System C O N Tro - GMC 1982 Light Duty Truck Service Manual

IB-4 AIR CONDITIONING
Fig. 1 B-3--Accumulator-C-K, & G Series With C60
evaporator core where it absorbs heat from the evaporator
core and changes to a low pressure vapor, and leaves the
evaporator core as such. The power element bulb is clamped
to the low pressure vapor line just beyond the outlet of the
evaporator (Fig. IB-2).
Accum ulator—C-K, & G Series (Fig. IB -3 )
The accumulator is located at the evaporator outlet. Its
most important function is not to "accum ulate" although
this too is important. Its primary function is to separate
liquid retained from vapor, retain the liquid and release the
vapor to the compressor.
Thus, in an ideal accumulator with no oil bleed hole,
and in a correctly designed system, no liquid can get to the
compressor.
In an actual accumulator, there is some entrained
liquid in the vapor stream to the compressor.
Flow out of the accumulator to the compressor consists
mostly of vapor with the addition of entrained liquid, and
liquid flow through the oil bleed hole.
A bag of desiccant (dehydrating agent) is located in the
accumulator as a moisture collecting device.
There is no sight glass in the accumulator-clutch cycle
system.
Expansion Tube—C-K, & G Series
Expansion tube flow rate depends on pressure
difference and on subcooling; however, the flow rate is more
sensitive to subcooling.
The expansion tube is located in the evaporator inlet
line (Fig. 1 B-4).
Therm ostatic Sw itch - M otor Hom e Chassis Units
O nly
System te m p e ra tu re is controlled by running the
compressor intermittently, automatically turning it on and
off as necessary to m aintain proper tem peratu res. The
compressor is started and stopped through the use of an
electro-m agnetic clutch and a th erm o sta t affected by
variations in temperature.
The thermostatic switch incorporates a metallic tube
which contains a highly expansive gas. This tube is located
in the air stream as it leaves the evaporator. The tube leads
to a bellows operated switch. As air temperature rises, the
gas inside the tube expands, travels through the tube to the
bellows and closes the electrical switch which engages the
compressor clutch.
As soon as the compressor starts running, the
temperature begins to go down. As the air being cooled gets
colder, the gas in the thermostatic tube begins to reduce the
pressure on the switch bellows. This allows the switch
contact to open and the compressor clutch disengages.
Pressure Cycling Sw itch - Low R efrigerant C harge
Protection System - C -K & G Series
Low refrigerant charge protection is afforded by the
pressure cycling switch as a secondary function. W hen
refrigerant pressure drops below a certain predetermined
level, the switch opens the compressor clutch circuit,
shutting the system OFF.
SYSTEM CONTROLS
C 6 0 SYSTEM (C-K & G SERIES) - FIG. IB -5
System O peration - C-K Truck
System operation is shown in Fig. 1 B-6.
Fig. 1 B-4--Expansion Tube