- Print. Hg - Inches of mercury vacuum
- Print. WC - Inches of Water Column
- JB - Junction Box
- KO - Knock Out
- KW - Kilowatts
- LL - Low Limit
- LP - Low Pressure or Liquified Petroleum
- LPS - Low Pressure Steam
- LRA - Locked Rotor Amps
- LWCO - Low Water Cut Off
- MA - Mixed Air
- MAT - Mixed Air Temperature
- MAU - Make-up Air Unit
- MCC - Motor Control Center
- MFD - Micro-Farad
- MP - Motor Protector
- MPT - Male Pipe Thread
- NC - Normally Closed
- NEC - National Electric Code
- NFPA - National Fire Protection Association
- NO - Normally Open
- NPT - National Pipe Thread
- NTC - Negative Temperature Coefficient
- OA - Outside Air
- OAT - Outside Air Temperature
- OP - Oil Pressure
- ODP - Ozone Depletion Potential
- PCB - Printed Circuit Board
- PE - Pneumatic to Electric
- PID - Proportional, Integral, & Derivative
- PRV - Pressure Reducing Valve
- PSC - Permanent Split Capacitor
- PSIA - Pounds per Square Inch Absolute
- PSIG - Pounds per Square Inch Gauge
- PT - Pressure Temperature
- PTAC - Portable Terminal Air Conditioner
- PTC - Positive Temperature Coefficient
- PWM - Pulse Width Modulation
- RA - Return Air or Reverse Acting
- RAT - Return Air Temperature
- RF - Return Fan
- RH - Relative Humidity
- RPBP - Reduced Pressure Backflow Preventer (sometimes also seen as RPZ)
- RPM - Revolutions Per Minute
- RTU - Roof Top Unit
- RV - Reversing Valve
- SA - Supply Air
- SAT - Supply Air Temperature
- SD - Smoke Damper
- SEER - Seasonal Energy Efficiency Ratio
- SF - Service Factor or Supply Fan
- SH - Super Heat
- SP - Static Pressure or Set Point
- SPDT - Single Pole Double Throw
- SPST - Single Pole Single Throw
- SV - Solenoid Valve
- TD - Temperature Difference or Time Delay
- TDS - Total Dissolved Solids
- TEV - Thermostatic Expansion Valve (sometimes also seen as TXV)
- Ton - Ton of refrigeration effect
- UH - Unit Heater
- UV - Ultra-Violet or Unit Ventilator
- VAV - Variable Air Volume
- VFD - Variable Frequency Drive
- VSD - Variable Speed Drive
- VVT - Variable Volume / Temperature
- W - Watt
- WB - Wet Bulb
- WC - Water Column
- XFMR - Transformer
