Refrigerant Pressure Sensor / Switch: Description and Operation

A/C Pressure Switch -F129-, Switch Functions







The high/low pressure switch (located between terminals -1- and -2-) disengages A/C clutch -N25- (via A/C control head -E87-) when there are excessively high or low refrigerant system pressures.

Switching pressures (in bar)

Switch open (A/C clutch -N25- off):
- Low pressure: switch opens at 1.2 bar and closes at 2.4 bar
- High pressure: switch opens at 32 bar and closes at 24 bar

Switch closed (compressor on):
- 1.2 (2.4) bar to 32 (24) bar

The high pressure switch (between terminals -3- and -4-) switches coolant fan(s) -V7- to speed 2.

Switching pressures (in bar):
- Fan speed 2 on (switch closes) at 16 bar
- Fan speed 2 off (switch opens) at 12.5 bar

Removing and installing







- Disconnect harness connector.
- Remove A/C pressure switch -B-.
Tightening torque: 5 Nm (44 in. lb)
- Replace O-ring seal -A- (10.8 mm x 1.8 mm).







- To test A/C cooling efficiency with switch removed, bridge terminals -1- and -2- on connector -B-.

NOTE: Refrigerant system remains closed due to Schrader valve under switch in line connection.

Checking
- Start engine.
- Switch compressor on (select AUTO mode).

If the compressor is activated:







- Disconnect harness connector -B- from switch.
- A/C Compressor will stop (low pressure switch open).
- Remove switch -A- and install harness connector -B-.
A/C Compressor will not be activated (low pressure switch open).

If the compressor is not activated:
- Disconnect harness connector -B- from switch -A- and bridge terminals -1- and -2- on harness connector -B-.

The compressor will be activated.

NOTE:
- If the compressor is activated when the terminals are connected together, refrigerant system pressure is low or system is empty (check refrigerant system pressures.
- If the compressor is not activated and the measuring value block display indicates A/C pressure switch -F129- as the cut-off condition, there is an open circuit in the wiring between A/C pressure switch -F129- and A/C control head -E87-. Trace and repair open circuit after performing electrical test.