Cooling Output, Checking, Vehicles With Automatic Climate Control System
Refer to INFORMATION ON CHECKING COOLING OUTPUT AND TOOLS REQUIRED
This Service Information only outlines the testing procedure. Perform the detailed test for this heating and A/C system function as described in the Guided Fault Finding using the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
Procedure
- The cooling output test requirements are met. Refer to TEST REQUIREMENTS .
-- Measure the ambient temperature: It must be greater than 15 °C (59 °F).
-- Close the doors, hood, windows, sliding sunroof and rear lid.
-- Open all instrument panel vents and, if equipped, the vents in the rear center console.
-- Start the engine.
-- Adjust the following settings on the A/C system control heads:
This illustration shows the layout of the regulators -1, 2 and 3- and the buttons -4 and 5- on a LHD vehicle. The layout may be different on RHD vehicles.
The information in the regulators -1, 2 and 3- is only displayed when the ignition is switched on and goes out when the ignition is switched off.
- Switch off the A/C compressor on the Front A/C Display Control Head 2 -E775- -1- : The indicator lamp in the A/C button (in the regulator -1-) does not come on.
-- "Read the measured values" using the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the Climatronic Control Module -J255-).
Checking
-- Read the activation of the A/C Compressor Regulator Valve -N280-.
- The activation of the A/C compressor (by the A/C Compressor Regulator Valve -N280-) is switched off: 0 A (amps) or 0% will be displayed.
-- Read the measured value for the Refrigerant Circuit Pressure Sensor -G805-.
- The refrigerant circuit pressure is same at the measured ambient temperature or is greater than the value in the table.
| Ambient Temperature in °C (°F) | Displayed Pressure (Pressure in bar) |
|---|---|
| 15 (59) | 3.0 |
| 20 (68) | 4.0 |
| 25 (77) | 5.0 |
| 30 (86) | 6.0 |
| 35 (95) | 7.0 |
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).
Pressure in refrigerant circuit is governed by the ambient temperature. Due to the heat given off by components (for example, the radiator), the pressure displayed with a 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 the signal for the Refrigerant Circuit Pressure Sensor -G805- using the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the Climatronic Control Module -J255-).
If no fault can be detected on the Refrigerant Circuit Pressure Sensor -G805-, there is too little refrigerant in the circuit.
-- The necessary work procedures may only be performed by qualified personnel. If this is not possible, bring the vehicle to a workshop that has the necessary tools and in which the work can be performed by qualified personnel. Refer to A/C SYSTEM, GENERAL INFORMATION or LAWS AND REGULATIONS . Bring the detected problems to the attention of the workshop.
If the displayed pressure in the refrigerant circuit is OK:
-- Adjust the following settings on the Climatronic Control Module -J255- control head:
- "Auto" mode on: The indicator lamp in the Auto button (in the regulator -2-) illuminates.
- Turn the regulator -2- (Front A/C Display Control Head 3 -E776-) for the temperature setting to the "cold" stop.
- A/C compressor on: The indicator lamp in the A/C button (in regulator -1-) illuminates.
- Turn the regulator -1- (Front A/C Display Control Head 2 -E775-) for the fresh air blower to the maximum speed.
- Turn the regulator -3- (Front A/C Display Control Head 4 -E777-) for air distribution to "instrument panel vent".
- Recirculating air mode off: The indicator lamp for "recirculating air mode" in the Recirculation button (in the regulator -3-) does not come on.
- Defrost mode off: The indicator lamp in the Defrost Button -E782- -4- does not come on.
-- "Read the measured values" using the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the Climatronic Control Module -J255-).
-- Check the information in the display fields:
- If a displayed current that is flowing via the A/C Compressor Regulator Valve -N280- is greater than 0.3 amps (30%): the A/C compressor is switched on.
- The displayed pressure goes over the value when the A/C compressor is switched off.
If the displayed pressure does not change and the activation of the A/C compressor is OK:
-- Check once more if the A/C compressor is actually being driven and the A/C Compressor Regulator Valve -N280- is being activated.
If the current is actually flowing via the A/C Compressor Regulator Valve -N280- and the A/C compressor is being driven, then the fault is in the refrigerant circuit. It is possible that the A/C compressor regulation is not OK.
-- The necessary work procedures may only be performed by qualified personnel. If this is not possible, bring the vehicle to a workshop that has the necessary tools and in which the work can be performed by qualified personnel. Refer to A/C SYSTEM, GENERAL INFORMATION and LAWS AND REGULATIONS (the A/C compressor regulation may not be OK). Bring the detected problems to the attention of the workshop.
The Climatronic Control Module -J255- actuates the A/C Compressor Regulator Valve -N280- so that the air temperature reaches the specified value downstream of the evaporator (approximately 2 to 6 °C).
After starting the vehicle, a value greater than 0.55 A is displayed for the activation of the A/C Compressor Regulator Valve -N280- depending on the measured temperature, the engine speed and the electrical system voltage. As soon as the temperature measured by the Evaporator Vent Temperature Sensor -G263- nears the specified value, the activation is canceled and the A/C compressor output is reduced as a result.
Under certain operating conditions, moisture in the refrigerant circuit can lead to ice build-up on the A/C Compressor Regulator Valve -N280- and on the expansion valve. This ice build-up interferes with A/C compressor regulation. The evaporator is cooled too intensely and freezes. The freeze-up of the evaporator can be the cause for various customer complaints. Refer to LOCALIZING MALFUNCTION FOR ICE BUILD-UP ON EVAPORATOR .
If no or very little current is displayed in the measured values for the A/C Compressor Regulator Valve -N280- activation, check the activation of the A/C Compressor Regulator Valve -N280-. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the Climatronic Control Module -J255-).
-- Press the Recirculation button (in the regulator -4-) on the Front A/C Display Control Head 4 -E777-.
- The indicator lamp for "recirculating air mode" in the Recirculation button (in the regulator -3-) illuminates.
- Defrost mode off: The indicator lamp in the Defrost Button -E782- -4- does not come on.
-- Set the engine speed to 2000 RPM (start of time measurement).
-- "Read the measured values" using the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the Climatronic Control Module -J255-).
-- Compare the displayed measured value for the Evaporator Vent Temperature Sensor -G263- with the values in the diagram.
A - Air temperature measured by the Evaporator Vent Temperature Sensor -G263-
B - Ambient Temperature
C - Permissible Tolerance Range
- Depending on the ambient temperature, the measured air temperature must be within the specified tolerance range after 5 minutes.
If the requested values are not reached:
-- Compare the measured values for the Left Vent Temperature Sensor -G150- (or the Right Vent Temperature Sensor -G151-) with the displayed measured value for the Evaporator Vent Temperature Sensor -G263-. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the Climatronic Control Module -J255-).
-- Measure the temperature of the air coming out of the right instrument panel vent -2- with a thermometer (left vent on a RHD vehicle).
The designation and the component location of the vent temperature sensors (Left Vent Temperature Sensor -G150- and Right Vent Temperature Sensor -G151-) is different. The Left Vent Temperature Sensor -G150- is installed in the air duct to the left instrument panel vent -1- on LHD vehicles. The Right Vent Temperature Sensor -G151- is installed in the air duct to the right instrument panel vent -2- on RHD vehicles.
The temperature of the air coming out of the left -1- and right -2- instrument panel vents can also be measured with a thermometer.
If the measured values of the Evaporator Vent Temperature Sensor -G263- and Left Vent Temperature Sensor -G150- (or Right Vent Temperature Sensor -G151-) only slightly deviate from each other:
-- Perform the procedure for identifying malfunctions if there is a deviation from the specified value. Refer to DETERMINING MALFUNCTION IF DEVIATION FROM SPECIFIED VALUE .
If the measured value for the Evaporator Vent Temperature Sensor -G263- is greater than the measured value for the Left Vent Temperature Sensor -G150- (or Right Vent Temperature Sensor -G151-):
-- Make sure the Evaporator Vent Temperature Sensor -G263- is installed correctly (refer to Evaporator Vent Temperature Sensor -G263-, REMOVING AND INSTALLING ) and perform an electrical test for this sensor. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the Climatronic Control Module -J255-).
The A/C system function can be recognized, for example, by the refrigerant pipe on the low pressure side (thick line) cooling off.
If the measured value for the Evaporator Vent Temperature Sensor -G263- and the A/C system cooling output is OK and there are no complaints, the cooling output test ends.
If the measured value for the Evaporator Vent Temperature Sensor -G263- (and the A/C system cooling output) is not OK:
-- Perform the procedure for identifying malfunctions if there is a deviation from the specified value (requested cooling output is not reached). Refer to DETERMINING MALFUNCTION IF DEVIATION FROM SPECIFIED VALUE .
If the measured value for the Evaporator Vent Temperature Sensor -G263- (and the A/C cooling output) is OK and there is a complaint regarding excessive or different vent temperatures for the heating and A/C system:
-- Check the activation of the temperature control doors in the heater and A/C unit. Refer to AIR DISTRIBUTION HOUSING, REMOVING AND INSTALLING and use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the Climatronic Control Module -J255-).