Refrigerant Pressure Sensor / Switch: Description and Operation

NOTES:
- Check shift pressures, switch and sensor removing and installing, as well as switch locations in A/C system.
- There are several different versions of switch and sensor.


A/C pressure switch -F129-





- The compressor shuts off during a pressure drop in the A/C system (protects the compressor in an empty A/C system).
- The compressor shuts off when there is excess pressure in the A/C system.
- The coolant fan switches to second speed when pressure increases in A/C system.
- Switch functions, see below.


Valve connection for pressure switch





A/C system pressure switches use different size threads than the service connection.

Use only these O-ring seals for connections. A/C Coupler O-ring
A - Connection (lubricated)
B - O-ring seal
- Valve


Switch Functions





The high/low pressure switch (located between terminals -1- and -2-) switches the compressor off (via A/C control head -E87-) when there is excessively high or low pressure in the A/C system.

Switching pressures (in bar)
Switch open (compressor off):
- Low pressure: switch opens at 1.2 bar (17.4 psi) and closes at 1.8 bar (25.2 psi)
- High pressure: switch opens at 30 bar (420 psi) and closes at 14.5 bar (203 psi)

Switch closed (compressor on):
- 1.2 (1.8) bar to 30 (14.5) bar

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

Switching pressures (in bar):
- Fan speed 2 on (switch closes) at 16 bar (232 psi)
- Fan speed 2 off (switch opens at 12.5 bar (181 psi)