Cooling Output, Checking, Vehicles With Manual Climate Control System
Refer to INFORMATION ON CHECKING COOLING OUTPUT AND TOOLS REQUIRED
This service information only outlines the testing procedure. Perform the detailed function test for the heating 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.
-- Start the engine.
-- Switch off the A/C compressor on the A/C Control Module -J301- control head: the indicator lamp in the A/C button -2- does not illuminate.
-- "Read measured values" using the Vehicle Diagnostic Tester in the "Guided Fault Finding " function.
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 | Displayed Pressure |
|---|---|
| 15 °C (59 °F) | 3.0 bar (43.51 psi) |
| 20 °C (68 °F) | 4.0 bar (58.01 psi) |
| 25 °C (77 °F) | 5.0 bar (72.51 psi) |
| 30 °C (86 °F) | 6.0 bar (87.02 psi) |
| 35 °C (95 °F) | 7.0 bar (101.52 psi) |
At absolute pressure, 0 bar corresponds to absolute vacuum. Normal ambient pressure equals approximately 1 bar (14.5 psi) 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 Refrigerant Circuit Pressure Sensor -G805- signal using the Vehicle Diagnostic Tester in the "Guided Fault Finding " function.
If no fault can be detected on the Refrigerant Circuit Pressure Sensor -G805-, there is too little refrigerant in the circuit.
If the displayed pressure in the refrigerant circuit is OK:
-- Adjust the following settings on the A/C Control Module -J301- control head:
- Turn the temperature setting regulator -11- to the "cold" stop.
- Turn the air distribution regulator -7- to the "instrument panel vent" stop.
- A/C compressor on: The indicator lamp in the A/C button -2- illuminates.
- Recirculating air mode on: the indicator lamp in the recirculation button -4- illuminates.
- Turn the fresh air blower regulator -9- to the maximum speed.
-- "Read measured values" using the Vehicle Diagnostic Tester in the "Guided Fault Finding " function.
-- Check the information in the display fields:
- The current calculated by the A/C Control Module -J301-, 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, transfer the vehicle to a workshop that has the necessary tools and equipment and where the work can be performed by qualified personnel. Refer to WORKING ON REFRIGERANT CIRCUIT . Bring the detected problems to the attention of the workshop.
The A/C Control Module -J301- actuates the A/C Compressor Regulator Valve -N280- so that the air temperature reaches the specified value downstream of the evaporator (about 2 to 6 °C (35.6 to 42.8 °F)).
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 Temperature Sensor -G308- nears the specified 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 -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 actuation of the A/C Compressor Regulator Valve -N280- using the Vehicle Diagnostic Tester in the "Guided Fault Finding " function.
-- Press the Recirculation button -4- on the A/C Control Module -J301- control head.
- The indicator lamp in the button for the "recirculating air mode" illuminates.
-- Set the engine speed to 2000 rpm (start of time measurement).
-- "Read measured values" using the Vehicle Diagnostic Tester in the "Guided Fault Finding " function.
-- Compare the displayed measured value for the Evaporator Temperature Sensor -G308- with the values in the diagram.
A - Air temperature measured by the Evaporator Temperature Sensor -G308-
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 Temperature Sensor -G308-.
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 Temperature Sensor -G308- is greater than the determined measured value:
-- Make sure the Evaporator Temperature Sensor -G308- is installed correctly (refer to Evaporator Temperature Sensor -G308-, REMOVING AND INSTALLING ) and perform an electrical test for this sensor using the Vehicle Diagnostic Tester in the "Guided Fault Finding " function.
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.
If the measured value for the Evaporator Temperature Sensor -G308- and the A/C system cooling output is OK:
-- Measure the temperature of the air coming out of the left and right instrument panel vents with a thermometer.
-- Compare the measured values on the thermometer and for the Evaporator Temperature Sensor -G308-.
- The determined measured values must not be smaller than the value for the Evaporator Temperature Sensor -G308- and not greater than maximum 7 °C (44.6 °F) after five minutes.
If the determined measured values are smaller:
-- Make sure the Evaporator Temperature Sensor -G308- is installed correctly and check the electrical connections for contact resistance. Replace the 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 with the temperature increase 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.