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 => [ Cooling Performance Test Requirements ] Cooling Performance Test Requirements.
- Measure the ambient temperature (it must higher than 15 °C).
- Close doors, hood, windows and rear lid.
- Open all dash panel vents.
- Switch ignition on.
- Start the engine.
- Switch on "Econ" in the Climatronic control module (J255) (indicator light in AC button does not light up).
- Initiate a Guided Fault Finding on the A/C system using (VAS5051B) under "Guided Fault Finding."
- Select "read measured values block", display group with the measured values for the A/C compressor control and the pressure inside the refrigerant circuit and read the measured values using (VAS5051B) under "Guided Fault Finding."
- Check the displayed measured values in the display fields with the values for the A/C compressor regulator valve (N280) control and the pressure inside the refrigerant circuit:
• The compressor is switched off, a current of 0 A (amps) to the A/C compressor regulator valve (N280) will be displayed.
• The pressure in the refrigerant circuit ( high pressure sensor (G65) measured value) is the same or greater than the valued listed in the table at the measured ambient temperature.
• 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).
• At this time, only integer values are displayed for this vehicle in the measuring value block, if the pressure measured lies 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 (e.g. radiator), pressure displayed with warm engine will be slightly higher than that given for the respective ambient temperature.
• If pressure displayed is lower than specified in the table, check the high pressure sensor signal. Refer to => [ High Pressure Sensor (G65), Checking Pressure Signal ] High Pressure Sensor (G65), Checking Pressure Signal. If there is no fault on the high pressure sensor, then there is not enough 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. Inform the workshop of the fault (insufficient refrigerant in the circuit.
Refrigerant circuit pressure OK
- Switch the A/C compressor on by selecting "Auto" on the Climatronic control module (J255) (indicator lights in AUTO button and AC button light up).
- Turn the Climatronic control module temperature rotary switch to "cold".
- Adjust air output direction via the air distribution rotary switch on the Climatronic control module to "Instrument panel vents".
- In "read measured values" select the display group with the measured values for controlling the A/C compressor regulator valve (N280) and the measured value for the high pressure sensor using (VAS5051B) under "Guided Fault Finding."
- Check display in display zones:
• A duty cycle greater than 30% is displayed (the A/C compressor regulator valve (N280) is controlled, A/C compressor is switched on).
• A current greater than 0.3 A is displayed (current flows via A/C compressor regulator valve, compressor is switched on)
• If no or very little current is displayed in display field, 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 displayed refrigerant circuit pressure increases above the value when the A/C compressor is switched off.
• If the display pressure does not change and the A/C compressor activation is OK, then see if the A/C compressor is actually being driven. If the A/C compressor is being driven, then the fault is 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. Bring the problems determined to the attention of the workshop.
• A/C Compressor Regulator Valve is activated by Climatronic control module so that temperature of air downstream of evaporator reaches the specified value (approximately 2 to 5 °C):
• A value greater than 75% (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, 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 recirculation button on Climatronic control module (symbol for "recirculating air mode" lights up in recirculation 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) using (VAS5051B) under "Guided Fault Finding."
- Compare the displayed evaporator vent temperature sensor value with the values in the diagram.
A Air temperature measured by the evaporator vent temperature sensor
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 necessary values are not reached, check the measured values from the evaporator vent temperature sensor and the measured value from the left front upper body outlet temperature sensor (G385). Compare the displayed measured values with each other:
• The measured value from the evaporator vent temperature sensor differs from the measured value from the left front upper body outlet temperature sensor by just a little. Perform=> [ Determining Malfunction if Specified Values Are Not Obtained ] Determining Malfunction if Specified Values Are Not Obtained.
• If the measured value from the evaporator vent temperature sensor is greater than the measured value from the left front upper body outlet temperature sensor (G385) , then make sure the evaporator vent temperature sensor is installed correctly and perform an electrical test on this sensor using (VAS5051B) under "Guided Fault Finding."
• 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 (G263) (and therefore the system output) is OK:
- Adjust air output direction via the air distribution rotary switch on the Climatronic control module (J255) to "footwell".
- Compare the displayed value from the evaporator vent temperature sensor to the measured values from the left footwell vent temperature sensor (G261) and right footwell vent temperature sensor (G262).
The center outlet temperature sensor and footwell outlet 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, compare the displayed measured values for the left footwell vent temperature sensor and right footwell vent temperature sensor with each other:
• If the measured value from the left footwell vent temperature sensor or the right footwell vent temperature sensor is OK, check the actuation and the 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 (VAS5051B) in "Guided Fault Finding."
• If the measured value from the left footwell vent temperature sensor and/or from the right footwell vent temperature sensor is lower than the measured value from the evaporator vent temperature sensor (G263). Make sure the evaporator vent temperature sensor, left footwell vent temperature sensor and right footwell vent temperature sensor are installed correctly and check their electrical connectors for contact resistance. Replace the faulty sensor if necessary. Refer to (VAS5051B) in "Guided Fault Finding."
• If there is no fault found on the left footwell vent temperature sensor (G261) , right footwell vent temperature sensor (G262) and evaporator vent temperature sensor (G263) as well as on the left temperature door motor (V158) and right temperature door motor (V159) , 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.
• The air temperature flowing out of the "center" instrument panel vents. A commercially available thermometer can also be used.
• If there is a complaint of a different temperature of air from vents in A/C system regulated mode as at the same setting in regulated mode, the causes for this may be temperature doors in the heating and A/C unit is not opening or closing completely, or is not quite reaching its end position). Refer to => [ Air Routing and Distribution in Passenger Compartment ] Air Routing and Distribution in Passenger Compartment and (VAS5051B) in "Guided Fault Finding." There is air in the heater core (fluctuating flow through heater core and heat is not distributed uniformly). Refer to=> [ Heating Performance Of A/C System, Checking ] Heating Performance Of A/C System, Checking. A foam seal has loosened during installation of heater core and air may flow past at heater core. The A/C system refrigerant circuit is not filled with the correct quantity of refrigerant.