1993 DODGE TRUCK check engine

24-12
HEATING
AND AIR
CONDITIONING

PERFORMANCE TEMPERATURE CHART

Garage
Ambient
Temperature
21
°C

(70°F) 26.5°C
(80°F) 32°C
(90°F) 3/.5°'J
(100T) 43°C
(110°F)

Discharge
Air Temperature
3-10°C
(38-50°F) 6-12°C
(42-54'F) 8-14°C
(46-58°F) 10-17°C
(50-62°F) 12-19°C
(54-66°F)

Compressor
Discharge Pressure
1344 a
1620 a
1861 kPag 2103 a 1379kPcg
2344 a

Compressor
Discharge Pressure

120 •
195 PS'9 160 .
235 PS'9 200 .
270 PS'9 240 .
305 PS'9 280 .
340 PS'9

Evaporator
Suction Pressure
124 kPag
207 a 138 kPag
241 J 269 kPag III kP°9
296 179 ,D
324 kPag

Evaporator
Suction Pressure

18 .
30 PS'9 20 .
35 pS'g 22
39 pS,g
25 .
43 pS'g 26 .
47 pS'9
J9124-97 pressure must drop to below -50 kPag (15 inch of vacu­

um).
If the condition is not met the H-valve is stuck
open and should be replaced. Remove Liquid C02 and
watch evaporator suction pressure; it should increase to a minimum of 262 kPag (38 psig) and then stabilize to a
pressure of 172-240 kPag (25-35 psig). Any H-valve
which does not produce this response is stuck open and should be replaced.
(4) Connect A/C water valve vacuum hose (gray)
and set temperature control in cool position.
(5) Set engine speed at 1,000 RPM and blower on

HI.
The evaporator suction pressure should be in the
range of 138-207 kPag (20-30 psig). If compressor dis­ charge is higher than 1 656 kPag (240 psig), check
for restricted discharge line, radiator overheating, air in system or faulty viscous fan drive. If discharge
pressure is less than 966 kPag (140 psig), check com­
pressor head gaskets and discharge reeds.
(6) Connect the electrical wires to the electronic
temperature cycling clutch switch.
VACUUM CONTROL SYSTEM ADJUSTMENTS
AND TESTS To keep the vacuum harness in place, common vi­
nyl tape (sometimes called plastic tape of electri­
cian's tape) cannot be used. It will cause the tube to
deteriorate directly under the tape, when high under­
hood temperatures are involved. A compatible nylon type of tape such as MS CH69 (#281) or an equiva­lent must be used.
The test of the push button switch operation deter­
mines whether or not the vacuum and electrical cir­ cuits are properly connected and the controls are
functioning properly. However, it is possible that this system operating perfectly at engine idle during high
manifold vacuum, may not function properly at high engine speeds. Before starting this test, stop engine and make certain the vacuum source hose at engine
intake manifold is tight on its connector.
EXPANSION (H) VALVE TEST
Test must be made at ambient temperature of
21°C-29°C (70°F-85°F).
After performing all previously mentioned tests,
conduct the H-valve test as follows:
(1) Operate the engine at 1,000 RPM with the win­
dows closed. Set air conditioning controls for MAX
A/C,
high blower, temperature control lever in full
reheat position and cycling clutch switch electrically
bypassed. Disconnect and plug the water valve vac­ uum hose in the engine compartment. (2) Operate the system for at least 5 minutes in or­
der to obtain partial stabilization and sufficient re­
heat to load the system. Pressure at the discharge service port should reach 966-1 656 kPag (140-240
psig) (Fig. 6). If head pressure of 966-1 656 kPag (140-240 psig) cannot be obtained, check system
charge level.

Fig.
6
Expansion
(H)
Valve
Test

WARNING:
EXTREME
CARE
MUST
BE
USED
WHEN
HANDLING
LIQUID
C02 AS
SKIN
INJURY
CAN OC­

CUR
IF
PROTECTIVE
GLOVES
ARE NOT
WORN.
(3) Put Liquid C02 on control head (completely cover
head) for a minimum of 30 seconds. Evaporator suction

•

HEATING
AND AIR
CONDITIONING
24 - 13 Start Vacuum Pump Tool
C-4289
and connect the
Vacuum Test Set Tool
C-3707.
With the prod
blocked, adjust bleed valve to obtain a vacuum read­ ing of exactly -27 kPag (8 inches of mercury) - (Fig.
7).

VACUUM PUMP

Fig.
7
Adjust
Vacuum
Test
Bleed
Valve

It is essential that the bleed valve be adjusted so
the vacuum gauge pointer will return to exactly -27 kPag (8 inches) with the prod blocked. Otherwise a
false reading will be obtained when the control cir­
cuit is tested.
Alternately release and block the hose prod several

times.
Make sure the bleed valve is adjusted so the vacuum gauge pointer returns to exactly -27 kPag (8 inches of vacuum) when the prod blocked (Fig. 7).
Disconnect engine vacuum source hose at engine
intake manifold and insert vacuum tester hose prod
into source hose leading to push button switch. Place
vacuum gauge on the cowl so it can be observed from
the driver's position as push buttons are operated.
Start the test by depressing the control HEAT
mode button. Vacuum tester gauge needle will drop
until the actuator has operated. It should then return
to -25 to -27 kPag
(7-1/4
to 8 inches) depending on
vacuum leakage. Continue to depress; OFF, MAX.

A/C,
A/C,
VENT,
DEFROST
and
HEAT
mode but­

tons.
Allowing time for actuators to operate after each button is pushed and for the vacuum to stabi­

lize.
Note the vacuum drop below -27 kPag (8 inches)
after each operation. The maximum allowable vac­
uum drop below -27 kPag (8 inches) after each oper­ ation is -3 kPag (3/4 inch). (Bypass the vacuum
storage tank if so equipped).
If the vacuum drop is more than -3 kPag (3/4 inch),
first recheck the tester for reading exactly -27 kPag
(8
inches). If correct, inspect the fit of the 7 port hose
connector plug on the push button switch. This plug
must be positioned all the way onto the 7 ports on
the push button switch.
CAUTION:
Do not use
lubricant
on the
switch ports
or
in the
holes
in the
plug,
as
lubricant
will
damage
the vacuum valve
in the
switch.
If it is
difficult
to
properly position connector plug
on the
switch
ports,
put a
drop
or two of
clean
water
in the
con­

nector plug holes. This
will
allow
the
plug
to
slide
completely
on the
switch ports.

If vacuum drop is now within limits, proceed with
the over-all performance test. If vacuum drop is still in excess of
-3
kPag (3/4 inch), remove 7 port connec­
tor from switch and seal port No. 6 with a finger to check source hose. Then remove prod from source
line and insert it alternately into each connector port
except No. 6 (Fig. 8).

Fig.
8
Vacuum
Tube
Assembly
Test
Note amount of vacuum drop below -27 kPag (8
inches) after each actuator has operated. If vacuum
test gauge comes back to -27 kPag (8 inches) at each of the 7 ports, the hoses and actuators are not leak­
ing. The control switch is faulty and must be re­
placed. If excessive vacuum drop shows up at one or
more ports in connector block, isolate faulty hose or actuator.
Inspect hose connections to the actuator involved.
Then test whether actuator or hose is at fault; use
the test hose on the actuator involved (Fig. 9).
A leak in a hose may be detected with vacuum test
set by running the fingers along the hose and watch­
ing vacuum gauge reading. The tube can be repaired
by cutting out the "leak" and inserting the tube ends into a 3 mm (1/8 inch) inside diameter rubber tube.
Wet the tube with water to aid assembly.
A vacuum drop in excess of 3 kPag (3/4 inch) below

-27
kPag (8 inches) will not interfere with engine op­
eration. A rough idle may occur. It can, however, in-

24 - 14
HEATING
AND AIR
CONDITIONING

•

Fig.
9
Vacuum
Actuator Test terfere with the proper operation of the air
conditioning and heating controls at high speeds and
during acceleration.
COMPRESSOR NOISE Noises that develop during air conditioning opera­
tion can often be misleading.
FOR EXAMPLE: What sounds like a failed front
bearing or connecting rod, may be caused by loose

bolts,
nuts, mounting brackets or a loose clutch as­ sembly.
Improper belt tension is also often the source of an
objectionable noise and can easily be mistaken for in­
ternal compressor troubles.
Drive belts are speed sensitive. That is, at different
engine speeds, and depending upon belt tension, belts
can develop unusual noises that are often mistaken
for mechanical problems within the compressor.
The adjustment procedures follows: (1) Select a quiet area for testing. Switch compres­
sor on and off several times to clearly identify com­
pressor noise. (2) Tighten all compressor mounting bolts, clutch
mounting bolt, clutch coil mounting screws and com­
pressor drive belts. Check that plumbing is not rub­
bing other parts. (3) Make sure that matched drive belts are in
equal tension. Replace any parts that are defective or
missing.
(4) Test the vehicle. If noise persists, continue
trouble shooting system for source of noise. Refer to A/C Compressor and Clutch Diagnosis
Charts.

CLUTCH COIL
TEST
(1) Verify battery state of charge (test indicator
should be green.)
(2) Connect an ammeter (0-10 ampere scale) in se­
ries with the clutch coil terminal. Use a voltmeter (0-20 volt scale) with clip leads measuring voltage
across the battery and A/C clutch.
(3) With A/C control in A/C mode and blower at
low speed, start the engine and run at normal idle.
(4) The A/C clutch should engage in 11 seconds af­
ter the start. The clutch voltage should be within 2
volts of the battery voltage. If the A/C clutch does not engage, check the fuse.
(5) The A/C coil is acceptable, if the current draw
is 2.0 to 3.7 amperes at 11.5 to 12.5 volts. The test
room temperature should be 18°C to 24°C (65°F to
75°F).
Where voltage is more than 12.5 volts, add
electrical loads as needed by increasing blower speed
and/or switching other electrical accessories on. If
coil current reads zero, the coil is open and should be
replaced. If the ammeter reading is 4 amperes or more, the coil is shorted and should be replaced. If
the coil voltage is not within 2 volts of the battery
voltage, check the circuit external to the clutch coil for excessive voltage drop and repair accordingly.
Refer to A/C Compressor and Clutch Diagnosis
Charts.

HEATING
AND AIR
CONDITIONING
24 -
A/C COMPRESSOR AND CLUTCH DIAGNOSIS

A/C
COMPRESSOR NOISY

?

COMPRESSOR
OFF
COMPRESSOR
ON

I

CLUTCH PULLEY
RUBBING
EVALUATE INSIDE
VEHICLE MODE- MAX
A/C

BLOWER-LOW
OUTLETS-OPEN WINDOWS-
CLOSED

EVALUATE INSIDE
VEHICLE MODE- MAX
A/C

BLOWER-LOW
OUTLETS-OPEN WINDOWS-
CLOSED

CLUTCH BEARING NOISY
MOUNTING

BOLTS
LOOSE
TIGHTEN

•

REMOVE
BELTS

RECHECK
RUBBING AND BEARING
NOISE
LOOSE

BELTS

ADJUST

*
»

CHECK
AIR
GAP
RESET
IF
NOT

0.406
-
0.787
mm (0.016-0.031 In)
BELT
INTERFERENCE

• I

BENT PULLEY

REPLACE
PULLEY AND
ARMATURE KNOCKING
OR

GRINDING NOISE
FROM

COMPRESSOR

_ *

DEFECTIVE COIL IF
SO

REPLACE REPLACE

COMPRESSOR



FRONT
ALIGNMENT PIN LOOSE
OR
OUT
OF

SPECIFICATION
REPLACE

COMPRESSOR
FRONT

COVER
COMPRESSOR
WONT
TURN

PROPERLY
CLUTCH ENGAGES BUT SLIPS
OR
SMOKES
CLUTCH SLIPPING LOW VOLTAGE AT CLUTCH

CHECK
WIRING,

SWITCHES,
CLUTCH
AMPERAGE
AND
GROUND

I

AMPERAGE

GREATER
THAN
5
AMPS
CLUTCH COIL PARTIALLY SHORTED

REPLACE
COIL

OIL/GREASE
ON

FRICTION
SURFACES

CHECK
SHAFT
SEAL
FELT

COIL SNAP RING
NOT
PROPERLY

INSTALLED
IF BEARING DEFECTIVE
REPLACE

PULLEY
AND
ARMATURE NOTE: APPLY PARKING
BRAKE
AND RUN
ENGINE
IN
NEUTRAL ONLY.

*
CLUTCH OR BELT SUPPING CAN BE
CAUSED
BY OVERCHARGED
SYSTEM
OR CONDENSER FAN
NOT
RUNNING. OIL SATURATED

FELT
REPLACE
COMPRESSOR
SHAFT SEAL ADJUST BELT
TENSION

REPLACE
IF

NECESSARY
CLUTCH
PULLEY RUBS ON COIL
COIL
MISMOUNTED

SEIZED

COMPRESSOR

T

REPLACE

COMPRESSOR

AND CLUTCH
ASSEMBLY

GREASE
PURGED
FROM
BEARING
REPLACE
CLUTCH
PULLEY
AND
ARMATURE

GREASE
PURGED

FROM
BEARING
REPLACE
CLUTCH
PULLEY
AND
ARMATURE

J9324-99

24 - 16 HEATING AND AIR CONDITIONING

A/C
COMPRESSOR AND CLUTCH DIAGNOSIS (CONT.)

COMPRESSOR
CLUTCH
WON'T
ENGAGE

f
f

NO
VOLTAGE
VOLTAGE
AT
AT CLUTCH CLUTCH
NORMAL

f t
OPEN FUSE FAULTY

GROUND

f
1
PUSHBUTTON SWITCH OPEN COIL
f
FAULTY

WIRING
REPLACE
COIL
f
r

POOR
VOLTAGE
AT

GROUND CLUTCH LOW

f

CHECK
WIRING

AND SWITCHES

f

CHECK
VOLTAGE
DROPS
FROM

CLUTCH TOWARD BATTERY
CYCLING SWITCH IF CONTACT OPEN

CHECK

REFRIGERANT
CHARGE

IF CHARGE
OK REPLACE SWITCH
COMPRESSOR
LEAKS
OIL OR REFRIGERANT
DEFECTIVE
CRANKSHAFT
SEAL

CARTRIDGE
DEFECTIVE
CRANKSHAFT
SEAL

PLATE

DEFECTIVE

SEAL
("O' RING),
FRONT
COVER,
REAR
COVER
DEFECTIVE

COMPRESSOR
THRU
BOLT

READ

COMPRESSOR

SERVICE
SECTION FOR REPAIR
DEFECTIVE

COMPRESSOR
BODY

REPLACE

COMPRESSOR

NOTE: APPLY PARKING BRAKE
AND RUN ENGINE
IN
NEUTRAL
ONLY.

24
- 20
HEATING
AND AIR
CONDITIONING

• (3) Turn
3
refrigerant manifold valves completely
clockwise
to
puncture
the
cans
and
close
the
mani­
fold valves.
(4) Purge
the air
from
the
charging line
by
loosen­
ing
the
charging hose
at the
manifold gauge
set and

turn
one of the
refrigerant valves counterclockwise. When
the
refrigerant
gas
starts escaping from
the

loose connection, tighten
the
hose.
(5) Fully open
all 3
refrigerant manifold valves
and place
the
cans
of
refrigerant into
a pan
contain­
ing 52°C (125°F) water.
The
water will warm
the

charging
can and aid in the
transfer
of the
charge
into
the
system.
(6) Start
the
engine
and
move
the
controls
to A/C

low blower position.
The electronic temperature cycling switch will pre­
vent
the
clutch from engaging until refrigerant
is
added
to the
system.
If the
clutch does engage,
re­

place
the
switch before proceeding
any
further. (7) Charge through
the
suction side
of the
system
by slowly opening
the
suction manifold valve. Adjust
the valve
as
necessary
so
charging pressure does
not
exceed
345
kPag
(50
psig). Maintain
the
temperature
of
the
water
in the pan by
adding warm water
as

necessary. (8) Adjust
the
engine speed
to a
fast idle
of
approx­
imately
1,300 RPM.
(9) When
all 3
cans
of
refrigerant
are
completely
empty, close
the
manifold gauge
set
valves
and re­

frigerant manifold valves. The maximum refrigerant charge
is 44 oz.

REFRIGERANT
LEAK REPAIR PROCEDURE

LOST CHARGE If
the
system
has
lost
all
charge
due to a
leak: (1) Evacuate
the
system.
(2) Charge
the
system with approximately
1
pound
of refrigerant. (3) Locate
all
leaks.
(4) Repair
all
leaks.
(5) Replace filter-drier bottle.

CAUTION:
Replacement
filter-drier
units
must
be

sealed
while
in
storage.
The
drier
used
in
these

units
absorbs
and
traps
moisture
quickly
upon
ex­

posure
to the
atmosphere.
When
installing
a
drier,

have
all
tools
and
supplies ready
for
quick
reas­

sembly
to
avoid keeping
the
system open
any
longer
than
necessary.

(6) Check system
oil
level. (7) Evacuate
and
charge
the
system.
LOW CHARGE If
the
system
has not
lost
all of its
refrigerant
charge; locate
and
repair
all
leaks.
If it is
necessary
to increase
the
system pressure
to
find
the
leak
(be­
cause
of an
especially
low
charge),
add 230 g (1/2 lb)

of refrigerant.
If
there
has
been
a
significant
oil
loss,
check
the
system
oil
level.
If
leak repair
was
possible
without discharging system
and an oil
level check
was
not
necessary,
use
procedure
for
correcting
low

refrigerant level.

CORRECTING
LOW
REFRIGERANT LEVEL
Since
the
refrigeration system
is
completely sealed,
the refrigerant level will
not be low
unless there
is a
leak
in the
system. Before adding refrigerant where
the
cause
of a low

level
is not
known,
the
system should
be
tested
for

leaks.
Assuming that leaks have been corrected without
discharging
the
system, proceed with partial charge.
Install
and
connect manifold gauge
set.
(1) Close both manifold gauge
set
valves. Open
manifold gauge
set
needle valve.
(2) Connect
the
suction gauge test hose
to the
suc­
tion service port
of the
compressor. Connect
the
dis­ charge gauge test hose
to the
discharge service port. (3) Connect
an end of
long test hose
to the
center
manifold outlet,
and
other
end to
refrigerant dispens­ ing manifold. (4) Close
the 2
dispensing manifold valves
and

open remaining dispensing manifold valve. Remove
protective
cap
from opened valve.

WARNING: NEVER
USE
THESE CANS
TO
CHARGE
INTO
THE
HIGH
PRESSURE SIDE
OF
THE
SYSTEM

(COMPRESSOR
DISCHARGE
PORT)
OR
INTO
A
SYSTEM
THAT
IS AT
HIGH
TEMPERATURE.
THE
HIGH
SYSTEM PRESSURES COULD
BE
TRANS­
FERRED
INTO
THE
CHARGING
CAN
CAUSING
IT

TO EXPLODE.

(5) Screw
a can of R-12 to the
opened manifold
valve.
Be
sure gasket
is in
place
and in
good condi­
tion. Tighten refrigerant
can and
manifold locking nut
to
ensure
a
good seal.
Do not
overtighten.
Tighten
to 9.5 N*m (7 ft. lbs.)
torque,
if
gasket
is in
good condition.
(6) Turn manifold valve (above
the
refrigerant
can)

completely clockwise
to
puncture
the can.
This closes
the valve
and
seals
the
refrigerant
in the can.

CAUTION:
Do not
heat refrigerant
12
above
52°C

(125°F).

(7) Place refrigerant
can in a
large
pan of
water
heated
to
52°C (125°F). Place
pan of
water containing
the refrigerant
can on an
accurate scale
so the
amount
of
refrigerant added
can be
weighed. Open
the refrigerant manifold valve.
(8) Purge
all air
from test hoses.
Air in the
system
will
be
trapped
in the
condenser causing abnormally
high discharge pressures
and
interfering with con­ densing
of the
refrigerant.

•

HEATING
AND AIR
CONDITIONING
24 - 21 (a) Loosen both test hoses at the manifold gauge
set. Tighten the hoses as soon as the air is purged. (b) Loosen charging hose connection at manifold
gauge set. This will purge air from the charging

hose.
Tighten connection as soon as air is purged.
(9) With vehicle windows open and hood up, oper­
ate engine at 1,300 RPM. (10) Place air conditioner control on A/C and place
the fan switch on high. (11) If necessary, block the condenser to maintain
a discharge pressure of 1 550-1 725 kPag (225-250

psig).
System must be charged through the evapora­
tor suction service ports as follows:
(a) Slowly open the suction service gauge valve.
Meter flow of refrigerant by adjusting the suction service gauge valve so the pressure registered at
the suction service gauge does not exceed 345 kPag

COMPRESSOR
J
(50
psig). Keep refrigerant container upright.
(b) Add refrigerant gas until there is no foam visi­
ble at the sight glass. As soon as all foam clears, note the weight registered on the refrigerant scale.
(c) Watch the refrigerant weighing scale and add
437 g (14 oz.) of refrigerant (equivalent to 1 can).
(d) Close the suction gauge valve.

CAUTION:
TOO
much
refrigerant
in the
system
can

cause
abnormally high discharge pressures. Care
must
be
used
so the
exact recommended amount
of
refrigerant
is
added
after
foam clears
in the
sight

glass.

(e) Close dispensing manifold valve. Remove test
hoses and adapters from the service ports of com­
pressor and install protective caps at service ports.

RVICE (SD-709)

INDEX

page

Compressor
21

Compressor
Shaft Seal
.................... 25
The A/C system uses a 7 piston design Sanden SD-
709 compressor. Designated the SD-709, the compres­
sor is mounted on the front right side of the engine
and is driven by a serpentine belt.
System lubrication is provided by 135cc ±15cc (4.6
cu. in. ±0.5 cu. in.) of 500 viscosity refrigerant oil.
The clutch used on the compressor consists of 3 ba­
sic components:
(1) The pulley.
(2) The front plate. (3) The field coil.
The pulley and field coil are attached to the front
head of the compressor with snap rings. The hub is keyed to the compressor shaft and is retained on the
shaft with a self-locking nut. Special service tools are
required to remove and install the clutch plate on
the compressor shaft.

COMPRESSOR
REMOVAL
(1) Disconnect the negative cable from the battery.
(2) Disconnect the clutch lead wire.
(3) Remove the discharge and inlet (suction) ser­
vice valves from the compressor. Plug or tape all the
openings.
(4) Refer to Group 7, Cooling System and remove
the drive belt(s). (5) Remove the bolts and lift the compressor from
the mounting bracket (Fig. 1).
page

Cylinder Head
/
Valve Plate
27
Magnetic
Clutch
22

Fig.
1
Compressor
Mounting

INSTALLATION
If a replacement compressor is being installed,
check the oil level. Add or subtract oil as necessary.
Install the magnetic clutch on the compressor.
(1) Install the compressor on the mounting bracket.
Tighten the bolts to 27 N*m (20 ft. lbs.) torque.
(2) Refer to Group 7, Cooling System and install
the drive belt(s).
(3) Check the belt tension.
@ New drive belt-800-900 N (180-200 lbs-f).
• Used belt-623-712 N (140-160 lbs-f).

24 - 30
HEATING
AND AIR
CONDITIONING

•
up,
down or to either side and can be shut off by
pushing the vanes up. Floor air is delivered through
the lower outlets.

VACUUM CONTROLS
AND
CIRCUITS
For an explanation of the vacuum and electrical
logic that controls the operation of the unit (Fig. 1
and Control Chart). MODES—The vacuum and electrical logic is deter­
mined by the push button switch. The vacuum por­
tion of the switch controls the water valve and
positions all doors in the unit except the blend air
door. The electrical portion of the switch controls the compressor and blower operation. The following is a
breakdown of the vacuum and electrical logic for each mode. Refer to Control Chart in this section.
OFF Vacuum application is as indicated in Fig. 1. The
inlet air door is closed to outside, open to recirculat­
ing air. The mode door is in the A/C position. The
Heat/Defrost door is in the Heat position. The heater core coolant flow is
shut-off.

No air flows through the unit and the compressor
is idle because the blower and compressor clutch cir­
cuits are open.
MAX A/C All of the doors are in the same position as they
are in Off. The Max. A/C mode merely closes the
electrical circuits to the blower motor and the com­
pressor clutch. This mode is recommended for initial cool down, extreme outside humidity or high ambient
temperature.

A/C
This mode is recommended for use after the vehicle
has been cooled to the desired temperature. The vac­
uum application at the outside-recirculating air door actuator is transferred to the rod side. This moves
the door away from the outside-air inlet and closes
the recirculating inlet. The water valve is open. All
other vacuum applications and door positions are the
same for the Max. A/C position. The blower motor and compressor are on.
VENT The vacuum circuit remains the same as in the
A/C position but the compressor clutch electrical cir­
cuit is opened, preventing the compressor from oper­ ating. The blower motor is used to force outside air
into the passenger compartment through the A/C
outlets in the instrument panel.

HEAT
In the Heat mode the outside air door is open same
as A/C mode. Vacuum is applied to the top side of the air condi­
tioning door actuator. This will close off the passage
to the air conditioning distribution duct and open the
passage to the heater/defroster duct. Since the heat­ er-defroster door is in the heat position, the full flow
of heated air goes through the heater outlets. A
small amount of heated air will bleed through the
defroster outlets. The water valve is open, the blower
switch is activated and the compressor is off.
DEFROST When the defrost mode is selected all conditions
are the same as for heater operation, except that no
vacuum is applied to the defrost door actuator. The defrost door is spring loaded to the defrost position.
The door opens the defroster outlets and partially closes off the heater outlets. The heater outlets are
left open far enough to direct about 30 percent of the
air to the floor. The other 70% is defrost air directed
to the windshield area. The compressor clutch will be engaged.

ELECTRICAL CONTROLS AND CIRCUITS
The electrical feed for the air conditioning circuit is
from 2 fuses in the fuse block. A 20 ampere fuse pro­
tects the compressor clutch circuit, and a 30 ampere fuse protects the blower motor control circuit.

CONTROL TEST
Test operation of controls in the following manner.
(1) Inspect compressor drive belt. Adjust, if neces­
sary. (2) Start engine. (3) Move temperature lever to extreme left (cool)
position. (4) Push A/C button.

(5)
Refer to Control Chart. Check position of doors,
operation of compressor clutch, blower motor and wa­
ter valve. The water valve is open when there is no
vacuum to valve. (6) Check blower switch by moving it to all 4 posi­
tions and noting air flow change. In case of malfunc­
tion refer to Electrical Control Circuit. (7) Check operation of blend air door by moving
temperature lever from full warm toward cool posi­
tion. Discharge air temperature should change with lever movement if the engine coolant is warm. (8) Repeat steps 5 and 6 in each push-button posi­
tion. If actuation of the doors is slow or incomplete,
check for mechanical misalignment, binding or vac­ uum leaks. The air conditioning door has a seven
second vacuum delay in mode switching from Off,
Max A/C, A/C, or Vent to Heat or Defrost. Check
temperature control cable for correct adjustment.