Refrigerant Pressure Sensor / Switch: Service and Repair
A/C Refrigerant System (R-134a) Switches & Sensors, Servicing (1997 On)
A/C Pressure Switch -F129-
Functions
- Integrated low/high pressure switch -F129- (between terminals -1- and -2-) shuts off the compressor at low or excess refrigerant system pressures (signal to A/C control head -E87-).
Switching pressures (in bar)
A/C system off (compressor off):
- Low pressure: switch (opens at 1.2 bar and closes at 1.8 bar).
- High pressure: switch (opens at 30 bar and closes at 14.5 bar).
Switch closed (compressor on)
- 1.2 (1.8) bar to 30 (14.5) bar.
High pressure switch (between terminals -3- and -4-) switches coolant fan -V7- to speed 2.
Switching pressures (in bar):
- Coolant fan speed 2 on (switch closes) at 16.8 bar.
- Coolant fan speed 2 off (switch opens) at 12.7 bar.
Removing and installing
- Disconnect electrical harness connector.
- Remove pressure switch -B-
Tightening torque: 5 Nm (44 in. lb.)
Always replace O-ring -A- (10.8 mm x 1.8 mm).
NOTE:
- To allow cooling performance checking with switch removed, bridge terminals -1- and -2- of connector -B-.
- Refrigerant circuit remains closed, connection with Schrader valve.
Check switch function:
- Start engine
- Switch on A/C (operating mode "Auto" on A/C control head).
- Compressor engages:
- Disconnect electrical connector -B- from switch -A-.
- Compressor disengages (simulates open low pressure switch).
- Remove pressure switch -A- and reconnect -B-.
- Compressor remains disengaged (simulates open low pressure switch).
- Compressor does not engage:
- Remove electrical connector -B- from switch -A- and bridge terminals -1- and -2- on connector -B- (compressor should engage).
NOTE:
- If compressor engages when bridging, either the pressure in the refrigerant circuit is too low (refrigerant system empty) or the switch is malfunctioning.
- Check refrigerant system pressures.
- If compressor does not engage and pressure switch -F129- is indicated as a compressor cut-off condition (read measuring value block), Diagnose and repair open circuit in wiring between switch -F129- and -E87-, electrical testing.