Chevrolet 10 Series 1967, Service Manual

Page: 46 / 605

HEATER AND AIR CONDITIONING 1A-18
3. Vehicle in NEUTRAL with engine running at 2000
rpm.
4. Air Conditioning controls set for -
• Maximum cooling.
• High blower speed.
5. TEMP knob and AIR knob set for full recirculating
air. On Comfortron systems move the control lever
to REAR and pull the white vacuum hose from the
transducer. Plug the hose. An alternate method is
to install the J-22368 Tester (described later in this
section) and operate it on MANUAL control to main­
tain maximum cooling and blower speed.
6
. Gauge set installed.
7. System settled out (run-in approximately 10 minutes).
8
. A thermometer placed in front of vehicle grille and
another in the right hand diffuser outlet.
PERFORMANCE DATA
The following Performance Data define normal opera­
tion of the system under the above conditions. Relative
humidity does not appear in the tables because after
running the prescribed length of time on recirculated air
and maximum cooling, the relative humidity of the air
passing over the evaporator core will remain at ap­
proximately 35% to 40% regardless of the ambient tem­
perature or humidity.
Should excessive head pressures be encountered at
higher ambient temperatures, an 18" fan placed in front
of the vehicle and blowing into the condenser will provide
the extra circulation of air needed to bring the pressures
to within the limits specified.
NOTE: Higher temperatures and pressures
will occur at higher ambient temperatures. In
areas of high humidity it is possible to have
thermometer and gauge readings approach but
not reach the figures listed in the performance
tables and still have a satisfactory operating
unit. However, it is important to remember that
low pressure has a direct relationship to nozzle
outlet temperature. If pressure is too low, ice
will gradually form on the evaporator fins, r e ­
stricting airflow into the passenger area and
resulting in insufficient or no cooling.
Four Season Systems
(Refrigerant Charge = 3 Lbs. - 4 Oz.)
Temperature of
Air Entering
Condenser
70° 80° 90° 100° 110°
1 2 0
°
Engine rpm
2 0 0 0
Compressor Head
Pressure
145 185 200 215 255
155 195 210 225 265
285
295
Evaporator Pressure
at STV
Dependent Upon Altitude
See Chart Under Evaporator Con­
trol Valve (POA)
Discharge Air
Temp, at Right
Hand Outlet
38 38 40 41 43
41 41 43 44 46
48
51
EVAPORATOR CONTROL VALVE (POA)
Four Season
The only check for proper POA valve operation is to
check the suction pressure at the valve as during a
performance test. The POA valve is an absolute valve
and will provide different gauge readings based on the
altitude where the readings are being taken. Correct
gauge reading at sea level is
29.5
psig. Gauge readings
will be one-half psi higher for each additional
1 0 0 0
feet
of elevation. The following table lists gauge readings at
different altitudes. If a valve gives improper gauge
readings, it must be replaced since it is not repairable
or adjustable.
29.5
psig. - - Sea Level
30 .0
psig. —
1000
ft.
30.5
psig. —
2000
ft.
3 1.0
psig. —
3000
ft.
31.5
psig. —
4000
ft.
3 2.0
psig. —
5000
ft.
3 2.5
psig. —
6000
ft.
33.0
psig. —
7000
ft.
33.5
psig. —
8000
ft.
3 4.0
psig. —
9000
ft.
34.5
psig. —
10000
ft.
EXPANSION VALVE
A malfunction of the expansion valve will be caused
by one of the following conditions: valve stuck open,
valve stuck closed, broken power element, a restricted
screen or an improperly located or installed power
element bulb. The first three conditions require valve
replacement. The last two may be corrected by replacing
the valve inlet screen and by properly installing the
power element bulb.
Attachment of the expansion valve bulb to the evapo­
rator outlet line is very critical. The bulb must be
attached tightly to the line and must make good contact
with the line along the entire length of the bulb. A loose
F ig . 28 - Evaporator Pressure Control V a lv e POA
CHEVROLET TRUCK SERVICE MANUAL