- unbalanced line
- unbalanced output
- uncondensed vapour
- undamaged frequency
- undamping
- undecomposable
- under excitation
- undercharge
- underconcentration
- undercooled
- undercooling region
- undercooling zone
- undercurrent relay
- underfill
- underfloor ventilation
- underfreezing
- underground distribution
- undercharging
- undercool
- undercooling procedure
- undercooling section
- undercritical
- underestimate
- underfloor heating
- undervoltage release
- undisturbed
- undulatory
- unearthed
- unearthed system
- unexcited
- unexposed
- unfiltered air
- unfrozen food
- unfrozen product
- unidentified
- unified
- uniflow compressor
- uniform convection
- uniform cooling
- uniform dehydration
- uniform line
- uninsulated
- underground refrigeration
- underroof ventilation
- undervoltage
- underwater acoustics
- undissolving
- undotted index
- unexpected
- unflammability test
- unfrozen equivalent
- unfrozen solution
- unfrozen state
- unidirectional microphone
- uniflow cooling
- uninterrupted duty
- uniplanar
- unit capacitor
- unit condenser
- unit length
- unit testing
- unitarity
- uniform convergence
- uniform freezing
- uniform thawing
- uniformly frozen
- unijunction transistor
- unique value
- unit pulse
- unit step
- unit time
- unity coupling
- univariant system
- universal
- universal attraction
- universal diode
- universal joint
- universal motor
- universality hypothesis
- unliquefied
- unloaded compressor
- unloading system
- unmanned
- unipolar transistor
- unit cooler
- unit fee
- unoccupied
- unorganized
- unpaired
- unrefrigerated container
- unsulated roof
- unsuperheated vapour
- untuned
- unloading cycle
- unponderable
- unrefrigerated
- unsaturated air
- unsaturated steam
- untreated air
- upfeed evaporator