Glossary
| Term | Meaning |
|---|---|
| Approach temperature | Difference between refrigerant saturation temperature and leaving water temperature in a heat exchanger |
| Back-flush | Flushing a coil or PHE in the direction opposite to normal flow |
| Breakdown maintenance | Repair done after a failure |
| COP | Coefficient of performance: heat output divided by electrical input |
| Contactor | Electrically operated switch that starts motors |
| Descaling | Removing mineral scale using a mild acid solution |
| EEV / TXV | Electronic or thermostatic expansion valve; meters refrigerant into the evaporator |
| Filter-drier | Liquid line component that removes moisture and dirt |
| Floodback | Liquid refrigerant returning to the compressor |
| Hardness | Dissolved calcium and magnesium, as mg/L CaCO₃ |
| HP / LP switch | High- and low-pressure safety switches |
| Insulation resistance | Resistance between windings and earth, tested at 500 V DC |
| Non-condensables | Air or nitrogen trapped in a refrigerant circuit |
| NTC thermistor | Temperature sensor whose resistance falls as temperature rises |
| PHE | Plate heat exchanger |
| Preventive maintenance (PM) | Planned checks done before failure |
| Root cause | The first fault in a chain that led to the symptom |
| Scale | Hard mineral layer left by heated hard water |
| Service record | Written history of readings and work on a unit |
| Subcooling (SC) | Temperature below saturation of liquid leaving the condenser |
| Superheat (SH) | Temperature above saturation of vapour leaving the evaporator |
| TDS | Total dissolved solids in water, mg/L |
| Vacuum decay test | Holding a vacuum to prove a system is tight and dry |
| Voltage imbalance | Largest deviation of line voltages from their average, as a percentage |
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