A/C System; A/C System Differences; System Components - Functional - Pontiac Fiero 1988 Service Manual

1B-2
AIR CONDITIONING
The C.C.O.T, A/C System
The Cycling Clutch Orifice Tube (C.C.O.T.)
refrigeration system is designed to cycle a compressor
on and off to maintain desired cooling and to prevent
evaporator freeze. Passenger compartment comfort is
maintained by the temperature lever on the controller.
Control of the refrigeration cycle (on and off
operation of the compressor) is done with a switch
which senses low-side pressure as an indicator of
evaporator temperature. The pressure cycling switch
is the freeze protection device in the system and
senses refrigerant pressure on the suction side of the
system. This switch is located on a standard Schrader-
type valve low-side fitting. During air temperatures
over 10°C (50°F), the equalized pressures within the
charged A/C system will close the contacts of the
pressure switch. When an air conditioning mode
(max, norm, bi-level, defrost) is selected, electrical
energy is supplied to the compressor clutch coil. As
the compressor reduces the evaporator pressure to
approximately 175 kPa (25 psi), the pressure switch
will open, de-energizing the compressor clutch. As
the system equalizes and the pressure reaches approxi-
mately 315 kPa (46 psi), the pressure switch contacts
close, re-energizing the clutch coil. This cycling con-
tinues and maintains average evaporator discharge air
temperature at approximately 1°C (33°F). Because of
this cycling, some slight increases and decreases of
engine speed/power may be noticed under certain con-
ditions. This is normal as the system is designed to
cycle to maintain desired cooling, thus preventing
evaporator freeze-up.
A/C S Y S T E M DIFFERENCES
P r e s s u r e C y c l i n g
Switch
The pressure cycling switch is not used with V-5
A/C systems because the compressor can vary its dis-
placement to match the automotive air conditioning
demand under all conditions. The switch is still used
with all C.C.O.T. type systems (see pressure cycling
switch under S Y S T E M C O M P O N E N T S —
CONTROL).
Low Pressure Cut-Out Switch
Because the pressure cycling switch is not used
with the V-5 compressor, a low pressure cut-out
switch is used to protect the compressor from a low
charge condition. The low pressure cut-out switch,
located in the rear head of the compressor next to the
high pressure cut-out switch, is also used to shut the
compressor off in cold weather (see Low-Pressure
Cut-Off Switch under SYSTEM COMPONENTS —
CONTROL).
V - 5 Compressor Removal
The V-5 Compressor is equipped with a crank-
case drain plug located in the body of the compressor.
When removing the V-5 and draining oil from the
compressor, the crankcase plug must be removed and
oil drained from the fitting. It is also necessary to
drain the oil from the suction and discharge ports to
assure complete oil draining. (See Section 1D3 for
complete instructions on removal or replacement of a
V-5 compressor.)
The R-4 and HR-6 compressors do not have a
crankcase and oil can only be drained from the suction
and discharge ports.
S Y S T E M COMPONENTS — FUNCTIONAL
C o m p r e s s o r
All compressors are belt driven from the engine
crankshaft through the compressor clutch pulley. The
compressor pulley rotates without driving the com-
pressor shaft until an electromagnetic clutch coil is
energized. When voltage is applied to energize the
clutch coil, the clutch plate and hub assembly is
drawn rearward toward the pulley. The magnetic
force locks the clutch plate and pulley together as one
unit to drive the compressor shaft.
As the compressor shaft is driven, it compresses
the low-pressure refrigerant vapor from the evaporator
into a high-pressure, high-temperature vapor. Carried
with the refrigerant is the refrigerant oil which is used
to lubricate the compressor. Complete compressor
overhaul procedures can be found in Section ID of the
General Service Manual.
Pressure Relief Valve
The compressor is equipped with a pressure
relief valve which is placed in the system as a safety
factor. Under certain conditions, the refrigerant on the
discharge side may exceed the designed operating
pressure. To prevent system damage, the valve is
designed to open automatically at approximately 3036
kPa (440 psi). Conditions that might cause this valve
to open (defective high pressure cut-off switch, inop-
erative electric cooling fan, etc.) should be corrected,
and the refrigerant oil and refrigerant should be
replaced as necessary.
Muffler
A muffler is used on some refrigerant systems to
reduce compressor noises from high or low pressure
vibrations.
Condenser Core
The condenser assembly in front of the radiator
is made up of coils which carry the refrigerant to
cooling fins to provide rapid transfer of heat. The air
passing through the condenser cools the high-pressure
refrigerant vapor causing it to condense to a liquid.
Expansion (Orifice) Tube
The plastic expansion tube, with its mesh screen
and orifice, is located in the evaporator inlet pipe at