Buick LeSabre 1965 Service Manual page 776

ACCESSORIES
OPTIONAL HEATER-AIR CONDITIONER SYSTEM 1 1 - 4 3
cooling is obtained when vacuum
is not applied to the diaphragm.
A vacuum modulator is used with
the 49000 suction throttle valve to
vary the vacuum to the diaphragm
from 0 to 6-1/2 inches and set
it at a higher setting (less cool-
ing). The greater the vacuum
present in the diaphragm (up to
6-1/2 inches) the higher the air
conditioner outlet temperature.
The suction throttle valve (STV)
controls the evaporator pressure
and in turn the evaporator air
outlet temperature. Also the STV
prevents freezing of the conden-
sation on the evaporator core
surface. The STV consists of a
valve body, piston, piston dia-
phragm, c o n t r o l spring, dia-
phragm cover, diaphragm cap and
vacuum diaphragm. See Figures
11-52 and 11-53.
The inside of the piston is hollow
and is open to the piston dia-
phragm by small holes in the end
of the piston. Located in the
lower extremity of the piston is
a fine mesh screen, held in place
by a retainer. The purpose of this
screen is to prevent any foreign
particle of any substance enter-
ing the piston and lodging in the
holes drilled in the piston wall
and possibly scoring the surface
of the body, thus interfering with
its proper operation.
The piston diaphragm retains the
piston to it by a tab on the front
side and has the cup held against
it by the spring on the rear side.
The vacuum diaphragm actuating
pin fits in the end of the cup.
The body of the vacuum dia-
phragm threads into the valve
cover and determines the amount
of spring tension on the cup. The
vacuum diaphragm is locked in
position by a locknut.
On the 49000 Series, the suction
throttling v a l v e vacuum dia-
phragm is connected to the vac-
uum modulator on the instrument
panel by a small hose. When
vacuum is present on the dia-
phragm, it is pulled toward the
piston and its pin adds to the
spring pressure on the piston
diaphragm.
The vacuum diaphragm on the
45000, 46000 and 48000 suction
throttle valve is connected to a
vacuum disc switch which is op-
erated by the WARMER lever.
The vacuum diaphragm has a
spring inside of it. See Figure
11-52. This spring adds to the
pressure of the large spring lo-
cated in the cover when vacuum
is not p r e s e n t in diaphragm.
When vacuum is applied, the vac-
uum diaphragm compresses the
spring inside it and the spring
tension is reduced on the piston
diaphragm.
The STV inlet is connected to the
evaporator outlet and its outlet
is connected to the compressor
suction port. See Figure 11-52.
The flow of the low pressure
vapor from the evaporator to the
compressor is determined and
controlled by the position of the
piston in the valve body of the
STV. The position of the piston
in the body is determined by the
balance of the forces that are
applied to the piston diaphragm.
These forces consist of the re-
frigerant vapor pressure return-
ing from the evaporator on one
side and th spring tension, plus
the force of the actuating pin on
the other side. (The actuating
pin adds or subtracts to the
spring pressure.) Movement of
the piston permits vapor to pass
around piston and then on to the
compressor inlet.
During the time that maximum
cooling is being produced, the
STV vacuum diaphragm on the
49000 does not have vacuum ap-
plied to it, while the 45000, 46000
and 48000 vacuum diaphragm has
at least 4-1/2 inches of vacuum
applied to it. The full flow of low
pressure refrigerant vapor is be-
ing returned to the compressor to
permit it to exert its full capacity
on the evaporator and produce
maximum cooling. Under most
operating conditions, STV inlet
and outlet pressures will not be
the same as there will be some
throttling to prevent evaporator
icing.
When the operator desires to
raise the temperature within the
car, the controls are changed to
apply engine vacuum to the 49000
Series STV vacuum diaphragm.
On the 45000, 46000 and 48000 the
vacuum is exhausted from the
vacuum diaphragm. This checks
or throttles the flow of the low
pressure vapor returning to the
compressor. This results in a
higher pressure to be maintained
in the evaporator assembly. The
STV outlet pressure will also in-
crease, but the differential be-
tween STV inlet and outlet will
be greater than when STV is at
maximum cooling.
(a) Maximum cooling setting of
49000 STV - The maximum cool-
ing setting of the 49000 STV is
obtained when there is no vacuum
present at its vacuum diaphragm
and the spring tension is the only
controlling factor. When at the
maximum cool position, evapora-
ting pressure is allowed to go to
a minimum of 20 to 22 psi. If
pressure is allowed to go any
lower, icing of the evaporator
core will occur.
(b) Minimum cooling setting of
49000 STV — The minimum cool-
ing setting of the 49000 STV is
obtained when 6-1/2" (±1/2") of
vacuum is applied to STV vacuum
diaphragm. To move the piston
in the STV, the evaporator pres-
sure must overcome spring ten-
sion plus the force applied by
the actuating pin to the piston
diaphragm. This f o r c e on the
piston's diaphragm maintains an
evaporator pressure of approxi-
mately 50 psi minimum.
(c) Maximum cooling setting of
the 45000, 46000 and 48000 STV.
The maximum cooling setting of
the 45000, 46000 and 48000 STV