Refrigerant Circuit, Checking Pressures (Using Service Station)

Refrigerant Circuit, Checking Pressures (Using Service Station)

NOTE:
- Check cooling performance. The air conditioning system is functioning correctly when the air flowing from the instrument panel vents has a temperature of 7 degrees C or lower.
- Setting on Climatronic "LO".
- Setting on air conditioning system "AC" on; "max"; "cold".
- Connections with valve and service connections for measuring and checking.

Test requirements
- Radiator and condenser are clean (clean if necessary)
- Thermal insulation at expansion valve OK and properly installed.
- Ribbed belt is OK and properly tensioned. Ribbed belt for A/C compressor and generator are OK and correctly tensioned.
- All air ducts, covers and seals OK and properly installed
- Fault finding on the electrical equipment and vacuum system found no malfunction.
- The air conditioning system On Board Diagnostic cannot determine malfunctions with the Vehicle Diagnosis, Testing and Information System VAS 5051A via "Guided Fault Finding". No shut-off condition for the A/C compressor is shown in the measured value block (only on vehicles with On Board Diagnostic "Air Conditioning System").
- Air flow through dust and pollen filter not obstructed by dirt.
- Air conditioner unit not drawing in secondary air at maximum fresh-air blower speed- Evaporator and heater not drawing in secondary air at maximum fresh-air blower speed.
- Air flaps in air conditioner unit, heater and evaporator reach end position.
- Fresh-air intake ducts beneath hood and in passenger compartment as well as corresponding water drain valves OK.
- Engine is warm
- Vehicle not exposed to direct sunlight
- Ambient temperature greater than 15 degrees C
- All instrument panel vents open
- With engine running and maximum cooling output set on air conditioning system:

Set maximum cooling output.
Setting on A/C Display Control Head E87.
- Preselect "Auto" mode (A/C compressor on).
- Set temperature selection "LO" for drivers and passengers side.

Setting on heater controls:
- A/C button and Rec- or recirculated air button pressed.
- Temperature rotary switch in "Cold" stop.
- Rotary fresh-air blower control in "4" position.

- The Coolant Fan V7 runs (the fans run) (at least in level 1)*.

NOTE: For some versions, fan is switched on only once the pressure in refrigerant circuit has exceeded a specified value.

- The Fresh Air Blower V2 runs at maximum speed.
- Recirculated/fresh-air flap set to "air recirculation mode" (within 1 min. after starting vehicle, air-flow flap is closed and recirculated air flap opened)*.
- Is the coolant shut-off valve closed.
- Are valves on pump valve unit closed and no coolant circulation pump delivery*

Pressures, checking
- Switch off ignition.
- Connecting service station.
- Take pressure gauge readings (two possible results).

Ambient temperature (in
degrees Celsius) Pressure in refrigerant circuit in bar positive pressure
+15 degrees C 3.9
+20 degrees C 47
+25 degrees C 5.6
+30 degrees C 67
+35 degrees C 7.8
+40 degrees C 9.1
+45 degrees C 10.5

NOTE:
- Temperature of refrigerant circuit components should be equal to ambient temperature.
- Pressure will deviate from values in table if individual components of refrigerant circuit are warmer or colder.
- At absolute pressure, 0 bar corresponds to absolute vacuum. Normal ambient pressure (positive pressure) corresponds to 1 bar absolute pressure. 0 pressure corresponds to an absolute pressure of one bar on most pressure gauges (indicated by -1 bar below 0).
- On vehicles with High Pressure Sensor G65 with which the measured pressure is displayed in the measured value block, the measured pressure should correspond to the values in the table.

Pressure in refrigerant circuit lower than indicated in table
Not enough refrigerant in refrigerant circuit
- Determine refrigerant circuit leaks. [1][2]Component Tests and General Diagnostics
- Check pressure relief valve.

If pressure relief valve has responded:
- Check actuation of coolant fans.
- Check refrigerant lines and hoses for cross-section constrictions caused by inadequate bending radii.
- Check refrigerant pipes and hoses for external damage.
- If no malfunction is found, flush refrigerant circuit with compressed air and nitrogen.

Pressure in refrigerant circuit in line with table or higher
- Start engine.
- Set air conditioning system to maximum cooling output.

NOTE: If the low pressure switch was removed to connect the service station, bridge the electrical connections in the corresponding connector for the pressure measurement.

- A/C compressor is driven by the engine via A/C Clutch N25.
- The A/C Compressor Regulator Valve N280 is activated by the Climatronic Control Module J255.

If compressor is not driven with engine running or regulating valve is not actuated:
- Determine and eliminate cause e.g. by checking air conditioner DTC memory.
- Observe test conditions.
- Check voltage supply for A/C Clutch N25, if this is OK, service A/C clutch.
- Check actuation of A/C Compressor Regulator Valve N280.

Continuation of checking pressures
- Check on vehicles with restrictor and reservoir (with internally regulated A/C compressor). [1][2]Component Tests and General Diagnostics
- Check on vehicles with expansion valve and reservoir (with internally regulated A/C compressor). With Expansion Valve and Reservoir (With Internally Regulated A/C Compressor), Checking
- On vehicles with expansion valve and reservoir (without regulated A/C compressor). With Expansion Valve and Reservoir (Without Regulated A/C Compressor), Checking
- Checking pressures for vehicles with restrictor, reservoir and A/C Compressor Regulator Valve N280 (externally regulated A/C compressor). With Restrictor, Reservoir and A/C Compressor Regulator Valve N280 (Externally Regulated Compressor), Checking