GMC chervolet camaro 1999 Service Manual page 220

HVAC
The V7 compressor is a variable displacement
compressor that can match the automotive air
conditioning demand under all conditions without
cycling. The basic compressor mechanism is a variable
angle wobble-plate with seven axially oriented
cylinders. A bellows actuated control valve located in
the rear head of the compressor senses the
compressor suction pressure and is the center of
control for the compressor displacement. The
crankcase-suction differential controls both the
wobble-plate and the compressor displacement. When
the A/C capacity demand is high, the suction
pressure will be above the control point. The control
valve will maintain a bleed from crankcase to
suction which causes no crankcase-suction pressure
differential giving the compressor 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 of a passage from the crankcase to the
suction plenum. The wobble-plate angle is controlled
by a force balance on the seven pistons. A slight
increase in the crankcase-suction pressure differential
creates a force on the pistons. This results in a
movement of the wobble-plate pivot pin that reduces
the plate angle.
T.he compressor has a unique lub(ication system. The
crankcase-suction bleed is routed through the
rotating wobble-plate for lubrication· qf the wobble-plate
bearing. The rotation acts an oil separator, removing
some of the oil from the crankcase-suction bleed,
and rerouting the oil to the crankcase where the oil can
lubricate the compressor mechanism.
High Pressure Relief Valve Description
The V7 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. The valve is designed to open automatically
at approximately 3036 kPa (440 psi) in order to
prevent system damage.
Correct any condition that causes the valve to open.
Replace refrigerant oil as necessary. Inspect the air
conditioning ,refrigerant pressure sensor for proper
calibration. Refer to
OTC P0530 Air Conditioning (AIC)
Refrigerant Pressure Sensor Circuit
in Engine
Controls-5. 7L.
HVAC System - Manual 1-129
Control Assembly Description (Chevrolet)
283259
The HV AC control head. uses three knobs and one
push button in order to control the following featur~s:
• The air delivery
• The air temperature
• The blower motor speed
• The rear defroster
Temperature Control Knob
The temperature control knob reg~.llates the HV AC
system air temperature. The knob is located in
the center of the HVAC control head. A temperature
control cable mechanically links the knob to the
temperature valve (door).
• Turn the knob toward the driver for heat.
• Turn the knob toward the passenger for A/C.
Mode Control Knob
The mode control knob is located on the right side of
the HV AC control head. The following are the eight
different modes:
• OFF
• MAX
• A/C
• Bl-LEVEL A/C
• VENT
• HEATER
• DEFROST/BLEND
• DEFROST
OFF
The following actions occur when the knob is in the
OFF position:
• The blower motor does not operate.
• Electrical power is not supplied to the
blower motor.
• An A/C request signal is not sent to the powertrain
control module (PCM).
• A small amount of air is forced into the HVAC
module by the forward movement of the vehicle.
The air is discharged through the heater and
defrost outlets.