A/C refrigerant system cooling performance, testing: Checking
- - Measure ambient temperature (must greater than 15 °C).
- - Close doors, hood, window and sunroof.
- - Open all dash panel vents.
- - Switch ignition on.
- - Select ECON mode on A/C control head -E87- (indicator light in ECON button lights up).
- - Start engine.
- - Initiate On Board Diagnostic (OBD) of air conditioner. See VAS 5051 VEHICLE DIAGNOSTIC, TESTING AND INFORMATION SYSTEM, CONNECTING AND SELECTING FUNCTIONS .
- - Select READ MEASURING VALUE BLOCK (FUNCTION 08) , DISPLAY GROUP 001: .
- - Check indication in display fields:
- - Display field "2" shows 0% (compressor is switched off)
- - Display field "4" shows, that the pressure in the refrigerant circuit measured at ambient temperature is the same or greater as the table value.
INDICATION IN DISPLAY FIELD 4
| Ambient temperatures in °C | Displayed pressure (in bar absolute pressure) |
|---|---|
| 15 | 4.7 |
| 20 | 5.6 |
| 25 | 6.6 |
| 30 | 7.6 |
| 35 | 8.8 |
NOTE:
- At absolute pressure, 0 bar corresponds to absolute vacuum. Normal ambient pressure corresponds to approximately 1 bar absolute pressure. 0 pressure corresponds to an absolute pressure of one bar on most pressure gauges (indicated by -1 below 0).
- The pressure in the refrigerant circuit depends on the ambient temperature. Via heat emission of components (e.g. coolant fan), with the engine at operating temperature a slightly higher pressure is displayed as for the respective ambient temperature.
- If the displayed pressure is lower than in the table:
- - Check measuring value of High Pressure Sensor - G65-. See READ MEASURING VALUE BLOCK (FUNCTION 08) and TEST STEPS 5 TO 9 "electrical testing, test step 5".
- - If no malfunction can be detected on high pressure sensor, there is not enough refrigerant in the circuit.
If the pressure in the refrigerant circuit is OK.
- - Switch compressor on, for this select "Auto" mode on A/C control head -E87- (indicator light in "ECON" button does not light up).
- - Select temperature mode "Lo" (for driver's and passenger's side) on A/C Control Head -E87-.
- - Select air flow direction on A/C Control Head -E87- to "air from dash panel vents"
- - Select READ MEASURING VALUE BLOCK (FUNCTION 08) , DISPLAY GROUP 001: .
- - Check indication in display fields:
- - Display field "2" shows a duty cycle greater than 30% (A/C Compressor Regulator Valve -N280- is activated, compressor is switched on)
- - Display field "1" shows a current greater than 0.3 A (current flows via A/C Compressor Regulator Valve -N280-, compressor is switched on)
- - The shown pressure in display field "4" rises above the value with the compressor switched on.
NOTE:
- A/C Compressor Regulator Valve -N280- is activated by A/C Control Head -E87- so that the air temperature after evaporator reaches the specified value (approx. 2 to 5 °C). A value 75% (0.55 A) greater is displayed after engine start depending on the measured temperature, engine speed and voltage supply. As soon as the measured temperature from Evaporator Vent Temperature Sensor -G263- approaches the specified value, the activation is reduced and the compressor performance is decreased.
- Under certain operating conditions, residual moisture in refrigerant circuit can lead to an ice build-up at the compressor regulator valve. Compressor control is reduced by this ice build-up, evaporator is cooled too intensely and freezes. The freeze-up of the evaporator can be the cause for the following customer complaints:
- - After a long drive, A/C system repeatedly or sporadically fails (no cooling or heating performance), after switching off vehicle and after a short time, A/C function is OK again.
- - After a long drive, windows fog up from inside, windows are also not cleared by pressing the "Defrost" button, after switching off vehicle and after a short time, A/C function is OK again.
Repair steps:
- - Check measured value of Evaporator Vent Temperature Sensor -G263-. See READ MEASURING VALUE BLOCK (FUNCTION 08) , DISPLAY GROUP 010: . If measured value of the sensor is too low under operating conditions specified by Service (at an ambient temperature above 0° C, colder than 0° C for a long period of time although A/C Compressor Regulator Valve -N280- is not activated at the time), perform the following work steps (discharge refrigerant circuit, replace accumulator and then evacuate refrigerant circuit for a minimum of 3 hours).
- - Check refrigerant line from evaporator to accumulator (thick tube, low pressure side) with engine running. If this line is thickly iced-up when complaint occurs (a very thin layer of ice is permitted), this indicates that the temperature in evaporator is too low.
- - If the measuring value of the sensor is too high for the operating requirements described by the customer (higher than e.g. 10° C even though the A/C system is functioning properly) check Evaporator Vent Temperature Sensor - G263- (the condenser can ice over due to an incorrect measuring value).
- - If the measuring value of the sensor is too low for the operating requirements described by the customer (at an ambient temperature above 0° C, it is colder than 0° C for an extended period of time even though A/C Compressor Regulator Valve -N280- is not currently being activated) Take vehicle to a dealership which services A/C systems.
- - - Check refrigerant line from condenser to accumulator (thick line, low-pressure side) with the engine running. If this line is strongly iced over when the complaint condition occurs (a thin layer of ice is permissible) this also indicates that the temperature in condenser is too low.
- - - If necessary, make the climate control supporting workshop aware of the determined deficiency if necessary, the required work can only be performed there (empty refrigerant circuit, replace accumulator and then evacuate refrigerant circuit for at least 3 hours).
- If display field "1" shows no or not enough current, check activation of A/C Compressor Regulator Valve. See TEST STEPS 5 TO 9 "Electrical testing test step 6".
- If the shown pressure in display field "4" does not change and the activation of the compressor is OK (display field "1" and "2"), the refrigerant circuit has a malfunction.
- - Press button for "air recirculation" (symbol for "air recirculation" mode button is lit up).
- - Increase engine speed to 2000 RPM (timed period begins).
- - Select READ MEASURING VALUE BLOCK (FUNCTION 08) , DISPLAY GROUP 010: .
- - Compare displayed measuring value (of Evaporator Vent Temperature Sensor -G263-) in display field "1" with values in diagram.
- A - Measured air temperature of Evaporator Vent Temperature Sensor -G263-
- B - Ambient temperature
- C - Permissible tolerance
Depending on the ambient temperature, the measured air temperature should be after 5 minutes within the shown tolerance range.
NOTE:- If the required values are not obtained, check the measuring value of Evaporator Vent Temperature Sensor - G263-, compare shown measuring values in display group "010" display field "1" and display group "009" display fields "3" and "4" with each other.
- - If the measuring value in both display fields "3" or "4" deviates only slightly from the measuring value in display group "010", Carry out "Identifying malfunctions if specified values are not obtained". See IDENTIFYING MALFUNCTIONS IF SPECIFIED VALUES ARE NOT OBTAINED .
- - If the measuring value of Evaporator Vent Temperature Sensor -G263- is greater than Left Vent Temperature Sensor -G150- and Right Vent Temperature Sensor -G151-, check - G263- for correct installation and carry out electrical testing for this sensor. See TEST STEP 2: .
- The function of the air conditioning is recognizable, e.g. the refrigerant pipe on the low pressure side (big line) cools off.
If the measuring value of Evaporator Vent Temperature Sensor -G263- is OK (and therefore the cooling performance of the air conditioning system).
- - Compare the measuring value (of Evaporator Vent Temperature Sensor -G263-) in display group "010" display field 1 with the measuring values of display group "009" display fields "3" and "4" (-G150- and -G151-).
After 5 minutes, the measuring values in display group "009" display field "3" and "4" (-G150- and -G151-) can be maximum 3° C greater than the value in display field "1" of display group "010" (of Evaporator Vent Temperature Sensor -G263-).
NOTE:- If the required values are not obtained, compare displayed measuring values in display group "009" display fields "3" and "4" with each other:
- - If the measuring value in one the two display fields "3" or "4" is OK. Check positioning motor for temperature flap on the side where the measuring value is not OK (Actuator for temperature flap left -V158- or Actuator for temperature flap right -V159-). See TEST STEP 2: .
- - If the measuring value in display group "009" display fields "3" or "4" is lower than the measuring value in display group "010" display field "1", check Evaporator Vent Temperature Sensor -G263-, Left Vent Temperature Sensor -G150- and Right Vent Temperature Sensor -G151- for correct installation and their electrical connections for contact resistance, if necessary replace faulty sensor.
- - If no malfunction is detected on -G150- and -G151-, as well as on -V158- and -V159-, carry out IDENTIFYING MALFUNCTIONS AT TEMPERATURE INCREASE BEHIND CONDENSER .
- The air temperature of the center dash panel vents can be measured e.g. using the V.A.G 1362 mini tester.
- The measuring values of Left Footwell Vent Temperature Sensor -G261- and Right Footwell Vent Temperature Sensor -G262- are shown in display group "009", display fields "1" and "2". The two sensors show an incorrect value, because in "AUTO" mode most of the air flow is directed to the dash panel vents. By pressing the "Air to footwell" button, these sensors can also be checked in this test.