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A manifold gauge set reads low-side (suction) pressure and high-side (discharge/liquid) pressure. Many gauges include PT scales for specific refrigerants. Correct hose connection and valve handling prevents contamination, venting, and safety incidents.
Basics: • Blue = low side (suction service port) • Red = high side (liquid/discharge service port) • Yellow = service/charging/recovery line (to vacuum pump, recovery machine, cylinder) • Low side = lower pressure; high side = higher pressure
Common exam safety: • Never open high-side valve into suction side on a running system (can force high pressure into low side) • Use recovery equipment (EPA 608 compliance); do not vent refrigerant • Verify refrigerant type; wrong PT scale = wrong conclusions
Worked example (reading): Low side reads 68 psig on R-410A (example only). Convert to Tsat with correct scale/PT chart; then compare to line temp to compute superheat.
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