HP Switch & Refrigerant Head Audit
Always distinguish between a **”Hard Trip”** (true mechanical overpressure) and a **”Nuisance Trip”** (switch failure). A true overpressure event will be accompanied by high discharge temperatures, a screaming compressor, or a dirty condenser coil. A nuisance trip occurs when the switch opens even while gauges show normal pressures.
System Protection Topography
HP switches are located on the high-side (discharge) line between the compressor and the condenser coil. They are “Normally Closed” (NC) devices that open when a bellows mechanism is expanded by excessive refrigerant force.
| Condition | Gauge Pressure | Switch Continuity |
|---|---|---|
| Safe Operation | < 400 PSI | Closed (0 Ω) |
| Safety Trip | > 500 PSI | Open (OL) |
| Switch Failure | < 300 PSI | Open (OL) – Drifted/False |
Diagnostic Gateway Challenge
A system is locked out on a high-pressure error. You measure the system pressure at 280 PSI and use your meter to check the HP switch terminals, finding an “Open” reading. What is the diagnosis?