2. With the ignition off, disconnect the block at the top of the pressure switch connector.
3. Start the engine, let it idle and turn on the air conditioner on the control panel.
4. Gently wipe the viewing window on top of the dehydrator unit (see fig. 8.4).
Pic. 8.4. Air conditioning dehydrator unit
A viewing window
B Pressure sensor connector
5. Connect the pressure switch block while looking through the viewing window. This connection should result in electromagnetic engagement, and when it does, liquid should come into view. Continue observing the liquid level, which should rise above the top of the sight glass until a bubble-free flow of liquid is visible.
6. If the liquid level is lower than required or there is a pressure drop in the cooling system, the pressure switch will prevent electromagnetic engagement and the air conditioning system will not work. In this case, the vehicle must be taken to a Mercedes workshop or an air conditioning specialist for inspection and filling. Do not attempt to block the pressure sensor to restore the A/C system as this could cause serious damage to the system.