Pressures In Refrigerant Circuit, Checking (Using Service Station)

Pressures In Refrigerant Circuit, Checking (Using Service Station)

NOTE:
- Check cooling performance. A/C system is functioning correctly when a temperature of 7 degrees C or lower escapes at instrument panel air vents.
- Setting on Climatronic "LO".
- Setting on A/C system "AC" on; "max"; "cold".
- Connections with valve and service connections for measuring and testing.

Test requirements
- Radiator and condenser 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.
- Electrical system and vacuum system fault-finding has not revealed any malfunctions.
- On Board Diagnostics (OBD) of A/C system using diagnostic operation system VAS 5051A in "Guided Fault Finding" cannot detect any malfunction, no shut-off condition for A/C compressor is displayed in measuring value block (only in vehicles with "A/C system" OBD).
- 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 at normal operating temperature Vehicle not standing in direct sunlight The ambient temperature is greater than 15 degrees C.
- All instrument panel vents open.
- With engine running and A/C system set to maximum cooling performance:

Set cooling performance to maximum.

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

Setting on heater controls:
- Press A/C button and Rec- or recirculated air button.
- Turn rotary temperature control towards "Cold" stop.
- Set rotary fresh-air blower control to "4".
- Coolant Fan(s) V7 operating (at least stage 1).*

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

- Operation of Fresh Air Blower V2 at maximum speed.
- Recirculated/fresh-air flap set to "Recirculated air mode" (within 1 min. after starting vehicle, air flow flap is closed and recirculated air flap opened).*
- Coolant shutoff valve closed.*
- Valves of pump valve unit closed and no coolant circulation pump delivery.*

Pressures, checking
- Switch ignition off.
- Connect service station. Working With Service Station
- Take pressure gauge readings (two possible results).

Ambient temperature Pressure in refrigerant circuit
(in degrees Celsius) in bar positive pressure
+15 degree C 3.9
+20 degree C 4.7
+25 degree C 5.6
+30 degree C 6.7
+35 degree C 7.8
+40 degree C 9.1
+45 degree 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) equals 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 for which measured pressure is displayed in measured value block, pressure measured should coincide with values in table.

Pressure in refrigerant circuit lower than indicated in table

Not enough refrigerant in refrigerant circuit.
- Determine whether refrigerant circuit is leaking.
- Check pressure relief valve.

If pressure relief valve has responded:
- Check actuation of radiator fans.
- Check for constricted refrigerant pipe and hose cross-sections caused by inadequate bending radii.
- Check refrigerant pipes and hoses for external damage.
- If no fault 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. A/C Compressor Regulator Valve N280 is activated by Climatronic Control Module J255.

If compressor is not driven with engine running or regulating valve is not actuated:
- Establish 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, repair A/C clutch.
- Check activation of A/C Compressor Regulator Valve N280.

Continuation of pressure testing
- Checking pressures for vehicles with restrictor and reservoir (with internally regulated compressor). Restrictor and Reservoir (With Internally Regulated Compressor), Checking
- Checking pressures for vehicles with expansion valve and receiver (with internally regulated compressor). Expansion Valve and Receiver (With Internally Regulated Compressor), Checking
- Checking pressures for vehicles with expansion valve and receiver (without internally regulated compressor). Expansion Valve and Receiver (Without Internally Regulated Compressor), Checking
- Checking pressures for vehicles with restrictor, reservoir and A/C Compressor Regulator Valve N280 (externally regulated compressor). Restrictor, Reservoir and A/C Compressor Regulator Valve N280 (Externally Regulated Compressor), Checking