To find the high-pressure valve:
1. Locate the air conditioning compressor, which is usually located on the passenger side of the engine compartment.
2. The high-pressure valve will be located on the compressor. It is usually a small, black valve with a Schrader valve cap.
To find the low-pressure valve:
1. Locate the air conditioning evaporator, which is usually located behind the dashboard on the passenger side of the vehicle.
2. The low-pressure valve will be located on the evaporator. It is usually a larger valve than the high-pressure valve, and it may have a blue or green cap.