Cooling Output, Checking
Cooling Output, Checking
Not for vehicles with a high voltage system (hybrid vehicles)
Only on vehicles with mechanically driven A/C compressors
• 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.
- Start the engine.
- Switch off the A/C compressor (set the "Econ" mode on the Climatronic control module (J255) A/C display control head. The indicator lamp in the AC button does not illuminate).
- Perform a Guided Fault Finding on the A/C system using the Vehicle diagnostic tester in "Guided Fault Finding".
- In "read measured values block" select the display group with the measured values for the compressor control and refrigerant circuit pressure and read the measured values using the Vehicle diagnostic tester in "Guided Fault Finding" function.
• The A/C compressor is switched off, a current of 0 A (amps) will be 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 (14.5 psi) 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 version of the Climatronic control module (J255) , only integer values may be displayed in the measured values block, if the pressure measured lies between two values the display switches back and forth.
• Pressure in refrigerant circuit is governed by ambient temperature. On account of heat given off by components (e.g. 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 coming from the A/C pressure/temperature sensor (G395) using the Vehicle diagnostic tester in "Guided Fault Finding". 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 (the indicator lamps in the AUTO buttons and the AC button illuminate).
- Using the dial on the Climatronic control module, set the temperature preselect to "cold" (for the driver and passenger side).
- On vehicles with the "Comfort" A/C system, set the rear temperature selection potentiometer (G538) to "cold" (installed in the rear center console vent).
- Using the rotary switch on the Climatronic control module set the vent direction to "instrument panel vents" (for the driver's and passenger's side).
• The indicator lamp in the one or both AUTO buttons goes out when the vent direction for the air or fresh air blower speed is manually changed.
• The maximum possible fresh air blower speed depends on several conditions (coolant temperature, vehicle voltage, etc.)
- In the "read measured values block", read the specified current which is controlled by the A/C compressor regulator valve (N280) (if the specified current is greater than 0.3 A, then the A/C compressor should be switched on) using the Vehicle diagnostic tester in "Guided Fault Finding".
• The current is calculated by the Climatronic control module, the request is sent via the Data bus on the Vehicle Electrical System Control Module (J519). Check using the Vehicle diagnostic tester in "Guided Fault Finding".
- In "read measured values block" read the actual current which is controlled by the A/C compressor regulator valve (if the actual current is greater than 0.3 A, then the compressor is switched on) using the Vehicle diagnostic tester in "Guided Fault Finding".
• If no or very little current is displayed in measured values block, check actuation of 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 Climatronic control module actuates the A/C compressor regulator valve via the vehicle electrical system control module. The actuation of the A/C compressor regulator valve is displayed in the vehicle electrical system control module measured values block using the Vehicle diagnostic tester in "Guided Fault Finding".
• The actual current, which flows through the A/C compressor regulator valve is measured by the vehicle electrical system control module and sent by the Climatronic control module. Check using the Vehicle diagnostic tester in "Guided Fault Finding".
- In "read measured values block" read the refrigerant circuit pressure 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 "Guided Fault Finding".
• If the pressure displayed in the measured values block does not change, then the A/C compressor actuation is OK. Check using the Vehicle diagnostic tester in "Guided Fault Finding". Check again if the compressor is really driven if the A/C compressor regulator valve (N280) is being actuated; if the A/C compressor is driven and A/C compressor regulator valve is actuated, then 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.
• A/C compressor regulator valve is activated by the Climatronic control module (via the A/C compressor regulator valve ) so that temperature of air downstream of evaporator reaches the specified value (approximately 2 to 5 °C (35 to 41 °F):
• A value greater than 0.55A is displayed after vehicle start, depending on temperature, engine speed and vehicle voltage measured. As soon as the temperature measured by the evaporator vent temperature sensor (G263) nears the target value, the activation, and thus the compressor output, is reduced.
• Under certain operating conditions, residual moisture in the refrigerant circuit can lead to an ice build-up at the A/C Compressor Regulator Valve (and at 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, (the symbol for "recirculation mode" in the air recirculation button illuminates).
- Set engine speed of 2000 rpm (start of time measurement).
- In "read measured values block" read the measured values for the evaporator vent temperature sensor (G263) using the Vehicle diagnostic tester in "Guided Fault Finding".
- Compare the displayed value (from the evaporator vent temperature sensor) with the values in the diagram.
A Measured air temperature of Evaporator Vent Temperature Sensor (after evaporator)
B Ambient temperature
C Permissible tolerance range
Depending on ambient temperature, air temperature measured must be within stated tolerance range - C - after 5 minutes.
• If the required values are not reached, check the measuring value for the Evaporator Vent Temperature Sensor. Compare the displayed values from the evaporator vent temperature sensor with the measured values from the center outlet temperature sensor (G191) (on the "Basis" ) / with the Left Front Upper Body Outlet Temperature Sensor (G385) (on the "Comfort").
• The measured value from the evaporator vent temperature sensor only slightly deviated from the measured value from the center outlet temperature sensor / Left front upper body vent temperature sensor. Perform -Identifying malfunctions if specified values are not obtained-. Refer to => [ Required Cooling Output Not Reach, Malfunction Notification ] Required Cooling Output Not Reach, Malfunction Notification.
• If the measured value of the evaporator vent temperature sensor is greater than the measured value of the center outlet temperature sensor or of the left front upper body outlet temperature sensor, then make sure the is installed correctly. Refer to => [ Evaporator Vent Temperature Sensor (G263) ] Evaporator Vent Temperature Sensor (G263) and perform an electrical test on this sensor using the Vehicle diagnostic tester in "Guided Fault Finding".
• The function of the A/C unit is, for example recognizable, when the refrigerant line "low pressure side" (wide line between the quick acting coupling and the compressor) cools down and the refrigerant line "high pressure side" (narrow line between the condenser and quick acting coupling) warms up. Refer to => [ Refrigerant Circuit Component Overview ] Refrigerant Circuit Component Overview.
If the Evaporator Vent Temperature Sensor (G263) measured value (and with it the cooling performance of the A/C ) is OK, and if there is no complaint, then the cooling capacity test is completed
• If the evaporator vent temperature sensor measured value (and with it the A/C cooling output) is not OK, then determine the malfunction causing the difference from the specified value (the required A/C cooling output is not reached). Refer to => [ Required Cooling Output Not Reach, Malfunction Notification ] Required Cooling Output Not Reach, Malfunction Notification.
• If the evaporator vent temperature sensor. measured value (and with it the A/C cooling output) is OK, and if there is still a complaint that the vent temperatures are too high or differ, check the actuation of the temperature doors. Refer to Basis => [ Heating Output and Temperature Door Activation, Checking, Basis ] Heating Output and Temperature Door Activation, Checking, Basis or Comfort => [ Heat Output and Temperature Door Activation, Checking, Comfort ] Heat Output and Temperature Door Activation, Checking, Comfort.