Disconnect the lower solenoid valve vacuum hose from the 3-way connector and connect the vacuum pump.
Disconnect the upper solenoid valve vacuum hose from the vacuum manifold and connect a pressure gauge.
Start the engine. Create a vacuum. If the solenoid valve holds a vacuum, then see item A), if not - item B).
A) Turn on the A/C switch.
Create a vacuum.
If the pressure gauge shows a vacuum, see A1), if not - item A2).
A1) Turn off the A/C switch.
If the pressure gauge shows vacuum, the solenoid valve should be replaced.
If not, then the vacuum line should be checked for proper connection, cracks, blockage or hose disconnection.
A2) Disconnect the 2-pin connector near the solenoid valve.
Measure the voltage between Red (+) and Cherny (-) contacts on the wiring of the air conditioner.
If battery voltage is present, the solenoid valve should be replaced.
If there is no voltage, then measure the voltage between Red (+) contact and weight.
If there is battery voltage, then the gap in the Black conductor between the solenoid valve and point G15 should be repaired.
If there is no voltage, then you should inspect for a break in the Red wire between the solenoid valve and terminal 17 of the control unit. If the wire is normal, then you should refer to the diagnostics section of the inputs of the control modules.
B) Disconnect the 2-pin connector near the solenoid valve.
Measure the voltage between the Red and Black terminals of the A/C wiring harness.
If voltage is present, refer to the control module input diagnostics section.
If there is no voltage, then the solenoid valve should be replaced.