A/C Unit, Checking Cooling Output
A/C Unit, Checking Cooling Output
=> [ Determining Malfunction if Specified Values Are Not Obtained ]
=> [ Determining Malfunction if Temperature Increase Downstream from Evaporator ]
Special tools, testers and auxiliary items required
• Vehicle diagnosis, testing and information system (VAS 5051/) or
• Vehicle diagnosis, testing and information system (VAS 5052 A).
• Standard thermometer (for temperature measurements, if necessary a thermometer with 2 measuring probes for simultaneous measurement e.g. for temperature at right and left)
Test Prerequisites
• Ambient temperature greater than 15° C.
• The radiator and condensers are clean. Clean them if necessary.
• The A/C compressor drive unit is installed correctly; the A/C compressor is actually being driven, refer to => [ A/C Compressor Drive Unit ] Description and Operation.
• All air ducts, covers and seal OK and properly installed.
• The air flow through the dust and pollen filter is not affected by dirt in the filter, refer to => [ Dust and Pollen Filter ] Service and Repair.
• The air intake (in fresh air and recirculation modes) is not affected by dirt or retrofitted components.
• The vehicle is not exposed to sunlight.
• The engine is warm.
• The Climatronic Control Module (J255) DTC memory has been checked and erased and basic setting has been performed using Vehicle Diagnosis, Testing and Information System VAS 5051/ under "Guided Fault Finding".
• The Climatronic control module code and adaptation have been checked using Vehicle Diagnosis, Testing and Information System VAS 5051/ under "Guided Fault Finding".
- Switch the ignition on and set the following settings on the Climatronic control module:
• Auto operating mode (indicator light in the AUTO button lights up).
• The temperature knob is in the cold position.
• A/C compressor on (the indicator lamp in the AC button comes on).
- Start the engine and check the following functions:
• The Coolant Fan (V7) and Coolant Fan 2 (V177) run (the activation and speed depend on the pressure in the refrigerant circuit and the engine temperature.
• Depending on the version of the Climatronic control module, the coolant fan and coolant fan 2 are only switched at a certain pressure in the refrigerant circuit (currently from a pressure approximately 9 bar). For checking the radiator fan actuation, refer to vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding".
• Fresh Air Blower (V2) runs at maximum speed.
• The A/C system goes into recirculation mode (approximately 1 minute after starting the vehicle, the back pressure/fresh air doors are closed and the recirculation door is opened, the fresh air blower extracts the air from the passenger compartment below the instrument panel/glove compartment).
• The Coolant Pump (V50) does not run.
• The Left Heat Regulating Valve (N175) and the Right Heat Regulating Valve (N176) are closed, the coolant lines to the heater core and the heat exchanger in the A/C unit cool down.
• Temperature of the air coming out of the heater heat exchanger is displayed in the measured values block (Left Vent Temperature Sensor (G150) and Right Vent Temperature Sensor (G151)measured values). Refer to vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding".
• If the Climatronic control module has been removed from the center console. The electrical connections cannot be separated for this purpose. If the coolant and refrigerant lines can be reached through the installation compartment, and their temperature can be felt with the hand refer to (Climatronic control module, removing => [ Climatronic Control Module ] Climatronic Control Module). To feel if the coolant lines are cooling off, carefully touch them through the installation shaft in the instrument panel (they may still be hot).
• If one of these test conditions is not fulfilled, check the DTC memory, perform the output diagnostic test mode and read the measured values for the Climatronic control module from the vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding".
Checking
- Measure the ambient temperature (it must higher than 15 °C).
- Close the engine hood, the doors and the windows.
- Open all dash panel vents.
- With the ignition switched off, connect the (VAS 5051/) with the (VAS 5051/5A) to the 16-pin Data Link Connector (DLC). Refer to vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding".
- Initiate a Guided Fault Finding on the A/C system using vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding".
- Press the AC button on the Climatronic control module to switch the A/C system off (the indicator lamp in the AC does not come on).
- Select the display group with the following valued in "read measured values block". A/C Compressor Regulator Valve (N280) activation and A/C Pressure/Temperature Sensor (G395) measured values. Checking the display using vehicle diagnosis, testing and information system VAS 5051/ in "Guided Fault Finding" function.
• The A/C compressor is switched off by the A/C compressor regulator valve. The A/C compressor is switched off, 0% appears in the display field.
• The pressure in the refrigerant circuit determined by the A/C pressure/temperature sensor is the same or greater than the value 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. 0 bar pressure corresponds to an absolute pressure of one bar on most pressure gauges (indicated by -1 below 0).
• At this time, only integer values are displayed for the pressure in the refrigerant circuit, 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, for example, the radiator. A higher pressure will be displayed on an engine that is at operating temperature than at ambient temperature.
If Pressure Displayed Is Below That Indicated In Table:
- To check the A/C pressure/temperature sensor signal, read the measured values from the vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding".
- If no malfunction in the signal from the A/C pressure/temperature sensor can be found, there is not enough 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 system on at the Climatronic control module as follows:
• The engine is running.
• Auto operating mode (indicator light in the AUTO button lights up).
• The temperature knob is in the cold position.
• Air distribution knob to instrument panel vents.
• A/C compressor on (the indicator lamp in the AC button comes on).
- Read the measured values for the A/C compressor regulator valve activation and the pressure measured by the A/C pressure/temperature sensor from vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding".
- Check the following displays:
• A current greater than 0.3 A is displayed (current flows via A/C compressor regulator valve, compressor is switched on)
• A duty cycle greater than 30% is displayed (the A/C compressor regulator valve is controlled, A/C compressor is switched on).
• Check the A/C compressor regulator valve activation if no current or insufficient current is displayed. Refer to => [ A/C Compressor Regulator Valve, Checking Switch-On Signal ] A/C Compressor Regulator Valve, Checking Switch-on Signal.
• The pressure in the refrigerant circuit measured by the A/C pressure/temperature sensor rises above the value when the A/C compressor is switched off.
• If the measure 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. (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 so that the temperature of the air downstream from 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 temperature, engine speed and vehicle voltage measured. 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, residual moisture in the refrigerant circuit can cause ice to build up on the A/C compressor regulator 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 recirculation button on the Climatronic control module (the indicator lamp in the Umluft button turns on).
- Set engine speed of 2000 rpm (start of time measurement).
- Read the measured value from the evaporator vent temperature sensor. Refer to vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding".
- Compare the evaporator vent temperature sensor measured value to the values in the diagram.
A Air temperature measured by the evaporator vent temperature sensor
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 Values Required Are Not Reached:
- Compare the Evaporator Vent Temperature Sensor measured value with the measured values from the Left Vent Temperature Sensor (G150) and the Right Vent Temperature Sensor (G151). Refer to vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding".
• If the measured from the Evaporator Vent Temperature Sensor deviates just a little from the left vent temperature sensor and the right vent temperature sensor measured values, then perform the procedure for identifying malfunctions if specified values are not reached. Refer to => [ Determining Malfunction if Specified Values Are Not Obtained ].
• If the measured value of evaporator vent temperature sensor is greater than the measured value of left vent temperature sensor and/or of right vent temperature sensor, then check the evaporator vent temperature sensor for proper installation and perform an electrical test on the sensor. Refer to vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding".
• The A/C system function can be recognized by both refrigerant pipes to or from the evaporator cooling off.
• If the Climatronic control module has been removed from the center console. The electrical connections cannot be separated for this purpose. If the refrigerant lines can be reached through the installation compartment, and their temperature can be felt with the hand (Climatronic control module, removing, refer to => [ Climatronic Control Module ] Climatronic Control Module). To feel, reach into the installation shaft in the instrument panel carefully (the coolant lines installed near the refrigerant lines may still be hot).
If the Measured Value for the Evaporator Vent Temperature Sensor (G263) (and Therefore the System Output) is OK:
- Compare the Evaporator Vent Temperature Sensor measured value with the measured values from the Left Vent Temperature Sensor and the Right Vent Temperature Sensor. Refer to vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding". 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.
The cooling performance test is completed when the required values are reached.
• If the required values are not reached, compare the displayed measured values for the left vent temperature sensor and right vent temperature sensor with each other. If the measured value in one or both display fields is not OK, check the activation and function of the left heat regulation valve, the right heat regulation valve and the Coolant Pump (V50). Refer to => [ Determining Malfunction if Temperature Increase Downstream from Evaporator ] and vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding".
• If the measured value from the left vent temperature sensor and/or from the right vent temperature sensor is lower than the measured value from the evaporator vent temperature sensor, then check the evaporator vent temperature sensor, the left vent temperature sensor and the right vent temperature sensor for proper installation and check their electrical connectors for contact resistance. Refer to vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding". Replace the faulty sensor if necessary.
• If the required values are not reached and there is no malfunction found on the left vent temperature sensor, right vent temperature sensor, Left Heat Regulating Valve (N175), Right Heat Regulating Valve (N176) and coolant pump, then determine the malfunction with temperature increase downstream of the evaporator. Refer to => [ Determining Malfunction if Temperature Increase Downstream from Evaporator ] and vehicle diagnosis, testing and information system VAS 5051/ under "Guided Fault Finding".
• The temperature of air flowing out of the center instrument panel vents can also be measured using a standard thermometer.
• A complaint regarding different air temperature detected from the vents in A/C regulated mode may result from air in the heat exchangers (varying air passage through the heat exchangers without uniform heating), refer to => [ Heat Output, Checking ] Heat Output, Checking. The foam seal may have come loose when installing the heat exchanger allowing air to flow past the heat exchanger. The A/C system refrigerant circuit is not filled with the correct quantity of refrigerant.
Determining Malfunction if Specified Values Are Not Obtained
Continue testing if the required values are not reached during the cooling performance test. Refer to => [ A/C Unit, Checking Cooling Output ] A/C Unit, Checking Cooling Output.
Continuation of test " Pressure in Refrigerant Circuit Increases"
• The pressure in the refrigerant circuit depends on several factors. However, in general, the pressure should not exceed 20 bar at an ambient temperature of 20 to 25 °C. Pressures up to 31 bar may occur due to extremely high performance under severe conditions (such as in southern countries with a hot climate, stop and go traffic and high humidity).
• At temperatures below 25° C, the pressure in the refrigerant circuit generally does not rise above 16 bar (the coolant fans run and cool the condensers down).
• The Climatronic Control Module (J255) controls the A/C compressor switching on and off via the measured value from the A/C Pressure/Temperature Sensor (G395). At an absolute pressure of less than approximately 1.8 bar or greater than approximately 32 bar, the Climatronic control module does not switch on the A/C compressor (the A/C Compressor Regulator Valve (N280) is not activated). The A/C compressor is only switched on once the absolute pressure becomes greater than 1.8 bar or less than 16 bar. Refer to Vehicle Diagnosis, Testing and Information System VAS 5051/ under "Guided Fault Finding".
• For additional information regarding pressure in the coolant circuit, refer to Vehicle Diagnosis, Testing and Information System VAS 5051/ under "Guided Fault Finding".
The A/C compressor output is controlled by the Climatronic control module so it does not have to be switched off automatically because the pressure in the refrigerant circuit or the coolant temperature is too high:
• As soon as the pressure in the refrigerant circuit exceeds 30 bar (absolute pressure), full compressor performance is only enabled again once the pressure has dropped below 27 bar.
• As soon as the coolant temperature goes above 115 °C (at 118 °C is switches off completely).
• If the pressure in the refrigerant circuit exceeds 32 bar despite regulation, the Climatronic control module switches the A/C compressor back on only when the pressure has dropped below 29 bar.
Determining Malfunction if Temperature Increase Downstream from Evaporator
Continue testing if the evaporator determines an increase in the temperature during the cooling performance test => [ A/C Unit, Checking Cooling Output ] A/C Unit, Checking Cooling Output.
