Technician Handbook Air Conditioning for Collision Repair A/C Pressure Gauge A/C system pressures indicate the condition of the AC system and are important to check. The AC Pressure Gauge determines how much refrigerant is in the system. It also provides a convenient location to attach other service equipment to the system. The AC pressure gauges can be part of a Manifold Gauge Set or built into a Charging-Recovery Station. Two gauges are connected to the system; one for the low-pressure side (blue) and the other for the high-pressure side (red). A pressure test is conducted with the system ON.
Static Pressure The static pressure (system pressure with system OFF) is of value when troubleshooting. The rule of thumb is a 1:1 ratio on the gauge reading; approximately 1 psi for every 1° F of ambient temperature. Thus, on an 80° F day, the system should have approximately 80 psi static pressure. Test CAUTION For your safety, ensure each hose is connected to the correct service port in the system. On older CFC-12 systems, the two fittings may be the same size: the high-side fitting is always a smaller diameter line, and the low-side fitting is in a larger diameter line. If in doubt, consult the Vehicle Repair Manual and carefully follow the refrigerant path to confirm each fitting.
Collision Repair & Refinish Training 29