Opel 1900 1973 Service Manual page 534

Figure 95.17 Float Type Flow Valve
enough to close the valve and stop the flow of refrig-
erant liquid.
For the sake of simplicity, we have described the
float and valve action as being in a sort of definite
wide open or tight shut condition. Actually, though,
the liquid level falls rather slowly as the refrigerant
boils away. Likewise, the float goes down gradually
and gradually opens the valve just a crack. New
refrigerant liquid barely seeps in through the
"cracked" valve. At such a slow rate of flow, it
the liquid level in the evaporator very slowly.
With that in mind, it is easy to see
possible for a stabilized condition to exist. By that,
we mean a condition wherein the valve would be
ACTUATING
PINS \
t
PASSAGE
SEAT
OUTLET
Figure Thermostatic
REFRIGERANT COMPONENTS ALL MODELS
raises
would be
how it
PLATE
ORIFICE
AGE SPRING
SPRING SEAT
Expansion Valve
opened barely enough to allow just exactly the right
amount of refrigerant liquid to enter the freezer to
take the place of that leaving as a vapor.
Thermostatic Expansion Valve
Automotive air conditioning systems use a thermo-
static expansion valve in place of the float system.
Figure 9B-18 shows a cross-section of the valve
which consists primarily of the gas-filled power ele-
ment, body, actuating pins, seat and orifice. At the
high pressure liquid inlet is a tine mesh screen which
prevents dirt, tilings or other foreign matter from
entering the valve orifice.
When the valve is connected in the system, the high
pressure liquid refrigerant enters the valve through
the screen from the receiver-dehydrator (which acts
as a storage tank for the condensed refrigerant as it
leaves the condenser) and passes on to the seat and
orifice. Upon passing through the orifice the high
pressure liquid becomes low pressure liquid. The low
pressure liquid leaves the valve and flows into the
evaporator core where it absorbs heat from the
evaporator core and changes to a low pressure vapor,
and leaves the evaporator core as such. The power
element bulb is clamped to the low pressure vapor
line just beyond the outlet of the evaporator (Fig.
The operation of the valve is quite simple. It is a
matter of controlling opposing forces produced by a
spring and the refrigerant pressures. For example:
The pressure in the power element is trying to push
the seat away from the orifice, while the spring is
trying to force the seat toward the orifice. These
opposing pressures are established in the design of
the valve so that during idle
system is not operating, the spring force and the
refrigerant pressure in the cooling coil are always
Figure Expansion
periods, i.e. when the
Valve Bulb Location