Lektro-Vend Combo Series, Service Manual

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REFRIGERATION SYSTEM THEORY OF OPERATION
REFRIGERATION PRINCIPLES
A refrigeration system is principally involved in the process of transferring heat. Heat is removed from the
vended-product area of the cabinet, and is transferred to the condenser, where it is dissipated. With vending
equipment, large quantities of heat must be transferred economically, efficiently, and repeatedly in a
continuous fashion, without loss of refrigerant gas, over a long period of time. The most common type of
refrigeration system in vending is the vapor-compression (or simple-compression) cycle system. This system
consists primarily of three elements: A compressor, an evaporator, and a condenser, joined together as a
sealed system.
In the vapor-compression system, there are two pressures present: Low (evaporating) pressure and high
(condensing) pressure. The refrigerant gas acts as the transport medium in which heat is transferred from
the evaporator to the condenser, where heat is dissipated into ambient air. A change of state occurs as the
refrigerant changes from liquid to vapor and back to liquid again, allowing the refrigerant to absorb and
discharge large quantities of heat in an efficient manner.
The basic vapor-compression cycle occurs as follows: in the evaporator, the refrigerant boils (evaporates
to vapor) at a temperature sufficiently low enough to absorb heat from the cabinet space being cooled. The
boiling temperature is controlled by the pressure maintained in the evaporator (the higher the pressure, the
higherthe boiling point). The compressor removes vapor,
via
suction lines, from the evaporator, as it is formed,
at a rate sufficiently rapid enough to help maintain the desired pressure, The compressor takes the
pressure vapor and compresses it, increasing both the pressure and temperature of the vapor. This hot
pressure gas is forced out of the compressor discharge valve and into the condenser. Upon reaching the
condenser, the refrigerant dissipates its heat and condenses into a liquid. This liquid, in turn, flows from the
condenser back to the evaporator, to repeat the cycle.