A/C Refrigerant System, Testing
A/C Refrigerant System, Testing
Special Tools And Equipment
- Diagnostic Operation System VAS 5051 A e.g. with Diagnostic Cable - 3 Meter VAS 5051/5A and K-Lead Adapter Vas6017B VAS 6017B (or K-Lead Adapter VAS 6017A)
- Minitester V.A.G 1362 (for temperature measurement) or commercially available thermometer
Test requirements
- Ambient temperature above 15 degrees C
- Radiator and condenser clean (clean if necessary)
- Ribbed belt for compressor drive OK and correctly tensioned, pulley actually driving compressor (not for vehicles with 8- cyl. engine)
- Compressor drive unit (connection between compressor and engine) properly installed (vehicles with 8-cyl. engine only.
- All air guides, covers and seals OK and properly installed
- Airflow through dust and pollen filter not impeded by contamination
- Vehicle not exposed to sunlight
- Engine warm
- DTC memory checked, all displayed faults eliminated and DTC memory erased.
Check DTC Memory (Function 02)
Erase DTC Memory (Function 05)
- Coding checked and corrected if necessary and reading measuring value block.
Reading
- Basic setting performed.
Basic Setting (Function 04)
- All instrument panel vents open
- Hood closed
- Settings on operating and display module, Climatronic Control Module J255:
- "Auto" mode
- "LO" temperature setting (for drivers and passengers side)
- Compressor on (lamp in Econ button not lit)
- Functions with engine running (and air conditioner switched on):
- Operation of Coolant Fan V7 (speed governed by pressure in refrigerant circuit and engine temperature)
- Operation of Fresh Air Blower V2 at maximum speed
- Switching of air conditioner to recirculated-air mode (approx. 1 minute after starting vehicle, fresh-air/air flow flaps are closed and recirculated-air flap opened, air is drawn in by Fresh Air Blower V2 from passengers footwell)
NOTE: If one of these test requirements is not fulfilled, check DTC memory and perform Output Diagnostic Test Mode (DTM) diagnosis.
Check DTC Memory (Function 02)
Output Diagnostic Test Mode (DTM) (Function 03)
Checking
- Measure ambient temperature (must be above 15 degrees C).
- Close doors, hood, windows and sun roof.
- Open all instrument panel vents.
- Switch ignition on.
- Set "Econ" mode on operating and display module, Climatronic Control Module J255 (lamp in Econ button lights).
- Start engine.
- Start air conditioner On Board Diagnostic (OBD). VAS 5051A Scan Tool (ST), Connecting and Selecting Functions
- In "Reading measuring value block" function, select display group "001". Reading
- Check display in display zones:
- Display field "2" shows 0% (compressor off).
- Display field "4" indicates that pressure in refrigerant circuit at measured ambient temperature is equal to or greater than value in table.
Ambient temperature in Displayed pressure (in bar absolute)
degree C
15 4.7
20 5.6
25 6.6
30 7.6
35 8.8
NOTE:
- At absolute pressure, "0 bar" corresponds to an absolute vacuum. Normal ambient pressure thus corresponds to roughly " 1 bar" absolute. 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").
- The pressure in the refrigerant circuit is governed by ambient temperature. Due to heat emitted by components (e.g. coolant fan), the pressure displayed with warm engine is slightly higher than that indicated for the relevant ambient temperature.
- If the pressure displayed is lower than that given in the table, check measured value of High Pressure Sensor G65 "Reading measuring value block" and "Electrical checks, test step 5". If no malfunction is found at the High Pressure Sensor, there is not enough refrigerant in the circuit. Reading
If pressure in refrigerant circuit is OK:
- Switch on compressor by selecting "Auto" mode on operating and display module, Climatronic Control Module J255 (lamp in Econ button does not light).
- Set "Lo" temperature (for drivers and passengers side) on operating and display module, Climatronic Control Module J255.
- Set air outflow direction on operating and display module, Climatronic Control Module J255 to "instrument panel vents".
- In "Reading measuring value block" function, select display group "001". Reading
- Check display in display zones:
- Display field "2" shows a duty cycle of greater than 30% (activation of A/C Compressor Regulator Valve N280, compressor is switched on).
- Display field "1" shows a current of greater than 0.3 A (current flowing via A/C Compressor Regulator Valve N280, compressor is switched on).
- Displayed pressure in zone "4" rises above value when compressor is switched off.
NOTE:
- The A/C Compressor Regulator Valve N280 is activated by the operating and display module, Climatronic Control Module J255 such that the temperature of the air downstream of the evaporator reaches the specified value (approx. 2 to 5 degrees C). After starting the vehicle, a value greater than 75 % (0.55 A) is displayed depending on measured temperature, engine speed and electrical system voltage. As soon as the temperature measured by the Evaporator Vent Temperature Sensor G263 approaches the specified value, activation is cancelled and compressor output thus reduced.
- Under certain operating conditions, residual moisture in the coolant circuit may lead to the formation of ice at the compressor regulating valve. Such ice formation impairs compressor control, the evaporator is cooled excessively and ices up. Icing-up of the evaporator may give rise to the following problems:
- Repeated or sporadic failure of air conditioner (no cooling/heat output) after a long journey; air conditioner functions properly again after a short delay following engine shutoff.
- Misting up of windows on inside after a long journey; windows are initially not cleared even by pressing "Defrost" button; air conditioner functions properly again after a short delay following engine shutoff.
- Remedy:
- Check measured value of Evaporator Vent Temperature Sensor G263 "Reading measuring value block", display group "010". Reading
- If the sensor measured value is too high under usage conditions described by customer (greater than e.g. 10 degrees C although air conditioner is functioning properly), check Evaporator Vent Temperature Sensor G263 (incorrect measured value can cause evaporator to ice up).
- If the sensor measured value is too low under usage conditions described by customer (colder than 0 degrees C for lengthy period at ambient temperature above 0 degrees C) although the A/C Compressor Regulator Valve N280 is not currently being activated, the vehicle must be taken to a dealership which services A/C systems.
- Check refrigerant line between evaporator and accumulator (thick line, low-pressure end) with engine running. If this line is severely iced up when the problem occurs (a thin layer of ice is permissible), this is also an indication that the temperature in the evaporator is too low.
- Make the air conditioner workshop aware of any problem encountered. The necessary work discharging of refrigerant circuit, replacement of and subsequent evacuation of refrigerant circuit for at least 3 hours.
- If display zone "1" shows no or insufficient current, check activation of A/C Compressor Regulator Valve N280 "Electrical checks, test step 6".
- If the pressure indicated in display zone "4" does not change and compressor activation is OK (display zones "1" and "2"), there is a malfunction in the refrigerant circuit.
- Press recirculated-airflap button ("recirculated-air mode" symbol in button lights).
- Set engine speed to 2000 RPM (start of time measurement).
- In "Reading measuring value block" function. select display group "010". Reading
- Compare measured value indicated in display zone "1" (for Evaporator Vent Temperature Sensor G263) to values in graph.
A. Air temperature measured by Evaporator Vent Temperature Sensor G263
B. Ambient temperature
C. Permissible tolerance range
Depending on ambient temperature, the measured air temperature must be within the stated tolerance range after 5 minutes.
NOTE:
- If the required values are not attained, check measured value of Evaporator Vent Temperature Sensor G263. Compare measured values shown in display groups "010", zone "1" and "009", zones "3" and "4":
- If the measured value in the two display zones "3" or "4" only differs slightly from the measured value in display group "010", perform "Corrective actions if readout does not match specification".
- If the measured value of the Evaporator Vent Temperature Sensor G263 is higher than that of the Left Vent Temperature Sensor G150 and the Right Vent Temperature Sensor G151, check proper installation of Evaporator Vent Temperature Sensor G263 and perform electrical check for this sensor "Electrical checks, test step 2".
- Operation of the air conditioner can be established, for example, from cooling down of the refrigerant line on the "low- pressure end" (thick line).
If the measured value of the Evaporator Vent Temperature Sensor G263 (and thus the air conditioner cooling output) is OK:
- Compare measured value indicated in zone "1" of display group "010" (for Evaporator Vent Temperature Sensor G263) to measured values of display group "009", zones "3" and "4" ( Left Vent Temperature Sensor G150 and Right Vent Temperature Sensor G151).
After 5 minutes, the measured values in display group "009", zones "3" and "4" ( Left Vent Temperature Sensor G150 and Right Vent Temperature Sensor G151) must not be more than 3 degrees C higher than the value in zone "1" of display group "010" (for Evaporator Vent Temperature Sensor G263).
NOTE:
- If the required values are not attained, compare measured values indicated in display group "009", display zones "3" and "4":
- If the measured value in one of the two display zones "3" or "4" is OK, check the temperature flap control motor for the side on which the measured value is not OK ( Left Temperature Flap Motor V158 or Right Temperature Flap Motor V159) and perform electrical checks for Left Vent Temperature Sensor G150 and Right Vent Temperature Sensor G151 "Electrical checks, test step 2".
- If the measured value in display zones "3" or "4" of display group "009" is lower than that in display zones "1" of display group "010", check Evaporator Vent Temperature Sensor G263, Left Vent Temperature Sensor G150 and Right Vent Temperature Sensor G151 for proper installation and contact resistance at electrical connections and replace defective sensor if necessary.
- If no malfunction is found at the Left Vent Temperature Sensor G150 or the Right Vent Temperature Sensor G151 and at the Left Temperature Flap Motor V158 or the Right Temperature Flap Motor V159, perform measures to be taken in the event of temperature increase downstream of evaporator.
- The temperature of the air flow from the "Center" instrument panel vents can additionally be measured using the Minitester V.A.G 1362 (or a commercially available thermometer).
- Display group "009", display zones "1" and "2" indicates the measured value for the Left Footwell Vent Temperature Sensor G261 and the Right Footwell Vent Temperature Sensor G262. As the air flow in "Auto" mode is only routed to the instrument panel vents, these two sensors indicate an imprecise value in this setting. Pressing the "Air down" button makes it possible to incorporate these sensors into the test as well.
Identifying Malfunctions If Specified Values Are Not Obtained
- If applicable, check again that compressor is actually being driven. On vehicles with 8-cyl. engine, the drive shaft may have become removed from the compressor drive unit.
- degrees C the pressure should not exceed 20 bar. Under extreme usage conditions (e.g. in hot countries with high ambient temperatures, "stop and go traffic" and high relative humidity), the high cooling output then required may also result in pressures of up to 31 bar.
- At ambient temperatures below 25 degrees C the pressure in the refrigerant circuit does not usually rise above 16 bar ( Coolant Fan V7 run(s) and cool(s) condenser).
- The duty cycle (reading measuring value block, display group "001", display zone "3") is used by the operating and display module, Climatronic Control Module J255 to calculate the pressure in the refrigerant circuit. Reading
- If the duty cycle is less than 12.5% (corresponding to approx. 1.8 bar absolute pressure) and greater than 87.5% (corresponding to approx. 32 bar absolute pressure), the operating and display module, Climatronic Control Module J255 does not switch on the compressor (the A/C Compressor Regulator Valve N280 is not activated). The compressor is only re-activated once the duty cycle exceeds 12.5% (corresponding to absolute pressure of 1.8 bar) or drops below 48% (corresponding to absolute pressure of 16 bar).
- To prevent abrupt compressor shutoff because of excessive pressure in the refrigerant circuit or excessive coolant temperature, the compressor output is reduced by the operating and display module, Climatronic Control Module J255:
- As soon as the pressure in the refrigerant circuit exceeds 30 bar (absolute) (full compressor output is not released again until pressure has dropped below 27 bar)
- As soon as the coolant temperature exceeds 115 degrees C (full shutdown at 118 degrees C)
- If the pressure in the refrigerant circuit had been in excess of 32 bar (duty cycle greater than 87.5%), the operating and display module, Climatronic Control Module J255 does not reactivate the compressor until the pressure has dropped below 29 bar (duty cycle less than 84%).
- For further notes on pressure in refrigerant circuit, refer to "Reading measuring value block", display group "001". Reading
Identifying Malfunctions At Temperature Increase Behind Condenser
