Chevrolet Light Duty Truck 1973, Service Manual

Page: 60 / 979

1A -34 HEATER A N D AIR C O N D IT I O N I N G
Fig. 38--Accumulator
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. The measure of a
good accumulator is how well it separates vapor from
liquid and how little entrained liquid is released to the
compressor. Also, in an actual accumulator, an oil bleed
hole is required to prevent trapping of oil in the bottom
of the accumulator; this oil bleed hole bleeds some liquid
refrigerant as well.
Therefore, 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
base of the accumulator as a moisture collecting device.
NOTE: There is no sight glass in the
accumulator clutch cycle system.
Expansion Tube--C-K Models
Expansion tube flow rate depends on pressure difference
and on subcooling; however, the flow rate is more
sensitive to subcooling.
Fig. 39-Expansion Tube
The expansion tube is located in the enlarged portion of
the evaporator inlet line.
Thermostatic Switch
System temperature is controlled by running the
compressor intermittently, automatically turning it on
and off as necessary to maintain proper temperatures.
The compressor is started and stopped through the use of
an electro-magnetic clutch and a thermostat affected by
variations in temperature.
The thermostatic switch incorporates a metallic tube
which contains a highly expansive gas. This tube is
inserted into the evaporator core (C-K Four-Season
System) or is located in the air stream as it leaves the
evaporator (all other systems). 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 contacts to open and the compressor clutch
disengages.
Low Refrigerant Charge Protection System
C-K Models
The compressor discharge pressure switch performs the
function of shutting off the compressor when it senses
low refrigerant pressure. The switch is located in the
evaporator inlet line (high pressure). The switch
electrically is wired in series between the compressor
clutch and the master switch on the control. When the
switch senses low pressure it breaks contact and opens
the circuit to the compressor clutch, thus shutting off the
A/C system and preventing compressor failure or
seizure.
“ O ” RING
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INLET
LIGHT DUTY TRUCK SERVICE MANUAL