Checking A/C pressure switch -F129-: Checking:

If A/C clutch -N25- does not engage with A/C ON:

• Start engine.
• Using a jumper wire, briefly bridge terminal 1 (T4a/1) and terminal 2 (T4a/2) of A/C pressure switch connector.

If A/C clutch -N25- now engages, refrigerant system is discharged (empty).

• Check A/C system for leaks, repair as necessary.

• Protects refrigerant circuit from excessive pressure
• Pressure relief valve tell-tale indicates when valve has been actuated by excessive pressure (adhesive-attached plate (arrow) is pushed out). If so, repairs must be carried out by an A/C specialist.
  Fig 1: Identifying Pressure Relief Valve On Compressor

  Courtesy of VOLKSWAGEN OF AMERICA, INC.