Cooling Output, Checking
Test requirements are met, refer to TEST REQUIREMENTS .
-- Measure the ambient temperature (it must higher than 15 °C).
-- Close doors, hood, windows and sun roof.
-- Open all instrument panel vents.
-- Switch ignition on.
-- Switch off the A/C compressor via the AC -button (indicator lamp in AC -button does not light up).
-- Start the engine.
-- Initiate a Guided Fault Finding on the A/C system using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
-- Select Guided Fault Finding and read the following values (A/C Compressor Regulator Valve -N280- control and the High Pressure Sensor -G65-) measured value using Vehicle Diagnosis, Testing and Information System VAS 5051 under "Guided Fault Finding".
- The A/C compressor activation is switched off.
- The pressure in the refrigerant circuit is same as the measured outside temperature or greater than the value in the chart.
| Ambient temperature in °C | Pressure display (in bar absolute) |
|---|---|
| 15 | 4, 0 |
| 20 | 5, 0 |
| 25 | 6, 0 |
| 30 | 7, 0 |
| 35 | 8, 0 |
- In terms of absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure equals approximately 1 bar absolute pressure. 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).
- Pressure in refrigerant circuit is governed by ambient temperature. On account of heat given off by components (e.g. radiator), pressure displayed with warm engine will be slightly higher than that given for the respective ambient temperature.
- Only integer values are displayed for the pressure in refrigerant circuit in the measuring value block of A/C control module, if the value measured lies between two values the display switches back and forth.
If the displayed pressure in the refrigerant circuit is lower than in the table:
- Check the high pressure sensor signal, refer to HIGH PRESSURE SENSOR, 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, refer to PRESSURES, CHECKING .
If pressure in refrigerant circuit is OK (the same or greater than specified in the table)
-- Switch on the A/C compressor, to do so press the AC -button on A/C control module (indicator lamp in AC comes on)
-- Set the lowest possible temperature (turn the temperature rotary switch all the way to cold).
-- Set the air flow direction to instrument panel vents via the air distribution rotary switch.
-- Set speed 4 on fresh air blower rotary switch.
-- Switch A/C system to recirculating air mode by pressing recirculating air mode button on (indicator lamp in recirculating air button comes on).
-- Select "Guided Fault Finding" and read the following values using Vehicle Diagnosis, Testing and Information System VAS 5051.
- The A/C control module calculate the current that is flowing via the A/C Compressor Regulator Valve and is greater than 0.3 Amps (the A/C compressor is on).
- The displayed pressure increases above the value when the compressor is switched off.
- If the displayed pressure does not change and the A/C compressor control is OK, then check the calculated pressure one more time via the A/C Compressor regulator valve and make sure the A/C compressor is actually being driven by the /C Compressor regulator valve, then there is 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 PRESSURES, CHECKING (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 controlled by the A/C control module so that the air temperature after the evaporator reaches the specified value (approximately 2 to 5 °C).
- After starting the engine, and depending on the measured temperature, the engine RPM and the voltage for the A/C Compressor regulator valve, a value greater than 055 Amps is displayed. As soon as the temperature measured by evaporator vent temperature sensor 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 (and on the expansion 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 .
If the A/C compressor regulator valve measured blocks value, or if no current or very little current is displayed, check the A/C compressor regulator valve control A/C COMPRESSOR REGULATOR VALVE, CHECKING SWITCH-ON SIGNAL .
-- Press button for recirculating air mode on A/C control module (indicator lamp for recirculating air mode in button lights up).
-- Set engine speed of 2000 rpm (start of time measurement).
-- Select "read measured values block" using Vehicle Diagnosis, Testing and Information System VAS 5051 under "Guided Fault Finding".
-- Compare the displayed measured value evaporator vent temperature sensor) to 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 required values have not been reached, measure temperature of the air flowing out of instrument panel vents using a thermometer. Compare this value with the displayed measured value of evaporator vent temperature sensor. If both measure values deviate only slightly from one another, perform malfunction identification when specified value is not reached, refer to DETERMINING MALFUNCTION IF SPECIFIED VALUES ARE NOT OBTAINED . If the measured value from the evaporator vent temperature sensor is larger than your measured value, then make sure the evaporator vent temperature sensor is installed correctly and perform an electrical test on the sensor. Refer to Vehicle Diagnosis, Testing and Information System VAS 5051 under "Guided Fault Finding".
- The function of the air conditioning is recognizable, e.g. the refrigerant pipe on the low pressure side (thick line) cools off.
If the measured value for the evaporator vent temperature sensor (and therefore the system output) is OK:
-- Measure temperature of the air flowing out of left and right instrument panel vents using a thermometer.
-- Compare your measured values (Left Vent Temperature Sensor -G150-, Right Vent Temperature Sensor -G151- and evaporator vent temperature sensor). The measured values may not be smaller and after 5 minutes be greater than maximum 3 °C, than the value of the evaporator vent temperature sensor.
- If the measured value are smaller, make sure the evaporator vent temperature sensor is installed correctly and check the electrical connections for contact resistance; replace the sensor if it is defective. Refer to Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
- If the required values are not reached on one or both sides, then check the temperature door control and function. Perform a malfunction search if the temperature rises, refer to TEMPERATURE INCREASE DOWNSTREAM FROM EVAPORATOR, DETERMINING MALFUNCTION and Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding".
- Problems relating to differences between temperature of air emitted by left and right vents with identical setting in air conditioner regulated mode may have the following causes: One of the temperature doors in air distribution housing does not close completely or does not reach its end position AIR GUIDE IN EVAPORATOR HOUSING and Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function. There is air in the heater cores (fluctuating flow through heater core and heat is not distributed uniformly) HEATING PERFORMANCE OF A/C SYSTEM, CHECKING or a foam seal was loosened during installation of the heater core and air may bypass the heater core.