1. When the engine is not warm, disconnect the upper hose from the throttle opener.
2. Connect the vacuum pump and pressure gauge to the line through a tee.
3. Start the engine and check the vacuum in the line.
4. If the coolant temperature is above 15°C, there must be a vacuum in the system, and vice versa - there should be no vacuum at a temperature below this.
5. If vacuum measurements are not within specification, inspect for blockage of vacuum hoses. If all hoses are in order, replace thermal valve A.