condenser (4). In the condenser, the high-pressure
vapor condenses to a liquid under high pressure and
gives up heat to the condenser. The heat is removed
from the condenser by the cooling medium of air or
water. The condensed liquid refrigerant is then forced
into the liquid receiver (5) and through the liquid line
to the expansion valve by pressure created by the
compressor, making a complete cycle.
Although the receiver is indicated as part of the
refrigeration system in figure 6-14, it is not a vital
component. However, the omission of the receiver
requires exactly the proper amount of refrigerant in the
system. The refrigerant charge in systems without
receivers is to be considered critical, as any variations
in quantity affects the operating efficiency of the unit.
The refrigeration cycle of any refrigeration system
must be clearly understood by a mechanic before
repairing the system. Knowing how a refrigerant
works makes it easier to detect faults in a refrigeration
The refrigeration system consists of four basic
components - t h e compressor, the condenser, the
liquid receiver, the evaporator, and the control devices.
These components are essential for any system to
operate on the principles previously discussed.
Information on these components is described in the
Refrigeration compressors have but one
purposeto withdraw the heat-laden refrigerant vapor
from the evaporator and compress the gas to a pressure
that will liquefy in the condenser. The designs of
compressors vary, depending upon the application and
type of refrigerant.
There are three types of
compressors classified according to the principle of
operation reciprocating, rotary, and centrifugal.
You may recall that material on compressors was
presented in chapter 6, Utilitiesman Basic, volume 1.
They will not be explained further here except to
discuss the special methods used to seal compressors
to prevent escape of refrigerant. Many refrigerator
compressors have components besides those normally
found on compressors, such as unloaders, oil pumps,
mufflers, and so on. These devices are too complicated
to explain here. Before repairing any compressor,
check the manufacturer's manual for an explanation of
their operation, adjustment, and repair.
EXTERNAL DRIVE COMPRESSOR.An
external drive or open-type compressor is bolted
together. Its crankshaft extends through the crankcase
and is driven by a flywheel (pulley) and belt, or it can
be driven directly by an electric motor. A leakproof
seal must be maintained where the crankshaft extends
out of the crankcase of an open-type compressor. The
seal must be designed to hold the pressure developed
inside of the compressor. It must prevent refrigerant
and oil from leaking out and prevent air and moisture
from entering the compressor. Two types of seals are
usedthe stationary bellows seal and the rotating
An internal stationary crankshaft seal shown in
figure 6-15 consists of a corrugated thin brass tube
(seal bellows) fastened to a bronze ring (seal guide) at
one end and to the flange plate at the other. The flange
plate is bolted to the crankcase with a gasket between
the two units. A spring presses the seal guide mounted
on the other end of the bellows against a seal ring
positioned against the shoulder of the crankshaft. As
the pressure builds up in the crankcase, the bellows
tend to lengthen, causing additional force to press the
seal guide against the seal ring. Oil from the crankcase
lubricates the surfaces of the seal guide and seal ring.
This forms a gastight sea whether the compressor is
operating or idle.
Figure 6-15.An internal stationary bellows crankshaft seal.