Buick LeSabre 1965 Service Manual page 777

11 - 4 4 OPTIONAL HEATER-AIR CONDITIONER SYSTEM
ACCESSORIES
VACUUM
DIAPHRAGM
SCHRADER
VALVE
CONNECTOR-
O-RING
LIQUID
BLEED CONNECTOR
EQUALIZER LINE
OPENING
FROM
EVAPORATOR
OUTLET
ASSIST
SPRING
LOCK NUT
SCREEN
PISTON
DIAPHRAGM
TO COMPRESSOR
SUCTION
Figure 11-52-Suction Throttling Valve - 45000, 46000 and 48000 Series
is obtained when 4-1/2 inches of
vacuum is applied to the STV vac-
uum diaphragm. The internal
spring in the diaphragm is com-
pressed, thus the spring in the
cover is the only controlling fac-
tor. When at the maximum cool-
ing position, evaporator pressure
is allowed to go to a minimum of
29-31 psi. If pressure is allowed
to go lower, icing of the evapora-
tor will occur.
(d) Minimum cooling setting of
the 45000, 46000 and 48000 STV.
The minimum cooling setting is
obtained when vacuum is not ap-
plied to the vacuum diaphragm.
The diaphragm spring tension is
added to the tension of the spring
in the cover. The evaporator
pressure then must overcome
both springs to move the piston.
The evaporator pressure will be
maintained at approximately 32
to 34 psi.
NOTE: At 60 mph it will not be
unusual for the compressor inlet
pressure to be from 10 to 15 psi,
while the evaporator is controlled
at 30 psi. Frost accumulates on
the compressor inlet line after
prolonged operation at these con-
ditions. At minimum, or further
reduced-load conditions, when the
throttling demands on the STV
are again increased, the com-
pressor inlet pressure may drop
to zero psi, or even 6
M
— 8
M
of
vacuum. Compressor inlet tem-
peratures at these reduced load
conditions may approach minus
30° F. so that even frosting of the
c o m p r e s s o r rear head is
possible.
8. Vacuum Modulator - 49000.
The vacuum modulator which con-
trols the amount of vacuum to the
49000 suction throttle valve vacu-
um diaphragm, is mounted on the
air conditioner control assembly
on the center console. It is acti-
vated by the air conditioner tem-
perature control lever and the
FAN switch control lever.
Engine intake manifold vacuum is
present at the vacuum modulator
when the air conditioner control
system is energized. The vacuum
modulator controls the output
vacuum to the suction throttling
valve from 6-7 inches vacuum at
minimum cooling, to 0 inches
vacuum at maximum cooling.
When air conditioner temperature
control lever is moved from left
to right, the vacuum is gradually
decreased from 6-7 inches to a
minimum of 2 1/2 inches when the