- outside thermostat
- overall size
- overcompensating
- overcompensation
- overcompound excitation
- overcooled
- overcooling
- overdry
- Orton cones
- oscillating compressor
- oscillating flow
- oscillating meter
- oscillating neutral
- oscillating universe
- oscillating ventilator
- oscillator
- oscillatory circuit
- osmium
- osmometer
- out
- outage
- outdoor battery
- outdoor condenser
- outerorbit
- overlap
- overlap span
- overlapping
- overload conditions
- overload relay
- overload release
- overload switch
- overpotential
- overshoot
- overstress
- oversynchronous
- overtemper
- overvoltage crowbar
- overvoltage factor
- overvoltage release
- overwater
- oxidation catalyst
- oxidation stability
- oxygen atmosphere
- oxygen point
- oxygen-free
- oxyhydrogen torch
- ozonator
- ozonizer
- ozonosphere
- packaged circuit
- packing cooler
- paddle wheel
- pair
- pair emission
- paired
- pallet load
- pallet truck
- outside fin
- outside surface
- outside temperature
- outward
- overall
- overall consumption
- overall dimension
- overexcitation
- overexposure
- overfed evaporator
- overflow
- overfreezing
- overhead battery
- overhead coil
- overhead conduit
- overhead evaporator
- overhead grid
- overheat control
- overheating temperature
- overload protection
- overload protector
- overradiation
- oversaturated vapor
- overspeed
- overvoltage
- overvoltage test
- oxidation inhibitor
- oxide-coated
- oxycalcium light
- oxygen liquefaction
- oxygen liquefier
- oxygen pulldown
- oxygenous
- ozonization
- packer
- packaged boiler
- packaged cabinet
- packaged chiller
- packaging
- packet
- packing
- packing factor
- pallet handling