A/C Refrigerant System, Testing
A/C Refrigerant System, Testing
A/C refrigerant system cooling performance, testing
Special tools and equipment
- VAS 5051 Vehicle Diagnostic, Testing and Information System (or V.A.G 1551 Scan Tool or V.A.G 1552 Scan Tool with V.A.G 1551/3 adapter cable) and if necessary V.A.G 6017 in case more vehicle systems are to be checked.
- V.A.G 1362 tester (for temperature measurement)
Test requirements:
- The ambient temperature is greater than 15 degrees C.
- Radiator and condenser are clean (clean if necessary)
- The ribbed belt for compressor drive is OK and properly tightened.
- All air ducts, covers and seals OK and properly installed.
- Air flow through dust and pollen filter not obstructed by dirt.
- Vehicle not standing in direct sunlight.
- Engine at normal operating temperature
- DTC memory checked, all displayed malfunctions eliminated and DTC memory was erased.
- The coding was checked and if necessary corrected and Read Measuring Value Block.
- The basic setting was carried out.
- All instrument panel vents open.
- The hood is closed.
- Settings on A/C Control Head -E87-:
- AUTO mode
- Temperature selection LO (for both driver's and passenger's side)
- Compressor on (indicator light in "Econ" button does not come on).
- Functions with engine running:
- Coolant Fan -V7- is running (speed depends on pressure in refrigerant circuit and engine temperature).
- Fresh Air Blower -V2- runs at maximum speed.
- The air conditioner goes in recirculated air mode (approx. 1 minute after starting the vehicle the fresh/back pressure flaps will be closed and the recirculated air flap will open, the Fresh Air Blower -V2- sucks the air from the passenger footwell).
NOTE: Check DTC memory if a test requirement is not obtained and carry out an output Diagnostic Test Mode (DTM).
Checking
- Measure ambient temperature (must greater than 15 degrees 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
- 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.
Ambient Displayed pressure (in
temperatures in degrees C 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- "Read Measuring Value Block" and "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 degrees 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 buildup, 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- "Read measuring value block" display group "010". If measured value of the sensor is too low under operating conditions specified by Service (at an ambient temperature above 0 degrees C, colder than 0 degrees 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 display field "1" shows no or not enough current, check activation of A/C Compressor Regulator Valve "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".
- 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 "Electrical testing, 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-) "electrical testing, 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 malfunction at temperature increase after evaporator".
- 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.
Identifying malfunctions if specified values are not obtained
- Select "Read Measuring Value Block" function 08 display group "001".
- Repeat A/C system cooling performance test.
- Observe during the cooling performance test display field "1" and "4". Was the activation of A/C Compressor Regulator Valve -N280- during the cooling performance test switched off (control current was less than 0.55 A)?
Part 1:
Continuation of test - Pressure in refrigerant circuit increases
- Open hood.
- Repeat A/C system cooling performance test.
- Does the Coolant Fan -V7- run during cooling performance test (speed depends on coolant temperature and pressure in refrigerant circuit, speed is determined by Engine Control Module (ECM))?
Part 2:
NOTE:
- The pressure in the refrigerant circuit depends on various factors. However, at an ambient temperature between 20 to 25 degrees C the pressure should not exceed more than 20 bar. Due to high coolant performance, pressures up to 31 bar may occur under extreme operating conditions (e.g. in southern countries with high ambient temperatures, "stop and go" traffic and high humidity).
- The pressure in the refrigerant system does not increase above 16 bar at ambient temperatures lower than 25 degrees C (the coolant fan runs and cools the condenser).
- Via the duty cycle (Read Measuring Value Block, display group "001", display field "3") the A/C Control Head -E87- calculates the pressure in the refrigerant circuit.
- When the duty cycle is smaller than 12.5% (corresponds to approx.: 1.8 bar absolute pressure) and greater than 87.5% (corresponds to approx.: 32 bar absolute pressure) the compressor is not switched on by the A/C Control Head -E87- (A/C Compressor Regulator Valve -N280- is not activated). The compressor will be switched on again when duty cycle is greater than 12.5% (correspond 1.8 bar absolute pressure) or smaller than 48% (corresponds to 16 bar absolute pressure).
- If the pressure in the refrigerant circuit or the engine coolant temperature is too high, the A/C Control Head -E87- regulates the compressor performance (to avoid sudden compressor cut-off):
- When pressure in refrigerant circuit exceeds 30 bar (absolute pressure) (the complete compressor output is only switched again after the pressure is less than 27 bar).
- As soon as the coolant temperature reaches 115 degrees C (at 118 degrees C compressor is switched off completely).
- If the pressure in the refrigerant circuit was greater than 32 bar (duty cycle greater than 87.5%) the compressor is switched on again by the A/C control head -E87-, if pressure drops below 29 bar (duty cycle is less than 84%).
- Additional notes on pressures in the refrigerant circuit "Read Measuring Value Block", display group "001".
Identifying malfunctions at temperature increase behind condenser
- Pinch both coolant hoses from engine to heater core using hose clamps 3093 or 3094.
- Repeat A/C system cooling performance test.
- Do both measuring values in display fields "3" and "4" of display group "009" deviate less than 3 C from Evaporator Vent Temperature Sensor -G263- (display field "1" of display group "010"?
