64 50... Troubleshooting by pressure measurement (R 134a)

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NOTE: The troubleshooting by pressure measurement described in the following is only possible on A/C systems with uncontrolled compressors.

This includes among others:

E53
E46M47 up to 09/2001
E38 up to 09/1997
E36, E36/7
E34
E32
E31

Connect service station to car and open both valves on the charging hoses. Adjust A/C system at control panel as described for A/C efficiency measurement.

NOTE: The following values apply as normal pressure ranges for ambient temperatures between + 20°C and + 40°C:

Inlet pressure: 1.0 - 2.2 bar
Outlet pressure: 12 - 22 bar

Normal inlet pressure and high outlet pressure indicate an overfilled system, a contaminated condenser or a faulty auxiliary fan.

Remedy:

Draw off, evacuate and refill A/C system. Clean condenser from outside, check auxiliary fan, replace if necessary.

Fig 1: Checking Auxiliary Fan

Courtesy of BMW OF NORTH AMERICA, INC.

High inlet pressure and low outlet pressure indicate a faulty compressor.

Remedy:

Replace compressor.

Fig 2: Identifying Compressor

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Compressor does not run with equal inlet and outlet pressures.

Remedy:

If the anti-icing facility has shut down the compressor, check evaporator sensor and power supply to clutch. Otherwise check clutch mechanically (by slipping).

Fig 3: Checking Evaporator Sensor & Power Supply To Clutch

Courtesy of BMW OF NORTH AMERICA, INC.

Normal inlet pressure and low outlet pressure indicate an insufficient fill quantity of refrigerant.

Remedy:

Draw off and measure refrigerant.
If the amount drawn off corresponds approx. to the specified fill quantity, check expansion valve for unobstructed through-flow; replace if necessary.
Then evacuate and refill A/C system.

Fig 4: Checking Expansion Valve
Courtesy of BMW OF NORTH AMERICA, INC.

Low inlet pressure and high outlet pressure can be caused by a variety of factors:

Icing of evaporator
Remedy: Check evaporator sensor, replace if necessary.
Obstruction on H.P. side after condenser or on L.P. side
Remedy:

Check drier, expansion valve and pipes in these areas for unobstructed through-flow; clean or replace if necessary.

Fig 5: Checking Drier, Expansion Valve & Pipes
Courtesy of BMW OF NORTH AMERICA, INC.

Low inlet pressure and high outlet pressure indicate an obstruction in the condenser area.

Remedy:

Check condenser for unobstructed through-flow; clean or replace if necessary.

Fig 6: Checking Condenser For Unobstructed Through-Flow

Courtesy of BMW OF NORTH AMERICA, INC.