Buick LeSabre 1965 Service Manual page 775

11 - 4 2 OPTIONAL HEATER-AIR CONDITIONER SYSTEM
ACCESSORIES
the compressor to reduced oil
return. Additional considerations
for having the external equalized
expansion valve are to maintain
a full evaporator during throt-
tling, and also guard against non-
condensibles entering the system,
e s p e c i a l l y through loosened
fittings.
6. Evaporator. The evaporator
core on the 45000, 46000 and
48000 Series is of plate type de-
sign and is located near the
center of the cowl in the engine
compartment. The 49000 Series
evaporator is of the tube and fin
(Series) design and is located un-
der the right side of the instru-
ment panel.
The purpose of the evaporator
core is to cool and dehumidify
the air that is flowing through it
when the system air conditioner
is in operation. High pressure
liquid refrigerant flows through
the orifice in the expansion valve
into the low pressure area of the
evaporator. This regulated flow
of refrigerant boils immediately.
Heat from the core surface is
lost thru boiling and vaporizing
of the refrigerant which is cooler
than the core, thereby cooling the
core. The air passing over the
evaporator loses its heat to the
cooler surface of the core. As
the process of heat loss from the
air to the evaporator core sur-
face is taking place, moisture
in the air condenses on the out-
side surface of the evaporator
core and is drained off.
Since Refrigerant-12 will boil at
21.7° F. below zero at atmo-
spheric p r e s s u r e (see Figure
11-51) while water freezes at 32°
F., it becomes obvious that the
temperature in the evaporator
must be controlled so that the
water collecting on the core sur-
face will not freeze in the fins of
the core and block off the air
passages. In order to control the
temperature, it is necessary to
control the amount of refrigerant
entering the core and the pres-
sure inside the evaporator.
To obtain maximum cooling, the
refrigerant must remain in the
core long enough to completely
vaporize and then superheat a
minimum of 6° F. If too much or
too little refrigerant is present in
the core, then maximum cooling
efficiency is lost. The expansion
valve in conjunction with the suc-
tion throttling valve is used to
provide this necessary refriger-
ant volume control.
An oil b l e e d line is connected
from the bottom of the evaporator
to the outlet side (compressor
suction) of the suction throttle
valve. This bleed line is con-
nected to a check valve on the
suction throttle valve. The check
valve is a special low force
spring valve core.
The bleed line is in the system as
an insurance measure to provide
increased compressor life during
times of low refrigerant charge.
During normal-charge conditions
this line is of no particular bene-
fit as the compressor runs on an
adequate oil supply. With partial-
ly depleted refrigerant charge,
oil and refrigerant mixture will
flow from the bottom tank of the
evaporator through the oil bleed
line to the compressor. This oil
flow helps to prevent oil deficien-
cies in the compressor that could
arise under these conditions.
During times of zero-change no
refrigerant will be available to
carry oil back to the compressor.
It is therefore important that
completely discharged systems be
kept to a minimum of operation,
thus preventing seizure.
The bleed line's check valve in
the STV opens at 5 psi differential
pressure between the evaporator
inlet pressure and the STV outlet
pressure. This check valve is
fully open when these two pres-
sures exceed 12 psi differential.
Below the 5 psi differential, the
check valve will be closed to pre-
vent refrigerant and oil from
flowing out the bottom of the
evaporator. This feature prevents
RtfRIOERANI M l
PRESSURE-TEMPERATURE RELATIONSHIP
The table below indicates the pressure of
Refrigerant-12 at various temperatures.
instance, a drum of Refrigerant at a tern
ature of 80°F. will have a
psi. If it is heated to 125 F.
For
per-
pressure Of 84.1
the pressure will
increase to 167.5 psi. It also can be used con-
versely to determine the temperature at which
Refrigerant-12 boils under various pressures.
For example, at a pressure of 30.1 psi,
frigerant boils at 32°F.
TEMP. (*F.) PRESSURE (PSIO) Til
-21.7 0 (atmospheric
pressure)
-20 2.4
-10 4.5
- 5 6.8
0 9.2
5 11.8
10 14.7
15 17.7
20 21.1
25 24.6
30 28.5
32 30.1
35 32.6
40 37.0
45 41.7
50 46.7
*P. (»F.) PI
55
60
65
70
75
80
85
90
95
100
105
110
115
120
125
130
140
Re-
ESSOtE(PSHJ)
52.0
57.7
63.7
70.1
76.9
84.1
91.7
99.6
108.1
116.9
126.2
136.0
146.5
157.1
167.5
179.0
204.5
Figure 11-51—Pressure and
Temperature Relationship
of Refrigerant-12
r e f r i g e r a n t cooling capacity
losses within the evaporator as
may occur When driving thru
heavy traffic when cooling de-
mands are greatest on the system
due to low rpm of the engine.
At all times when the compressor
capacity (evaporator inlet pres-
sure) exceeds the evaporator load
demands by 5 psi or greater, this
valve starts to open. It then per-
mits refrigerant and oil to flow
from the evaporator bottom tank
to the inlet of the compressor.
7. Suction Throttle Valve. Two
different suction throttle valves
are used. One for the 45000,
46000 and 48000 air conditioner
and one for the 49000 air con-
ditioner. The difference between
these two valves is the method of
controlling the setting of the valve
for less cooling.
The 45000, 46000 and 48000 has a
two position suction throttle valve
which obtains the maximum cool-
ing setting by applying vacuum to
its vacuum diaphragm. For set-
ting this valve for less cooling,
the vacuum is exhausted from the
diaphragm.
The 49000 suction throttle valve
has a vacuum diaphragm of dif-
ferent construction. Maximum