )
• The activation of the A/C compressor regulator valve (N280) (compressor shut-off conditions and actual compressor current).
• The coolant temperature and the ambient temperature.
• The measured value of the A/C pressure/temperature sensor (G395) (coolant pressure).
Checking
• The A/C compressor is switched off. A current of 0 A (amps) for the activation of the A/C compressor regulator valve is displayed.
• The pressure in the refrigerant circuit is same as the measured outside temperature or greater than the value in the chart.
• At absolute pressure, 0 bar corresponds to absolute vacuum. Normal ambient pressure equals approximately 1 bar absolute pressure and 0 bar pressure. On the scales of most pressure gauges, 0 bar pressure corresponds to an absolute pressure of one bar (can be seen from -1 mark below 0).
• Depending on the version of the Climatronic control module, only integer values may be displayed as measured values. If the measured pressure is between two values, the display alternates between the two values.
• Pressure in refrigerant circuit is governed by ambient temperature. On account of heat given off by components (for example, the radiator), pressure displayed with warm engine will be slightly higher than that given for the respective ambient temperature.
• If pressure displayed is below that indicated in table. Check the signal of the A/C pressure/temperature sensor (G395) using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function. If no fault is determined at the A/C pressure/temperature sensor, there is insufficient coolant in the circuit. Bring vehicle to a workshop that has the necessary tools and in which the work can be performed accordingly by qualified personnel.
Refrigerant circuit pressure OK
- Switch the A/C compressor on by selecting the "Auto" mode on the Climatronic control module (and on the rear A/C display control head if present) (the indicator lamps in the AUTO buttons and the AC button illuminate).
• By pressing the SYNC button on the Climatronic control module (only in the Comfort version), the settings for the front driver side are applied to the front passenger side and also on the rear A/C display control head if present.
- Via the rotary switches of the Climatronic control module, the temperature preselection is set to "cold" (for the driver and front passenger side).
- In vehicles with a rear A/C display control head (E265) , also set the temperature preselection for the rear to "cold" (for the left and right side).
- Via the rotary switches on the Climatronic control module, set the air flow direction to the instrument panel vents (for the driver and front passenger side).
- In vehicles with a rear A/C display control head, set the air flow direction via the rotary switches on the rear A/C display control head to the vents in the rear center console.
• The indicator lamp in the AUTO buttons goes out when the vent direction for the air and/or fresh air blower speed is manually changed.
• The maximum possible fresh air blower speed depends on several environmental conditions (on-board voltage, etc.).
- In the "Read measured values" function, read out the actual current with which the A/C compressor regulator valve (N280) is activated (if the actual current is greater than 0.3 A, the A/C compressor is switched on) using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The target current for activating the A/C compressor regulator valve is calculated by the Climatronic control module. The request is sent via the data bus to the vehicle electrical system control module (J519) and the vehicle electrical system control module activates the A/C compressor regulator valve and reports the actual current. Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• If no or very little current is displayed as the measured value, check the activation of the A/C compressor regulator valve. Refer to => [ A/C Compressor Regulator Valve (N280), Checking Switch-On Signal ] A/C Compressor Regulator Valve (N280), Checking Switch-On Signal.
• The A/C compressor regulator valve is activated by the Climatronic control module via the vehicle electrical system control module. The activation of the A/C compressor regulator valve is displayed as the measured value in the vehicle electrical system control module. Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The actual current flowing through the A/C compressor regulator valve is measured by the vehicle electrical system control module and is sent via the data bus to the Climatronic control module. Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- In the "Read measured values" function, read out the pressure in the refrigerant circuit measured by the A/C pressure/temperature sensor (G395). The displayed pressure increases above the value when the A/C compressor is switched off. Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The pressure displayed in the displayed measured value does not change and the A/C compressor activation is OK. Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function. Check again whether the A/C compressor is actually driven and the A/C compressor regulator valve (N280) is activated. If the A/C compressor is being driven and the A/C compressor regulator valve is activated, there is a malfunction in the refrigerant circuit. Bring vehicle to a workshop that has the necessary tools and in which the work can be performed accordingly by qualified personnel. (it is possible that A/C compressor regulation is not OK). Bring the problems determined to the attention of the workshop.
• The A/C compressor regulator valve is activated by the Climatronic control module (via the vehicle electrical system control module) so that the temperature of the air downstream from the evaporator reaches the specified value (approximately 2-5° C (35 - 41 °F)).
• After vehicle start, a value greater than 0.55 A is displayed for the activation of the A/C compressor regulator valve depending on the measured temperature, the engine speed and the vehicle voltage. As soon as the temperature measured by evaporator vent temperature sensor (G263) nears the specified value, the activation, and thus the compressor output, is reduced.
• Under certain operating conditions, moisture in the refrigerant circuit can lead to ice build-up on the A/C compressor regulator valve (and on the expansion valve). A/C compressor control is reduced by this ice build-up, evaporator is cooled too intensely and freezes. The ice on the evaporator may cause various customer concerns. Refer to => [ Ice Formation on Evaporator, Localizing Malfunction ] Ice Formation on Evaporator, Localizing Malfunction.
- Press the button for recirculation mode on the Climatronic control module (J255) (symbol for recirculation mode in the Umluft button illuminates).
- Set engine speed of 2000 rpm (start of time measurement).
- In the "Read measured values" function, read out the measured value of the evaporator vent temperature sensor (G263) using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- Use a thermometer to measure the temperature of the air from the vent in the rear center console.
- Compare the displayed value (from the evaporator vent temperature sensor evaporator vent temperature sensor) with the values in the diagram.
A Air temperature measured by the evaporator vent temperature sensor (after evaporator in the rear A/C unit)
B Ambient temperature
C Permissible tolerance range
• Depending on the ambient temperature, the measured air temperature after the evaporator (measured value of the evaporator vent temperature sensor) must be within the stated tolerance range - C - after 5 minutes.
• The measured temperatures from the vents of the rear center console correspond to the temperature measured by the evaporator vent temperature sensor. Permissible deviation from the measured value of the front evaporator vent temperature sensor maximum + 9° C (48 °F) (but not lower than +1° C (34 °F)).
• If the required values for the front are not reached, check the measured value of the evaporator vent temperature sensor. Compare the displayed measured value of the evaporator vent temperature sensor to the measured values of the left vent temperature sensor (G150) and the right vent temperature sensor (G151).
• The measured value from the evaporator vent temperature sensor evaporator vent temperature sensor only slightly deviated from the measured value form the center outlet temperature sensor left vent temperature sensor / right vent temperature sensor. Perform "Identifying malfunctions if specified values are not obtained". Refer to => [ Malfunction Determination in Case of Deviation from Target Value (Required Cooling Output Of A/C System Is Not Achieved) ] Malfunction Determination In Case of Deviation From Target Value (Required Cooling Output of A/C System Is Not Achieved).
• If the measured value of the evaporator vent temperature sensor is greater than the measured value of the left vent temperature sensor or the right vent temperature sensor, check the evaporator vent temperature sensor for proper installation. Refer to => [ Evaporator Vent Temperature Sensor (G263) ] Evaporator Vent Temperature Sensor (G263) and perform an electrical test for this sensor using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• If the measured temperatures from the rear center console vents are more than 1° C (34 °F) less than the measured value of the evaporator vent temperature sensor, check the temperature sensors responsible for the measurement (due to the design of the A/C system, the rear temperature cannot be less than the front temperature).
• The function of the A/C unit is, for example recognizable, when the refrigerant line on the low pressure side (wide line between the inner heat exchanger and the A/C compressor) cools down and the refrigerant line on the high pressure side (narrow line between the condenser and inner heat exchanger) warms up. Refer to => [ Refrigerant Circuit Components Overview ] Refrigerant Circuit Components Overview.
If the measured value of the evaporator vent temperature sensor (G263) (and thus the cooling output of the A/C system) and the measured temperature of the air from the rear center console vents are OK and if there is no problem, the cooling output test ends.
• If the measured value of the evaporator vent temperature sensor (and thus the cooling output of the A/C system) is not OK, determine the malfunction causing the deviation from the target value (the required cooling output is not reached). Refer to => [ Malfunction Determination in Case of Deviation from Target Value (Required Cooling Output Of A/C System Is Not Achieved) ] Malfunction Determination In Case of Deviation From Target Value (Required Cooling Output of A/C System Is Not Achieved).
• If the measured value of the evaporator vent temperature sensor (and thus the cooling output of the A/C system) is OK and if there is a complaint that the A/C system vent temperatures are too high or differ, check the activation of the temperature doors in the A/C system. Refer to => [ Heat Output and Temperature Door Activation, Checking ] Heat Output and Temperature Door Activation, Checking and the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• If the measured value of the evaporator vent temperature sensor (and thus the cooling output of the A/C system) is OK and there is a problem due to a lack of cooling output from the rear vents (the rear vent temperatures are too high or differ), check the activation of the temperature doors in the rear vent air guide: Basic version, refer to => [ Malfunction Determination - Cooling Output of Front A/C System OK but Required Values Not Achieved In Rear - Basic System ] Malfunction Determination - Cooling Output of Front A/C System OK But Required Values Not Achieved In Rear - Basic System, Comfort version, refer to => [ Malfunction Determination - Cooling Output of Front A/C System OK but Required Values Not Achieved In Rear - Comfort System ] Malfunction Determination - Cooling Output of Front A/C System OK But Required Values Not Achieved In Rear - Comfort System and the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.