Cooling Output, Checking
Cooling Output, Checking
Special tools, testers and auxiliary items required
• Vehicle diagnosis, testing and information system (VAS5051B) (or Vehicle Diagnosis and Service System (VAS 5052) ).
• A standard thermometer (for temperature measurements, if necessary a thermometer with 2 measuring probes for simultaneous measurement e.g. for temperature on the right and left)
Test requirements are met, refer to => [ Test Requirements ] Test Requirements.
- Measure the ambient temperature (it must higher than 15 °C).
- Close doors, hood, windows and sun roof.
- Open all instrument panel vents.
- Switch ignition on.
- Start the engine.
- Switch on "Econ" on the Climatronic control module (J255) (the indicator lamp in the ECON button will come on; the indicator lamp in the AC button will not come on).
- Initiate a Guided Fault Finding on the A/C system using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
- 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 on the Vehicle diagnosis, testing and information system (VAS5051B) 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.
• In terms of absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure equals approximately 1 bar absolute pressure. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of one bar (can be seen from -1 mark below 0).
• Depending on version of Climatronic Control Module (J255) , only integer values may be displayed in the measuring value 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 the displayed pressure in the refrigerant circuit is lower than in the table
• Check signal of High Pressure Sensor (G65). Refer to=> [ High Pressure Sensor (G65), Checking Pressure Signal ] Testing and Inspection.
• If no malfunction can be detected at High Pressure Sensor (G65) , there is insufficient refrigerant 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.
If pressure in refrigerant circuit is OK (the same or greater than specified in the table)
- Switch on A/C compressor, select operating mode "Auto" on Climatronic Control Module (J255) to do so.
- Set temperature preselect for driver and front passenger side to "Lo" on Climatronic Control Module.
- Set direction of air flow to "instrument panel vents" at the Climatronic Control Module.
- Read the required values in Guided Fault Finding using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
Check the following values:
• The A/C compressor is switched on; a duty cycle greater than 30% is displayed (the A/C compressor regulator valve (N280) is activated).
• The A/C compressor is switched on, the current greater then 0.3 A is displayed (the current flows via the A/C compressor regulator valve).
• The displayed pressure increases above the value when the compressor is switched off.
• If the measured pressure does not change and the A/C compressor activation is OK, then check one more time if the A/C compressor is actually being driven. If the A/C compressor is being driven, 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.
• A/C Compressor Regulator Valve (N280) is activated by the Climatronic Control Module (J255) so that temperature of air downstream of evaporator reaches the specified value (approximately 2 to 5 °C):
• A value greater than 75% (0.55 A) is displayed after vehicle start, depending on measured temperature, engine speed and vehicle voltage for activation of A/C compressor regulator valve. 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, 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.
• If no voltage or voltage that is too low is shown in the measured values block for the A/C compressor regulator valve activation, check the A/C compressor regulator valve activation. Refer to => [ A/C Compressor Regulator Valve (N280), Checking Switch-On Signal ] A/C Compressor Regulator Valve (N280), Checking Switch-On Signal.
- Press button for recirculating air mode on Climatronic Control Module (J255) (symbol for "recirculating air mode" lights up in button).
- Set engine speed of 2000 rpm (start of time measurement).
- In "read measured values block", select the display with the measured value from the evaporator vent temperature sensor (G263). Refer to Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
- Compare the displayed measured value (of the evaporator vent temperature sensor ) to the values in the diagram using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
A Measured air temperature of Evaporator Vent Temperature Sensor (G263)
B Ambient temperature
C Permissible tolerance range
Depending on the ambient temperature, the measured air temperature should be after 5 minutes within the shown tolerance range.
• If the required values are not reached, check the measured values on the evaporator vent temperature sensor, on the left vent temperature sensor (G150) and on the right vent temperature sensor (G151) , then compare the displayed measured values with each other:
• If the measured value deviates in the display fields, then perform the procedure for identifying malfunctions if specified values are not reached. Refer to => [ Determining Malfunction if Specified Values Are Not Obtained ] Determining Malfunction if Specified Values Are Not Obtained.
• If measured value of Evaporator Vent Temperature Sensor is greater than measured value of Left Vent Temperature Sensor and Right Vent Temperature Sensor, check Evaporator Vent Temperature Sensor for proper installation and perform an electrical test for this sensor using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
• The function of the air conditioning is recognizable, e.g. the refrigerant pipe on the low pressure side (thick line) cools off.
If the measured value for the evaporator vent temperature sensor (and therefore the system output) is OK:
- Compare the measured value for the Evaporator Vent Temperature Sensor with the measured values for the Left Vent Temperature Sensor and Right Vent Temperature Sensor.
The left vent temperature sensor and right vent temperature sensor measured values may not be greater than maximum 3 °C after 5 minutes, than the evaporator vent temperature sensor measured value.
• If the required values are not reached, then compare the displayed measured values from the left vent temperature sensor and the right vent temperature sensor to each other:
• If the measured value in one of the two sensors is OK, then check the activation and function of the left temperature door motor (V158) and the right temperature door motor (V159). Refer to=> [ Temperature Increase Downstream from Evaporator, Determining Malfunction ] Temperature Increase Downstream From Evaporator, Determining Malfunction, => [ Heating Performance Of A/C System, Checking ] Heating Performance Of A/C System, Checking and Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
• If the measured value from the left vent temperature sensor (G150) and from the right vent temperature sensor (G151) is lower then the value from the evaporator vent temperature sensor (G263) make sure the evaporator vent temperature sensor, left vent temperature sensor and right vent temperature sensor are installed correctly and check their electrical connectors for contact resistance. Replace the faulty sensor if necessary. Refer to Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
• If there is no malfunction on the left vent temperature sensor and the right vent temperature sensor as well as on the left temperature door motor (V158) and the right temperature door motor, then determine the malfunction with temperature increase downstream of the evaporator. Refer to => [ Temperature Increase Downstream from Evaporator, Determining Malfunction ] Temperature Increase Downstream From Evaporator, Determining Malfunction.
• Temperature of air flowing out of center instrument panel vents can also be measured, for example, using a commercially available thermometer.
• If different air temperatures are measured from the vents when the A/C is being used, then this may be caused by the following: the temperature doors in the air distribution housing may not be closing completely or are not in their end position. Refer to => [ Air Guide In Evaporator Housing ] Air Guide In Evaporator Housing and Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function, there may be air in the heater core (the heater core then flows unevenly and at different temperatures). Refer to=> [ Heating Performance Of A/C System, Checking ] Heating Performance Of A/C System, Checking or the foam seal has come loosen when the heater core was installed and air can flow over the heater core.