GMC 1976 ZEO 6083 Maintenance Manual page 46

AIR CONDITIONING SYSTEM 1- 2 9
AIR CONDITIONING SYSTEM (INCLUDES HEATING)
GENERAL DESCRIPTION
Both the heating and cooling functions are per-
formed 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" sys-
tem.
have two-way action . The whole outlet can be swiv-
eled and the inside louvers can be turned to direct air
as desired. Also there are two floor outlets.
THEORY OF OPERATION
The evaporator provides maximum cooling of
the air passing through the core when the air condi-
tioning system is calling for cooling. A thermostatic
switch, located in the blower-evaporator case, acts to
control compressor operation by sensing the fin tem-
perature of the evaporator core .
System operation is as follows : 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 As-
sembly where, by means of 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 air then enters the
vehicle through the dash outlets . When, during cool-
ing operations, the air is cooled by the evaporator to
below comfort level, it is then warmed by the heater
to the desired temperature. During "heating only"
operations, the compressor will not be in operation
and ambient air will be warmed to the desired level
in the same manner.
The dash outlets are rectangular in design and
HEAT
We all know what air conditioning does for use
but very few understand how or why it works . An air
conditioner is functionally very similar to a refrigera-
tor. A refrigerator is a simple mechanism which,
surprisingly enough, works quite a bit like a teakettle
boiling on a stove. That may sound far-fetched, but
there is more similarity between the two than most
of us would suspect. A modern refrigerator can make
ice cubes and keep food cool and fresh only because
a liquid called the refrigerant boils inside the freezer.
Everyone knows a boiling teakettle is "hot" and
a refrigerator is "cold" . We usually think of "cold"
as a definite, positive condition. The only way we can
define it is in a rather negative sort of way by saying
"cold" is simply the lack of heat, just as darkness is
the lack of light. We can't make things cold directly .
All we can do is remove some of the heat they con-
tain and they will become cold as a result . And that
is the main job of any refrigerator . Both are simply
devices for removing heat .
Transfer of Heat
The only thing that will attract heat is a colder
object . Like water, which always flows downhill,
Contents of this section are listed below:
SUBJECT PAGE N0 .
General Description . ... . . ... . . ... . . .. . . . .. . . ... . .... . . .. . .... . ... . ... . . ... . ... . . . . . . . ... . . ... . . . . . . . ... . . ... . . .. . . . .. . . ... . . ... . .. . . ... 1-29
System Components and Their Function ... . .. . . .. . . . . . . . .. . . .... . ... . . . .. . . ... . . ... . . . .. . . ... . . ... . . ... . . .. . . . .. . . .. . . .. . 1-37
General Information .. . . ... . .... . ... . . . . . . . .. . . ... . . ... . ... . ... . . ... . ... . . ... . . .. . . . .. . . .... . . .. . . . .. . . .... . . .. . . . .. . . ... . . .. . . .. . . .. . 1-51
Inspection and Periodic Service . . . . . ... . .... . ... . .... ... . . ... . .... . ... . . .. . . . .. . . .... . . .. . . . .. . . .... . . .. . . ... . . .. . . . .. . . .. . . .. . 1-56
Evacuting and Charging Procedures . . ... . . .. . . ... . ... . ... . . ... . . .. . . . . . . . ... . . . .. . . . . . . . ... . . ... . . . . . . . .. . . ... . . ... . ... . ... 1-57
Refrigerant Quick Check Procedure... . ... . . . . . . ... . ... . . .. . . ... . . .. . . . .. . . .... . . .. . . . . . . . ... . . ... . . . .. . . .. . . .... . ... . .... ... 1-61
Maintenance and Adjustments . . . . . . . .. . . ... . . ... . ... . ... . . .. . . ... . .... . . .. . . . .. . . .... . . .. . . . .. . . ... . . ... . . ... . . .. . . . . . . . .. . . .. . 1-62
General Repair Proceduces and Component Replacement . . . . ... . . ... . . . . . . . .. . . .... . . .. . . . .. . . .. . . . .. . . .. . . ... 1-63
Compressor Minor Overhaul Procedures ... . ... . ... . . .. . . ... . .... . . .. . . . .. . . .... . . .. . . . .. . . ... . . ... . . ... . . .. . . . . . . . .. . . .. . 1-72
Compressor Major Overhaul Procedures ... . ... . ... . . .. . . ... . . ... . . .. . . . .. . . .... . . .. . . . .. . . .... . ... . . ... . . .. . . . .. . . .. . . .. . 1-80
Leak Testing the Compressor .. . . .. . . . .. . . .. . . . .. . . .. . . .. . . . .. . . .. . . ... . . ... . . ... . . .. . . . ... . . ... . . .. . . . ... . ... . . ... . . .. . . ... . ... . 1-97
Air Conditioning Diagnosis . . .. . . . . . . . .. . . .... . ... . ... . ... . . .. . . ... . .... . . .. . . . .. . . ... . . ... . . . .. . . .. . . . ... . . ... . . .. . . . . . . . .. . . .. . 1-98
Vacuum Control Charts . . . . . . . . . . . . . . . . . ... . .. . . . ... . ... . ... . . ... . ... . .... . . .. . . . .. . . .... . . .. . . . .. . . ... . . ... . . ... . . .. . . . .. . . .. . . . 1-105
Special Tools . . . . . . . . . . . . . . . . .. . . . . .. . . . . . . . . . . . .. . . .. .. . .. . . ... . . .. . . ... . . .. . . ... . . .. . . . ... . . ... . . . . . . . .. . . . ... . ... . . ... . . .. . . . .. . . . . . . ..1-105