1967 CHEVROLET CAMARO low oil pressure

HEATER
AND AIR
CONDITIONING
1A-13

AIR CONDITIONING

INDEX

Page

General Description
1A-13

Four-Season System
1A-13

Controls
1A-16

Comfortron System
. 1A-18

System Components
lA-19

Controls
1A-20

Universal System
. .
1A-21

Chevy
n
All-Weather System
•
1A-21

Corvette Four-Season System
. 1A-22

General Information
. . . 1A-26

Precautions
in
Handling R-12
1A-26

Precautions
in
Handling Refrigerant Lines
1A-28

Maintaining Chemical Stability
in the

Refrigeration System
1A-28

Gauge
Set 1A-29

Charging Station
IA-29

Leak Testing
the
System
1A-29

Vacuum Pump
1A-30

Availability
of
Refrigerant-12
. . 1A-30

Compressor
Oil 1A-31

Compressor Serial Number
1A-31

Inspection
and
Periodic Service
1A-31

Pre-Delivery Inspection
1A-31

6,000 Mile Inspection
1A-32

Periodic Service
, 1A-32

Installing Gauge
Set to
Check System Operation
....
1A-32

Performance Test
1A-32

Performance Data lA-r33

Comfortron System Operational Test
1A-33

Chevrolet Comfortron Tester
1A-34

Complete System Checks
1A-35

Maintenance
and
Adjustments ......
1A-37

Evaporator Comtrol Valve (POA)
.
1A-37
Page

Thermostatic Switch
1A-37

Expansion Valve
1A-41

Engine Idle Compensator
. . .
1A-42

Evacuating
and
Charging Procedures
1A-42

Purging
the
System
1A-42

Evacuating
and
Charging
the
System
1A-43

Checking
Oil . 1A-43

Component Replacement
and
Minor Repair
1A-45

Refrigerant Line Connections
1A-45

Repair
of
Refrigerant Leaks
1A-46

Preparing System
for
Replacement
of

Component Parts
. 1A-46

Foreign Material
in the
System
.
1A-47

Condenser
.
1A-48

Receiver-Dehydrator
1A-48

Evaporator
1A-49

Expansion Valve
1A-57

Evaporator Control Valve (POA)
1A-59

Thermostatic Switch
or
Blower Switch
. .
1A-59

All Weather-Pull Cable
1A-61

Blower Assembly
1A-62

Air Inlet Valve
.
1A-64

Blower
and
Evaporator Assembly
1A-64

Air Distributor Assembly
and
Outlet Ducts ...... 1A-64

Comfortron Automatic Control Components
1A-66

Collision Procedure lA-70

Four-Season Heater Components
1A-73

Comfortron Heater Components
. . . 1A-75

Compressor
1A-76

Wiring Diagrams
1A-78

Special Tools
.
1A-84

GENERAL DESCRIPTION

Four
air
conditioning systems
are
covered
in
this

section. They are:

1.
The
Four-Season System (Chevrolet, Chevelle,

Camaro and Corvette).

2.
The Comfortron System (Chevrolet).

3.
The All Weather System (Chevy n).

4.
The Universal System (Chevrolet, Chevelle, Chevy
n,

Camaro)

Underhood components (that
is, the
compressor,
con-

denser
and
receiver-dehydrator)
are
much
the
same
in

type,
location
and
method
of
attachment
on all of
the

above systems. The six-cylinder reciprocating compres-

sor
is
bracket-mounted
to the
engine
and
belt driven

from
the
crankshaft pulley.
The
condenser
is
mounted

ahead
of the
engine cooling radiator
and the
receiver-

dehydrator
is
mounted
in
the refrigerant line downstream

of
the
condenser.
All
cooling system components
are

connected by means
of
flexible refrigerant lines.

Evaporator size
and
location differ from system
to

system
as do
methods
of
temperature control
and air

supply
and
distribution.

FOUR-SEASON SYSTEM

The Four-Season system used
in the
Chevrolet,

Chevelle, Camaro,
and
Corvette vehicles
may be
iden-

tified
by the
fact that
it
uses
an
evaporator pressure

control known
as the POA
(Pressure Operated Absolute)

suction throttling valve.
Both
the
heating
and
cooling functions
are
performed

by this system.
Air
entering
the
vehicle must pass

through
the
cooling unit (evaporator)
and
through
(or

around)
the
heating unit,
in
that order, and the system
is

thus referred to
as a
''reheat" system.

The evaporator provides maximum cooling
of the air

passing through
the
core when
the air
conditioning sys-

tem
is
calling
for
cooling.
The
control valve acts in the

system only
to
control
the
evaporator pressure
so
that

minimum possible temperature
is
achieved without core

freeze-up.
The
valve
is
preset,
has no
manual con-

trol,
is
automatically altitude compensated,
and non-

repairable.

The heater core will be hot
at
all times since no water

valve
is
present
in
the system.

System operation
is as
follows (See Figure 24 and 25):

Air, either outside
air or
recirculated
air
enters
the

system
and is
forced through
the
system by the blower.

As
the air
passes through
the
evaporator core,
it

receives maximum cooling
if
the
air
conditioning controls

are calling
for
cooling. After leaving
the
evaporator,

the
air
enters
the
Heater
and Air
Conditioner Selector

Duct Assembly where,
by
means
of
manually operated

diverter doors,
it is
caused
to
pass through
or to
bypass

the heater core
in the
proportions necessary
to
provide

the desired outlet temperature. Conditioned airflow then

enters
the
vehicle through either
the
floor distributor

duct
or the
dash outlets. Remember that the heater core

CHEVROLET CHASSIS SERVICE MANUAL

HEATER AND AIR CONDITIONING 1A-26

clockwise for medium and high blower speed, as

desired. Low blower speed is automatic during

cooling operations.

4.
"Def-Pull". This knob should be pushed fully in.

Additional Cooling Hints

1.
The center barrel outlet in the dash may be rotated

to deflect air as desired or used to act as a shut off

door.

2.
The right and left ball outlets may be rotated to

deflect air in the direction desired. Each outlet has

a shut off valve operated by a knob approximately

4 in. inboard. When the knob is horizontal, the valve

is open.

3.
There are two (2) additional outlets in the bottom of

the ducts approximately 6" inboard from the valve

knobs. A rotating cover will open these outlets to

provide cool air for the feet if desired.

4.
When first entering a very warm car, open the

windows for a few minutes until the interior of the

car has cooled off.
Heating

1.
"Air Pull-Fan". Pull this knob fully out. Rotate

the knob clockwise for low, medium or high blower

speed as desired. If just a small amount of heat is

desired, leave the fan on low or medium speed and

regulate the temperature with the "Cool In-Hot Pull"

knob.

2.
"Air Cond-Pull". This knob should normally be

pushed fully in. However, during cool, damp days

it is possible, by pulling this knob fully out, to de-

humidify the air by passing it through the evaporator

core before reheating to the desired outlet

temperature.

3.
"Cool In-Hot Pull". Pull this knob out as far as

necessary to provide the temperature desired.

4.
"Def-Pull". Pull this knob all the way out for

maximum defrosting or de-icing. When the knob is

partly out, a portion of the hot air is used for de-

frosting and the balance is discharged through the

heater outlet.

GENERAL INFORMATION

In any vocation or trade, there are established proce-

dures and practices that have been developed after many

years of experience. In addition, occupational hazards

may be present that require the observation of certain

precautions or use of special tools and equipment. Ob-

serving the procedures, practices and precautions of

servicing refrigeration equipment will greatly reduce the

possibilities of damage to the customers' equipment as

well as virtually eliminate the element of hazard to the

serviceman.

PRECAUTIONS IN HANDLING REFRIGERANT-12

Refrigerant-12 is transparent and colorless in both the

gaseous and liquid state. It has a boiling point of 21.7^

below zero and, therefore, at all normal temperatures

and pressures it will be a vapor. The vapor is heavier

than air and is noninflammable, nonexplosive, non-

poisonous (except when in contact with an open flame)

and noncorrosive (except when in contact with water).

The following precautions in handling R-12 should be

observed at all times.

• All refrigerant drums are shipped with a heavy metal

screw cap. The purpose of the cap is to protect the

valve and safety plug from damage. It is good .prac-

tice to replace the cap after each use of the drum.

• If it is ever necessary to transport or carry a drum

or can of refrigerant in a car, keep it in the luggage

compartment. Refrigerant should not be exposed to

the radiant heat from the sun for the resulting in-

crease in pressure may cause the safety plug to

release or the drum or can to burst..

• Drums or disposable cans should never be subjected

to high temperature when adding refrigerant to the

system. In most instances, heating the drum or can

is required to raise the pressure in the container

higher than the pressure in the system during the

operation. It would be unwise to place the drum on a

gas stove, radiator or use a blow torch while pre-

paring for the charging operation, for a serious ac-

cident can result. Don't depend on the safety
plug - many drums have burst when the safety plug

failed.' Remember, high pressure means that great

forces are being exerted against the walls of the

container. A bucket of warm water, not over 125°F,

or warm wet rags around the container is all the heat

that is required.

• Do not weld or steam clean on or near the system.

Welding or steam cleaning can result in a dangerous

pressure buildup in the system.

• When filling a small drum from a large one, never

fill the drum completely. Space should always be

allowed above the liquid for expansion. If the drum

were completely full and the temperature was in-

creased, hydraulic pressure with its tremendous

force would result.

• Discharging large quantities of R-12 into a room can

usually be done safely as the vapor would produce

no ill effects, however, in the event of an accidental

rapid discharge of the system it is recommended

that inhalation of large quantities of R-12 be avoided.

This caution is especially important if the area con-

tains a flame producing device such as a gas heater.

While R-12 normally is nonpoisonous, heavy con-

centrations.. of it in contact with a live flame will

produce a toxic gas. The same gas will also attack

all bright metal surfaces.

• Protection of the eyes is of vital importance! When

working around a refrigerating system, an accident

may cause liquid refrigerant to hit the face. If the

eyes are protected with goggles or glasses, no

serious damage can result. Just remember, any

R-12 liquid that you can touch or that touches you is

at least 21.7"F. below zero. The eyeballs can't take

much of this temperature. If R-12 liquid should

strike the eyeballs, here is what to do:

1.
Keep calm.

2.
Do not rub the eyes! Splash the affected area with

quantities of cold water to gradually get the tem-

perature above the freezing point. The use of min-

eral, cod liver or an antiseptic oil is important in

CHEVROLET CHASSIS SERVICE MANUAL

HEATER AND AIR CONDITIONING 1A-28

providing a protective film to reduce the possibility

of infection.

3.
As soon as possible, call or consult an eye specialist

for immediate and future treatment.

REMEMBER -

pound of cure."
"An ounce of prevention is worth a

PRECAUTIONS IN HANDLING REFRIGERANT LINES

• All metal tubing lines should be free of kinks, be-

cause of the restriction that kinks will offer to the

flow of refrigerant. The refrigeration capacity of the

entire system can be greatly reduced by a single

kink.

• The flexible hose lines should never be bent to a

radius of less than 10 times the diameter of the hose.

• The flexible hose lines should never be allowed to

come within a distance of 2-1/2" of the exhaust

manifold.

• Flexible hose lines should be inspected at least once

a year for leaks or brittleness. If found brittle or

leaking they should be replaced with new lines.

• Use only sealed lines from parts stock.

• When disconnecting any fitting in the refrigeration

system, the system must first be discharged of all

refrigerant. However, proceed very cautiously re-

gardless of gauge readings. Open very slowly, keep-

ing face and hands away so that no injury can occur

if there happens to be liquid refrigerant in the line.

If pressure is noticed when fitting is loosened, allow

it to bleed off very slowly.

CAUTION: Always wear safety goggles when

opening refrigerant lines.

• In the event any line is opened to atmosphere, it

should be immediately capped to prevent entrance

of moisture and dirt.

• The use of the proper wrenches when making con-

nections on "O" ring fittings is important. The use

of improper wrenches may damage the connection.

The opposing fitting should always be backed up with

a wrench to prevent distortion of connecting lines or

components. When connecting the flexible hose con-

nections it is important that the swagged fitting and

the flare nut, as well as the coupling to which it is

attached, be held at the same time using three dif-

ferent wrenches to prevent turning the fitting and

damaging the ground seat.

• "O" rings and seats must be in perfect condition.

The slightest burr or piece of dirt may cause a leak.

• Sealing beads on hose clamp connections must be

free of nicks and scratches to assure a perfect seal.

MAINTAINING CHEMICAL STABILITY IN THE

REFRIGERATION SYSTEM

The metal internal parts of the Chevrolet refrigeration

system and the refrigerant and oil contained in the sys-

tem are designed to remain in a state of chemical

stability as long as pure R-12 and uncontaminated re-

frigeration oil is used in the system.

However, when abnormal amounts of foreign materials,

such as dirt, air or moisture are allowed to enter the

system, the chemical stability may be upset. When ac-

celerated by heat, these contaminates may form acids
Fig.
40-^-System Contaminants

and sludge and eventually cause the breakdown of com-

ponents within, the system. In addition, contaminates may

affect the temperature-pressure relationship of R-12,

resulting in improper operating temperature and pres-

sures and decreased efficiency of the system.

The following general practices should be observed to

insure chemical stability in the system.

• Whenever it becomes necessary to disconnect a

refrigerant or gauge line, it should be immediately

capped. Capping the tubing will also prevent dirt and

foreign matter from entering.

• Tools should be kept clean and dry. This also in-

cludes the gauge set and replacement parts.

• When adding oil, the container should be exception-

ally clean and dry due to the fact that the refrigera-

tion oil in the container is as moisture-free as it is

possible to make it. Therefore, it will quickly absorb

any moisture with which it comes in contact. For

. this same reason the oil container should not be

opened until ready for use and then it should be

capped immediately after use.

• When it is necessary to open a system, have every-

thing you will need ready and handy so that as little

Fig.
41—Gauge Set

CHEVROLET CHASSIS SERVICE MANUAL

HEATER AND AIR CONDITIONING 1A-29

time as possible will be required to perform the

operation. Don't leave the system open any longer

than is necessary.

• Finally, after the operation has been completed and

the system sealed again, air and moisture should be

evacuated from the system before recharging.

GAUGE SET

The gauge set (fig. 41) is used when purging, evacua-

ting, charging or diagnosing trouble in the system. The

gauge at the left is known as the low pressure gauge.

The face is graduated into pounds of pressure and, in

the opposite direction, in inches of vacuum. This is the

gauge that should always be used in checking pressures

on the low pressure side of the system. When all parts of

the system are functioning properly the refrigerant

pressure on the low pressure side never fails below 0

pounds pressure. However, several abnormal conditions

can occur that will cause the low pressure to fall into a

partial vacuum. Therefore, a low pressure gauge is

required.

The high pressure gauge is used for checking pres-

sures on the high pressure side of the system.

The connection at the left is for attaching the low

pressure gauge line and the one at the right the high

pressure gauge line. The center connector is common to

both and is for the purpose of attaching a line for adding

refrigerant, discharging refrigerant, evacuating the sys-

tem and other uses. When not required, this line or

connection should be capped.

NOTE:
Gauge fitting connections should be in-

stalled hand tight only and the connections leak

tested before proceeding.

The hand shutoff valves on the gauge manifold do not

control the opening or closing off of pressure to the

gauges. They merely close each opening to the center

connector and to each other. During most diagnosing

and service operation, the valves must be closed. The

only occasion for opening both at the same time would be

to bypass refrigerant vapor from the high pressure to

the low pressure side of the system, or in evacuating

both sides of the system.

CHARGING STATION

The J-8393 Charging Station is a portable assembly of

a vacuum pump, refrigerant supply, gauges, valves, and

most important, a five (5) pound metering refrigerant

charging cylinder. The use of a charging ey'inder elim-

inates the need for scales, hot water pails, etc.

The chief advantage of this unit is savings. A very

definite savings in refrigerant and time can be obtained

by using this unit. Since the refrigerant is metered into

the system by volume, the correct amount may be added

to.
the system and charged to the customer. This, coupled

with the fact that the unit remains "plumbed" at all times

and thus eliminates loss of refrigerant in purging of

lines and hooking-up, combines to enable the operator to

get full use of all refrigerant purchased by the

dealership.

All evacuation and charging equipment is hooked to-

gether in a compact portable unit (fig. 42) which brings

air conditioning service down to the basic problem of

hooking on two hoses, and manipulating clearly labeled

valves.
Fig.
42—System Charging Station

This will tend to insure that the job will be done without

skipping operations. As a result, you can expect to save

time and get higher quality work, less chance of an over

or undercharge, or comeback.

The pump mount is such that the dealer may use his

own vacuum pump. The gauges and manifold are in com-

mon use. Thus a current air conditioning dealer can use

the equipment on hand and avoid duplication.

LEAK TESTING THE SYSTEM

Whenever a refrigerant leak is suspected in the system

or a service operation performed which results in dis-

turbing lines or connections, it is advisable to test for

leaks.
Common sense should be the governing factor in

performing any leak test, since the necessity and extent

of any such test will, in general, depend upon the nature

of the complaint and the type of service performed on

the system. It is better to test and be sure, if in doubt,

than to risk the possibility of having to do the job over

again.

NOTE:
The use of a leak detecting dye within

the system is not recommended because of the

following reasons:

1.
Refrigerant leakage can exist without any oil leakage.

In this case the dye will not indicate the leak, how-

ever, a torch detector will.

2.
The addition of additives, other than inhibitors, may

alter the stability of the refrigeration system and

cause malfunctions.

3.
Dye type leak detectors which are insoluble form a

curdle which can block the inlet screen of the ex-

pansion valve.

CHEVROLET CHASSIS SERVICE MANUAL

HEATER AND AIR CONDITIONING 1A-30

Leak Detector

Tool J-6084 (fig. 43) is a propane gas-burning torch

which is used to locate a leak in any part of the system.

Refrigerant gas drawn into the sampling tube attached to

the torch will cause the torch flame to change color in

proportion to the size of the leak. Propane gas fuel

cylinders used with the torch are readily available

commercially throughout the country.

CAUTION: Do not use lighted detector in any

place where combustible or explosive gases,

dusts or vapors may be present;

Operating Detector

1.
Open control valve only until a low hiss of gas is

heard, then light gas at opening in chimney.

2.
Adjust flame until desired volume is obtained. This

is most satisfactory when blue flame is approxi-

mately 3/8" above reactor plate. The reaction plate

will quickly heat to a cherry red.

3.
Explore for leaks by moving the end of the sampling

hose around possible leak points in the system. Do

not pinch or kink hose.

NOTE: Since R-12 is heavier than air, it is

good practice to place open end of sampling tube

immediately below point being tested, partic-

ularly in cases of small leaks.

CAUTION: Do not breathe the fumes that are

produced by the burning of R-12 gas in the de-

tector flame, since such fumes can be toxic in

large concentrations of R?»12.

4.
Watch for color changes. The color of the flame

which passes through the reaction plate will change

to yellow when sampling hose draws in very small

CHIMNEY

REACTION PLATE

BURNER HEAD

Fig.
43—Leak Detector
leaks of R-12. Large leaks will be indicated by a

change in color to a vivid purplish-blue. When the

sampling hose passes the leak, the flame will clear

to an almost colorless pale-blue again. If the flame

remains yellow when unit is removed from leak,

insufficient air is being drawn in or the reaction

plate is dirty.

NOTE: A refrigerant leak in the high pressure

side of the system may be more easily detected

when, if possible, the system is in operation. A

leak on the low pressure side may be most

easily detected after the engine has been shut

off for several minutes to allow system pres-

sures to equalize. This particularly applies to

the front seal.

VACUUM PUMP

A vacuum pump should be used for evacuating air and

moisture from the air conditioning system.

Vacuum pump, Tool J-5428, (fig.. 44) is available for

this purpose. It is used as a component part of the

Charging Station J-8393, described previously. The fol-

lowing precautions should be observed relative to tbe

operation and maintenance of this pump.

' • Make sure dust cap on discharge outlet of vacuum

pump is removed before operating.

• Keep all openings capped when not in use to avoid

moisture being drawn into the system.

• Oil should be changed after every 250 hours of nor-

mal operation.

To change oil, simply unscrew hex nut located on

back side of pump, tilt backward and drain out oil

(fig. 44). Recharge with 8 ounces of vacuum pump

oil.
If you desire to flush out the pump, use this

same type clean oil. Do not use solvent.

NOTE: Improper lubrication will shorten the

life of pump.

• If this pump is subjected to extreme or prolonged

cold, allow it to remain indoors until oil has reached

approximate room temperature. Failure to warm oil

will result in a blown fuse.

• A five ampere time delay cartridge fuse has been

installed in the common line to protect the windings

of the compressor. The fuse will blow if an ex-

cessive load is placed on the pump. In the event the

fuse is blown, replace with a five ampere time delay

fuse - do not use a substitute fuse as it will result in

damage to the starting windings.

• If the pump is being utilized to evacuate a burnt-out

system, a filter must be connected to the intake

fitting to prevent any sludge from contaminating the

working parts, which will result in malfunction of the

pump.

• Do not use the vacuum pump as an air compressor.

AVAILABILITY OF REFRIGERANT-12

Refrigerant-12 is available through Parts Stock in 25

lb.
drums and in 15 oz. disposable cans. Valves are

available for
the"
disposable cans, which may be used as

individual cans or as a group of up to four cans (fig. 45).

Tool J-6272 is used with one through four cans. The

use of the four-can fixture makes it possible to charge

the system with a known quantity of refrigerant without

CHEVROLET CHASSIS SERVICE MANUAL

HEATER AND AIR CONDITIONING 1A-32

5.
Check hose clamp connections. If clamp screw torque

is less than 10 lb. in., retighten to 20-25 lb. in. Do

not tighten to new hose specifications or hose leak-

age may occur.

6. If there is evidence of an oil leak, check the com-

pressor to see that the oil charge is satisfactory.

7.
Check the system controls for proper operation.

6000 MILE INSPECTION

1.
Check unit for any indication of a refrigerant leak.

2.
If there is an indication of an oil leak, check the

compressor proper oil charge.

3.
Check sight glass for proper charge of Refrigerant-

12.

4.
Tighten the compressor brace and support bolts and

check the belt tension.

5.
Check hose clamp connections as in step 5 above.

6. Check thermostatic switch setting (Universal and

All-Weather Systems.)

PERIODIC SERVICE

• Inspect condenser regularly to be sure that it is not

plugged with leaves or other foreign material.

Fig.
46—Compressor Connector Block—Typical
• Check evaporator drain tubes regularly for dirt or

restrictions.

• At least once a year, check the system for proper

refrigerant charge and the flexible hoses for brittle-

ness,
wear or leaks.

• Every 6000 miles check sight glass for low refriger-

ant level.

• Check belt tension regularly.

• Every week - during winter months or other periods

when the system is not being operated regularly- run

the system, set for maximum cooling, for 10 or 15

minutes to insure proper lubrication of seals and

moving parts.

INSTALLING GAUGE SET TO CHECK

SYSTEM OPERATION

Compressor Suction and Discharge Connector

Compressor connector assemblies used on all vehicles

are of the same basic design consisting of the inlet

(suction) and outlet (discharge) connections, gauge fittings

and muffler and, in general, the assemblies differ only in

the location of the gauge fittings.

On Universal and Four-Season Systems the outlet line

extends along side of and toward the front of the com-

pressor and the muffler in the line is bracket mounted to

the compressor body. In all Universal Systems the gauge

fittings for both low and high pressure sides of the sys-

tem are located in the connector body. On Four-Season

Systems the high pressure gauge fitting is located on the

muffler and the low pressure gauge fitting is on the POA

Valve.

The Chevy n All-Weather System compressor con-

nector assembly is similar to the Universal System

connector assembly described above except that the

muffler extends straight out from the connector and

is not bracket mounted to the compressor.

Universal and Chevy II All-Weather System

1.
Install Gauge Adapter (J-5420 or J-9459) onto the

high and low pressure hoses of the gauge set.

2.
With the engine stopped, remove the caps from the

cored valve gauge, connectors on the compressor

fittings block.

3.
Connect the gauge lines with adapters to the threaded

connectors on the compressor fittings block.

Four-Season and Comfortron Systems

Installation of the gauge set onto the Four-Season and

Comfortron systems is accomplished in the same manner

as outlined above except that system performance checks

must be performed with the low pressure hose line and

adapter attached to the fitting on the POA valve. Charging

procedures should be performed with the high pressure

gauge line connected to the high pressure gauge fitting

located on the outlet line muffler and the low pressure

gauge line attached to the POA fitting.

CAUTION: When removing gauge lines from

the compressor fittings block be sure to remove

the adapters from the fittings rather than the

gauge lines from the adapters.

PERFORMANCE TEST

This test may be conducted to determine if the system

is performing in a satisfactory manner and should be

used as a guide by the serviceman in diagnosing trouble

CHEVROLET CHASSIS SERVICE MANUAL

HEATER AND AIR CONDITIONING 1A-37

VACUUM SYSTEM COMPONENT FUNCTION

Component

Air Door Diaphragm

Power Servo

Vacuum Relay Valve

Mode Door Diaphragm

Defroster Diaphragm

Transducer

Thermo Vacuum Valve
Vacuum Applied

Air Door Open to Outside Air

(Closed to Car Body)

Maximum Heat

Vacuum Applied to One Port Opens a Passage

Through the Valve to Allow Transducer Vacuum

to be Supplied to the Power Servo

Vacuum to Linkage Side

Air Flow Out Heater

Ducts

Full Airflow Out Heater

Outlet
Vacuum to Covered Side

Airflow Out of Upper

Outlets

Full Airflow Out Defroster

Outlets (Full De-ice)
No Vacuum Applied

Air Door Open to

Re circulated Air

(Open to Car Body)

Maximum Cooling

No Vacuum Applied Closes

Vacuum Supply to Power

Servo

Airflow Out of Upper and

Lower Outlets Door Open

1"
from 100% Lower Out-

let Position

Airflow Divided 1/3 Out

Defroster Outlets 2/3

Out Heater Outlets

Supplies Modulated Vacuum to Power Servo

Zero Voltage Applied to Transducer

Results in Maximum Vacuum Supply
10 Volts Applied to Transducer

Results in No Vacuum Supply

(Coolant Hot) Passes Vacuum When System is Calling For Outside Air

MAINTENANCE AND ADJUSTMENTS

EVAPORATOR CONTROL VALVE (POA)

(Chevrolet, Chevelle, Comoro, and Corvette

Four Season) (Chevrolet Comfortron)

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 1000 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

30.0

30.5

31.0

31.5

32.0

32.5

33.0

33.5

34.0

34.5
psig.

psig.

psig.

psig.

psig.

psig.

psig.

psig.

psig.

psig.

psig.
— Sea 1

— 1000

— 2000

— 3000

— 4000

— 5000

— 6000

— 7000

— 8000

— 9000
Level

ft.

ft.

ft.

ft.

ft.

ft.

ft.

ft.

ft.

— 10000 ft.
THERMOSTATIC SWITCH

(Universal and Chevy II All-Weather System)

Thermostatic switches used in Universal and All-

Weather systems differ only in the capillary tube sensing

unit.

The Chevy n All-Weather System thermostatic switch

has an air sensing capillary which is coiled and attached

to the front of the evaporator core with plastic plugs.

This type of unit is controlled by the temperature of the

air leaving the evaporator.

Universal systems make use of a thermostatic switch

with a fin sensing capillary or a self-supporting air sens-

ing capillary. This capillary controls the switch by

sensing the temperature of the metal fins or the air

leaving the fins.

Checking for Proper Operation

1.
Install the gauge set and set up the vehicle as

described under Performance Test.

2.
Movement of the temperature control knob should

result in a definite change in suction pressure and

cycling of the compressor clutch.

• If compressor continues to operate regardless of

the knob adjustment, it indicates that the points

CHEVROLET CHASSIS SERVICE MANUAL

HEATER
AND AIR
CONDITIONING
1A-41

OUTLET

1

TO EXPANSION
^

VALVE
TO
OIL

BLEED LINE

^ INLET

Fig.
51—Evaporator Pressure Control Valve—POA

turn increments until
the
suction pressure rises
to

the correct pressure.

5.
If the
pressure
is
more than
it
should
be,
turn the

adjusting screw counter-clockwise until
the
proper

pressure
is
reached.

6. After adjusting
the
switch, install the capillary to
its

normal position
and
observe
the
operation
of the

system
for
several minutes. Then
if
the operation
is

satisfactory remove the gauge
set,
replace the switch

and reinstall the face plate onto the evaporator case.

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
evap-

orator 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
bulb will result
in
high
low
side pressures and poor

cooling.
On
bulbs located outside
the
evaporator case

insulation must be properly installed.

The external equalizer line shown
in
Figure
55 is
not

used
in the
Custom
and
Chevy
II
All-Weather systems.

Indications
of
expansion valve trouble provided by the

Performance Test are
as
follows:

VALVE STUCK OPEN
OR
BROKEN POWER

ELEMENT

Noisy Compressor.
•

No Cooling
-
Freeze
Up.

VALVE STUCK CLOSED
OR
PLUGGED SCREEN

Very Low Suction Pressure.

No Cooling.

Fig.
52-P.O.A. Valve Installed
Fig.
53—Thermostatic Switch Removal

CHEVROLET CHASSIS SERVICE MANUAL