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, refer to 64 50... AIR CONDITIONER TEST (R 134A) .

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.

Fig 1: Identifying Pressure Reading (Normal Inlet Pressure And High Outlet Pressure Indicate An Overfilled System)

Courtesy of BMW OF NORTH AMERICA, INC.

Remedy:

Draw off, evacuate and refill A/C system. Refer to 64 50 009 DRAWING OFF, EVACUATING AND FILLING A/C SYSTEM (R 134A) . Clean condenser from outside, check auxiliary fan, replace if necessary.

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

Remedy:

Fig 2: Identifying Pressure Reading (High Inlet Pressure And Low Outlet Pressure Indicate A Faulty Compressor)

Courtesy of BMW OF NORTH AMERICA, INC.

Replace compressor.

Compressor does not run with equal inlet and outlet pressures.

Fig 3: Identifying Pressure Reading (Compressor Does Not Run With Equal Inlet And Outlet Pressures)

Courtesy of BMW OF NORTH AMERICA, INC.

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).

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

Fig 4: Identifying Pressure Reading (Normal Inlet Pressure And Low Outlet Pressure Indicate An Insufficient Fill Quantity Of Refrigerant)

Courtesy of BMW OF NORTH AMERICA, INC.

Remedy:

Draw off and measure refrigerant, refer to 64 50 009 DRAWING OFF, EVACUATING AND FILLING A/C SYSTEM (R 134A) .
If the amount drawn off corresponds approx. to the specified fill quantity (740+/-25 g), check expansion valve for unobstructed through flow; replace if necessary.
Then evacuate and refill A/C system, refer to 64 50 009 DRAWING OFF, EVACUATING AND FILLING A/C SYSTEM (R 134A) .

Low inlet pressure and high outlet pressure can be 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: Identifying Pressure Reading (Icing Of Evaporator)
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: Identifying Pressure Reading (Low Inlet Pressure And High Outlet Pressure Indicate An Obstruction In The Condenser Area)
Courtesy of BMW OF NORTH AMERICA, INC.