The V5 A/C System
The V5 variable displacement compressor along with the thermal expansion
valve on the evaporator, constitutes a largely self-regulating system. There is no
pressure cycling switch, no high-pressure cut-off switch and no low-pressure cut-off
switch. The compressor clutch is controlled by the electronic control module (ECM),
which receives data from various engine systems and from a pressure transducer located
in the high-pressure refrigerant pipe. In normal operation, the clutch is engaged
continuously. Should one of the monitored conditions become abnormal, the ECM will
disengage the compressor clutch until normal operation is restored. This incudes the
following conditions:
| • | High engine coolant temperature |
| • | Refrigerant low pressure |
| • | Refrigerant high pressure |
The compressor clutch will remain disengaged until normal operation is established.
System Components - Functional
Compressor
All compressors are belt-driven from the engine crankshaft through the compressor
clutch pulley. The compressor pulley rotates without driving the compressor 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. The refrigerant
oil which is used to lubricate the compressor is carried with the refrigerant.
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. In order to prevent system damage,
the valve is designed to open automatically at approximately 3 171-4 137 kPa
(460-600 psi) in an R-134a system. Conditions that might cause
this valve to open, such as a defective pressure transducer, an inoperative cooling
fan, etc., should be corrected. The refrigerant oil and the refrigerant should be
replaced as necessary.
Condenser Core
The condenser assembly in front of the radiator consists of coils which carry
the refrigerant, and cooling fins that provide the rapid transfer of heat. The air
passing through the condenser cools the high-pressure refrigerant vapor and causes
it to condense into a liquid.
Expansion Valve
The expansion valve is located with the evaporator core, inside the heater/air
distributor case under the instrument panel.
The expansion valve can fail in 3 different positions:
| • | Open - An expansion valve that fails in the open position will result
in a noisy A/C compressor or no cooling. The cause can be a broken spring, a broken
ball, or excessive moisture in the A/C system. If the spring or the ball are found
to be defective, replace the expansion valve. If excessive moisture is found in the
A/C system, recycle the refrigerant. |
| • | Closed - An expansion valve that fails in the closed position will
result in low suction pressure and no cooling. This may be caused by a failed power
dome or excessive moisture in the A/C system. If the power dome on the expansion valve
is found to be defective, replace the expansion valve. If excessive moisture is found
in the A/C system, recycle the refrigerant. |
| • | Restricted - A restricted expansion valve will result in low suction
pressure and no cooling. This may be caused by debris in the refrigerant system. If
debris is believed to be the cause, recycle the refrigerant, replace the expansion
valve, and replace the receiver-dryer. |
Evaporator Core
The evaporator is a device which cools and dehumidifies the air before it enters
the vehicle. High-pressure liquid refrigerant flows through the expansion tube orifice
and becomes a low-pressure gas in the evaporator. The heat in the air passing through
the evaporator core is transferred to the cooler surface of the core, which cools
the air. As the process of heat transfer from the air to the evaporator core surface
is taking place, any moisture or humidity in the air condenses on the outside surface
of the evaporator core and is drained off as water.
Receiver-Dryer
The sealed receiver-dryer assembly is connected to the condenser outlet pipe.
It acts as a refrigerant storing container, receiving liquid, vapor, and refrigerant
oil from the evaporator.
At the bottom of the receiver-dryer is the desiccant, which acts as a drying
agent for the moisture that may have entered the system. An oil bleed hole is located
near the bottom of the receiver-dryer outlet pipe to provide an oil return path to
the compressor. The receiver-dryer is serviceable only as an assembly.
Heater Core
The heater core heats the air before it enters the vehicle. Engine coolant is
circulated through the core to heat the outside air passing over the fins of the core.
The core is functional at all times and may be used to temper conditioned air in the
A/C mode as well as in the heat or the vent modes.
System Components - Control
Controller
The operation of the A/C system is controlled by the switches on the control
head. This console-mounted heating and ventilation panel contains the following:
Three Rotary Control Knobs
| • | The Rotary Temperature Control Knob |
| - | Varies the mix of the fresh air from outside the vehicle with the heated
air from inside the vehicle to suit individual preference |
| - | Raises the temperature of the air entering the vehicle by rotation toward
the right, or the red portion of the knob |
| • | The Rotary Mode Control Knob |
| - | Regulates the air distribution between the windshield, the instrument
panel, and the floor vents |
| • | The Rotary Blower Control Knob |
| - | Turns on to operate the blower motor at 4 speeds |
| - | Turns OFF to stop the blower |
| - | Operates completely independently from both the mode control knob, that
regulates the defroster door, and the temperature control knob |
| - | Changes the fan speed in any mode and at any temperature setting--However,
if the rotary blower control knob is OFF, the A/C system is OFF, regardless of the
position of the A/C push knob |
Three Push Knobs
| - | Turns the A/C on when the push knob is pressed and the indicator lamp
is illuminated--The rotary blower control knob must be in 1 of its 4 positions
for the A/C to function. |
| • | The Rear Window Defogger Push Knob |
| - | Controls the rear window defogger |
| - | Turns on the rear window defogger when the push knob is pressed and the
indicator lamp is illuminated |
| • | The Fresh Air Control Push Knob |
| - | Switches between recirculating passenger compartment air or bringing outside
air into the passenger compartment |
| - | Defaults to fresh air mode--The indicator lamp is illuminated when
recirculation is selected. |
| - | Operates the inlet air door by vacuum |
The electric engine cooling fans are operational any time the A/C control is
on. This added feature is part of the A/C controller function and is aimed at preventing
excessive compressor head temperatures. It also allows the A/C system to function
more efficiently. The operation of the cooling fans is controlled by the ECM through
the cooling fan relays.
Vacuum Lines
Vacuum lines are molded to a connector, which is attached to a vacuum control
switch on the control head assembly.
In case of leakage or hose collapse, it will not be necessary to replace the
entire harness assembly. Replacement can be made by cutting the hose and inserting
a plastic connector. If an entire hose must be replaced, cut all the hoses off at
the connector and attach hoses directly to the control head vacuum switch.
Vacuum Tank
During heavy acceleration, the vacuum supply from the manifold drops. A check
valve in the vacuum tank maintains vacuum so that under load conditions vacuum will
be available for continuous use.
Pressure Transducer
Pressure transducer switching incorporates the functions of the high-pressure
and the low-pressure cutout switches along with the fan cycling switch. The pressure
transducer is located in the high-side liquid refrigerant line behind the right headlamp,
between the right front inner fender and the air filter assembly. The output from
this pressure transducer goes to the ECM which controls the compressor function based
on the pressure signal.
Wide-Open Throttle (WOT) Compressor Cutoff
During full throttle acceleration, the throttle position sensor (TPS)
sends a signal to the ECM, which then controls the compressor clutch.
V5 Compressor - General Description
Vehicles using the V5 compressor may have differences between installations
in the mounting brackets, the drive systems, the pulleys, the connections, and the
system capacities. Basic overhaul procedures are similar between the compressors used
on different vehicles.
When servicing the compressor, keep dirt and foreign material from getting on
or into the compressor parts and the system. Clean tools and a clean work area are
important for proper service. The compressor connections and the outside of the compressor
should be cleaned before undertaking any on-vehicle repairs and before the removal
of the compressor. The parts must be kept clean at all times. Any parts that are to
be reassembled should be cleaned with trichloroethane, naphtha, stoddard solvent,
kerosene, or equivalent solvents and dried with dry air. Use only lint-free cloths
to wipe the parts.
Important: The oil drain plug must be removed and the
oil drained through the plug opening to insure complete draining of the oil from the
compressor.
The operations described are based on bench overhaul with the compressor removed
from the vehicle, except as noted. They have been prepared in the order of accessibility
of the components. When a compressor is removed from the vehicle for servicing, the
amount of oil remaining in the compressor should be drained, measured, and recorded.
This oil should then be discarded and new polyalkaline glycol (PAG) refrigerant
oil added to the compressor.
V5 Compressor - Description of Operation
The V5 is a variable displacement compressor that can match the automotive A/C
demand under all conditions without cycling. The basic compressor mechanism is a variable
angle wobble-plate with five axially oriented cylinders. The center of control of
the compressor displacement is a billows-actuated control valve located in the rear
head of the compressor that senses compressor suction pressure.
The wobble-plate angle and the compressor displacement are controlled by the
crankcase suction pressure differential. When the A/C capacity demand is high, the
suction pressure will be above the control point. The valve will maintain a bleed
from crankcase to suction. With no crankcase-suction pressure differential, the compressor
will have maximum displacement.
When the A/C capacity demand is lower and the suction pressure reaches the control
point, the valve will bleed discharge gas into the crankcase and close off a passage
from the crankcase to the suction plenum. The angle of the wobble-plate is controlled
by a force balance on the 5 pistons. A slight elevation of the crankcase suction
pressure differential creates total force on the pistons resulting in a movement about
the wobble-plate pivot pin that reduces the plate angle.
The compressor has a unique lubrication system. The crankcase suction bleed
is routed through the rotating wobble-plate for lubrication of the wobble-plate bearing.
The rotation acts as an oil separator which removes some of the oil from the crankcase
suction bleed, re-routing it to the crankcase where it can lubricate the compressor
mechanism.
