Refrigerant Pressure Sensor / Switch: Testing and Inspection

A/C Pressure Switch -F129-, Checking







- The pressure switch can be removed without discharging refrigerant system.
- Visually check that O-ring 10.8 mm x 1.8 mm is positioned correctly in the groove.

Function

Switch part between terminals 1 and 2 switches off the A/C clutch -N25- when the system pressure is too high or when there is not enough refrigerant in the system
- Switch opens when the pressure is below 1.2 bar and closes again above 2.4 bar (switch point).
- Switch opens above 32 bar and closes again below 24 bar (switch point).

Switch part between terminals 3 and 4 switches coolant fan -V7- (via the coolant fan control module -J293-) to the next higher fan speed when system pressures increase.
- Switch closes above 16 bar and opens again below 12.5 bar (switch point).

Checking:







- With the engine running, briefly bridge terminal 1 and 2 of connector. If the A/C clutch -N25- engages, the refrigerant circuit is empty.

-F129- functional checks

To determine proper A/C system performance, perform the following functional checks with the switch installed and connected.
- Check refrigerant capacity (fill). If system pressure is too low (refrigerant leakage), -F129- switches A/C clutch off.
- Check cooling fan function. When system pressure increases, -F129- causes coolant fan -V7- to switch to next higher fan speed.
- Check if A/C system switches off. At excessive system pressures (e.g.: caused by high ambient temperatures or if condensor is blocked), -F129- switches A/C clutch off.