Most of the service work performed in air conditioning requires the use of a set of two gauges, one for the high (discharge) pressure side of the system, the other for the low (suction) side.
The low side gauge records both pressure and vacuum. Vacuum readings are calibrated from 0 to no less than 30 in. Hg (0–206 kPa) and the pressure graduations read from 0 to no less than 60 in. Hg (413 kPa).
The high side gauge measures pressure from 0 to at least 600 in. Hg (0–4137 kPa). Both gauges are threaded into a manifold that contains two hand shut off valves. Proper manipulation of these valves and the use of the attached test hoses allow the user to perform the following services:
The manifold valves are designed so they have no direct effect on gauge readings, but serve only to provide for, or cut off, flow of refrigerant through the manifold. During all testing and hook-up operations, the valves are kept in a closed position to avoid disturbing the refrigeration system.