A/C System Cooling Performance, Checking
- Test requirements are met, refer to TEST REQUIREMENTS .
-- Measure the ambient temperature (it must higher than 15 °C (59 °F)).
-- Close doors, hood, windows and sun roof.
-- Open vents of instrument panel, in rear center console and in B and C pillars (on vehicles with a rear A/C system).
-- Open instrument panel vents (on vehicles without rear A/C system, vents in rear center console and in B pillar remain closed)
-- Switch ignition on.
-- Set operating mode Econ (on the Climatronic Control Module -J255- or on MMI). Refer to Owner's Manual and Owner's Manual / Infotainment/MMI.
Depending on the version of the Climatronic control module it is possible to recognize if Econ is on if the indicator lamp in the button Econ is on and in the AC or A/C button off.
-- Start the engine.
-- Initiate Guided Fault Finding of the Climatronic control module of A/C system using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
-- Select "Read measuring value block" function and read out values in the following display groups and Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
- The compressor activation via the A/C Compressor Regulator Valve -N280- is switched off (the compressor is switched off and 0% is shown in the display field).
- The pressure in the refrigerant circuit determined by the High Pressure Sensor -G65- is the same or greater than the value in the table at the measured ambient temperature.
| Ambient temperature in °C (°F) | Pressure display (in bar absolute) (PSI) |
|---|---|
| 15 (59 °F) | 4.0 (43.5) |
| 20 (68 °F) | 5.0 (58) |
| 25 (77 °F) | 6.0 (72.5) |
| 30 (86 °F) | 7.0 (87) |
| 35 (95 °F) | 8.0 (101.5) |
In terms of absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure equals approximately 1 bar absolute pressure (14.5 psi). 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 (for example, 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 signal of High pressure sensor, refer to HIGH PRESSURE SENSOR G65, CHECKING PRESSURE SIGNAL . If no malfunction can be detected at High pressure sensor, there is insufficient 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. .
If pressure in refrigerant circuit is OK:
-- Switch on compressor, to do this select operating mode Auto on Climatronic control module (on Comfort version) or switch off operating mode Econ (on Basic version).
-- Set temperature preselect Lo for driver's and front passenger's side or set temperature rotary switch of Climatronic control module to cold stop (depending on A/C system version).
-- Set direction of air flow to instrument panel vents on Climatronic control module.
-- Select "read measured values block" using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
-- Check the indicators in the various display fields on the tester display:
- A duty cycle greater than 30% is shown in the display field for the A/C compressor regulator valve -N280- activation (the A/C compressor regulator valve is activated, when the compressor is switched on).
- Current greater than 0.3 A is shown in the display field for the current to the A/C compressor regulator valve (the current flows via the A/C compressor regulator valve when the compressor is switched on).
- The pressured measured by the high pressure sensor and display increases over the value with the compressor switched off.
A/C compressor regulator valve is activated by the Climatronic control module so that temperature of air downstream of evaporator in front heating & A/C unit reaches the specified value (approximately 2 to 5 °C (35 to 41 °F)):
After vehicle start, depending on temperature, engine speed and vehicle voltage in the measured value block, a value greater than 75 % (0.55A) is displayed for activation of the A/C Compressor Regulator Valve.
As soon as the temperature measured by evaporator vent temperature sensor -G263- approximates the specified value, activation of the A/C Compressor Regulator Valve is reduced and thus the compressor output is reduced.
If the pressure measured and displayed in the high pressure sensor does not change and compressor activation is OK, check whether the compressor is actually being driven (an overload protection is installed between the compressor and the belt pulley/drive unit. The compressor will not be driven if it has been triggered). If no malfunction is found, 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. Refer to A/C Compressor -G111- (it is possible that compressor regulation is not OK). Bring the problems determined to the attention of the workshop.
The connector to A/C Compressor Regulator Valve and the connector to the electric engine mounts are identical in construction. If these connectors are interchanged, no entry appears in DTC memory, however since the compressor is continuously actuated (by the engine control module), the evaporator may ice-up.
-- Press button for recirculating air mode on the Climatronic control module (symbol for recirculating air mode lights up in button).
-- Set engine speed of 2000 rpm (start of time measurement).
-- Select the display group with the evaporator vent temperature sensor in the "Read measured values block" function using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
-- Compare the displayed value (of the evaporator vent temperature sensor) with the values in the diagram.
A -
Measured air temperature of 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 specified values are not reached, check the measured value on the evaporator vent temperature sensor. Compare the displayed measured values on the evaporator vent temperature sensor, on the left front upper body vent temperature sensor -G385- and on the right front upper body vent temperature sensor -G386- (possible only on Comfort). For Basic version, measure temperature of the air flowing out of instrument panel vents using a thermometer.
- Do the measured values from the left front upper body vent temperature sensor and the right front upper body vent temperature sensor (Comfort A/C system) or the values measured with a thermometer (Basis A/C system) differ slightly from the measured value from the evaporator vent temperature sensor (less than 5° C (41 °F)) using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" . Perform the procedure for identifying malfunctions if specified values are not reached, refer to DETERMINING MALFUNCTIONS 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 vent temperature sensor and/or of from the right front upper body vent temperature sensor (Comfort A/C system) or the values measured with a thermometer (Basis A/C system), then make sure the evaporator vent temperature sensor is installed correctly and perform an electrical test on this sensor using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
The function of the air conditioning is recognizable, for example, the refrigerant pipe on the low pressure side (thick line) cools off.
If the measuring value of evaporator vent temperature sensor (and therefore the cooling performance of the A/C system) is OK.
-- Compare the displayed value from the evaporator vent temperature sensor with the measured valued from left front upper body vent temperature sensor and right front upper body vent temperature sensor (only Comfort) using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
For vehicles with Basic version A/C system, measure temperature of the air flowing out of instrument panel vents using a thermometer.
- Do the measured values from the left front upper body vent temperature sensor and the right front upper body vent temperature sensor (Comfort A/C system) or the values measured with a thermometer (Basis A/C system) may be greater than maximum 5 °C (41 °F) after 5 minutes than the measured value from the evaporator vent temperature sensor (less than 5° C (41 °F)). Check using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
The air travelling from evaporator to vents is heated slightly by heat radiated by heater core in heating & A/C unit and by leaking air which flows by at temperature doors through the heater core.
- If the required values are not reached, then compare the displayed measured values from the left front upper body vent temperature sensor and from the right front upper body vent temperature sensor (Comfort) with each other (on the Basis measure the temperature of the air coming out of the vents on the right and left sides of the instrument panel). If the measured value of one of the two sensors (of left front upper body vent temperature sensor and of right front upper body vent temperature sensor or the left or right measured value) OK and the measured value of the other one too large. Check the activation and the function of the temperature doors in the A/C unit (activation of the left temperature door motor -V158- and of the right temperature door motor -V159- as well as the lever, refer to RETAINING PLATE WITH LEFT FOOTWELL DOOR MOTOR -V108- AND LEFT TEMPERATURE DOOR MOTOR -V158- and RETAINING PLATE WITH CONTROL MOTORS -V158- / -V159- AND -V109- / -V108- ) and Vehicle Diagnosis, Testing and Information System VAS 5051 in"Guided Fault Finding" .
- The measured value of the left front upper body vent temperature sensor and of the right front upper body vent temperature sensor or the temperature of the air coming out of the vents) is lower than the displayed measured value of the evaporator vent temperature sensor. Make sure the evaporator vent temperature sensor (and on the Comfort the left front upper body vent temperature sensor and the right front upper body vent temperature sensor) are installed correctly and check the electrical connectors for contact resistance. Replace the faulty sensor if necessary, refer to Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
If no malfunction can be detected at evaporator vent temperature sensor, at Left Front Upper Body Outlet Temperature Sensor -- or Right Front Upper Body Outlet Temperature Sensor --, determine malfunction during temperature increase downstream of evaporator, refer to DETERMINING MALFUNCTION DURING TEMPERATURE INCREASE DOWNSTREAM OF FRONT EVAPORATOR .
On Comfort version, temperature of air flowing out of center instrument panel vents can also be measured for example, using a standard thermometer.
If there is a complaint of a different temperature of air from vents in A/C system regulated mode at the same setting in regulated mode, the causes for this may be for example, air in the heater core or a temperature door (a temperature door in heating & A/C unit is not opening or closing completely or is not reaching its end position), refer to AIR DUCT IN FRONT HEATING & A/C UNIT and Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.