Cooling Output, Checking, Vehicles With Manual Climate Control System
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 Guided Fault Finding. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the Climatronic Control Module -J255-).
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.
-- 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.
- Switch off the A/C compressor on the Front A/C Display Control Head 3 -E776- -2- : The indicator lamp in the A/C button (in the regulator -2-) does not come on.
-- Switch off the A/C compressor on the Front A/C Display Control Head 3 -E776- -2- : The indicator lamp in the A/C button (in the regulator -2-) does not come on.
-- Select the "Read measured values" function 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 A/C system control heads:
- Turn the regulator -1- (Front A/C Display Control Head 2 -E775-) for the fresh air blower to the maximum speed.
- Turn the regulator -2- (Front A/C Display Control Head 3 -E776-) for the temperature setting to the "cold" stop.
- Turn the regulator -3- (Front A/C Display Control Head 4 -E777-) for air distribution to "instrument panel vent".
- A/C compressor on: The indicator lamp in the A/C button (in regulator -2-) illuminates.
-- "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:
- The current calculated by the Climatronic Control Module -J255-, which flows 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 calculated current is actually flowing via the A/C Compressor Regulator Valve -N280- and the A/C compressor is actually being driven.
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 or LAWS AND REGULATIONS . 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 (75%) 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 thereby 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 -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 little or no 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-).
-- Switch on the recirculating air mode at the Fresh Air and Recirculating Air Mode Button -E781-.
- The indicator lamp for "recirculating air mode" in the button -4- illuminates.
-- 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.
-- 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:
-- Measure the temperature of the air coming out of the left and right instrument panel vents with a thermometer.
-- Compare the measured value with the displayed measured value for the Evaporator Vent Temperature Sensor -G263-.
If the measured values 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 determined measured value:
-- 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 from the inner heat exchanger to the A/C compressor) cooling off. Refer to SYSTEM OVERVIEW - REFRIGERANT CIRCUIT .
If the measured value for the Evaporator Vent Temperature Sensor -G263- and the A/C system cooling output is OK:
-- Measure the temperature of the air coming out of the left -1- and right -2- instrument panel vents with a thermometer.
-- Compare the measured values on the thermometer and for the Evaporator Vent Temperature Sensor -G263-.
- The determined measured values must not be smaller than the value for the Evaporator Vent Temperature Sensor -G263- and also not greater than a maximum of 7 °C (44.6 °F) after five minutes.
If the determined measured values are smaller:
-- Make sure the Evaporator Vent Temperature Sensor -G263- is installed correctly and check its connectors for contact resistance. Replace a faulty sensor. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
If the requested values are not reached:
-- Check the actuation and function of the temperature control door. To do so, determine the malfunction when the temperature increases downstream of the evaporator. Refer to DETERMINING MALFUNCTION OF TEMPERATURE INCREASE DOWNSTREAM FROM EVAPORATOR and use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the Climatronic Control Module -J255-).