Glossary
191
pre-heat:
The heating of diesel engine glow plugs prior to
start-up. Some engines use an intake manifold heater rather
than glow plugs.
pre-trip inspection:
Checking the operation of a
refrigeration system before loading.
psi:
Pounds per square inch. A unit of pressure.
1 psi = 0.069 bar = 6.89 kPa.
psig:
Pounds per Square Inch Gauge. Pressure in pounds per
square inch as displayed by a gauge calibrated to zero when
open to the atmosphere.
receiver tank:
A refrigerant storage device included in
nearly all Thermo King units.
refrigerant:
The medium of heat transfer in a refrigeration
system which absorbs heat by evaporating at a low temperature
and releases heat by condensing at a higher temperature.
refrigerant oil:
A special oil used to lubricate compressors in
refrigeration systems.
remote evaporator:
A separate evaporator unit located in a
second or third compartment of a multi-temperature truck or
trailer unit.
return air bulkhead:
A structure (metal or plastic) mounted
in the front of a trailer and designed to prevent restriction of
return air flow to the Thermo King unit due to improper
loading. See bulkhead.
return air temperature:
The temperature of the air
returning to the evaporator. See box temperature.
rpm:
Revolutions per minute.
setpoint:
The temperature selected on a thermostat or
microprocessor controller. This is normally the desired box
temperature.
short cycling:
When a refrigeration unit cycles between the
heat and cool modes more often than normal.
sight glass:
A system component that permits visual
inspection of oil or refrigerant level and condition.
thermostat:
A device that controls unit modes of operation to
maintain a selected box temperature.
top freeze:
When the top portion of perishable cargo is
damaged by freezing temperatures discharged from the
refrigeration unit. This may occur near the front of the box
when product is placed too close to the cold, discharge air flow.