FRONT (ONLY)
(1) Attach a manifold gauge set. Close the vehicle
doors and windows, start the engine, and hold the
engine speed at 1,000 rpm. Set the heater-A/C mode
control switch knob to the recirculation mode (Max
A/C) position, the temperature control knob to the
full hot position, and the blower motor switch to the
highest speed position.
(2) Operate the air conditioning system for at least
five minutes to stabilize the system, and to provide
sufficient reheat to load the evaporator. The dis-
charge pressure (high side) at the service port should
reach 966 to 1656 kPa (140 to 240 psi). If this dis-
charge pressure cannot be obtained, check the refrig-
erant system charge. See Refrigerant System Charge
in the Service Procedures section of this group.
WARNING: EXTREME CARE MUST BE USED WHEN
HANDLING LIQUID CARBON DIOXIDE (CO
2
), AS
SKIN INJURY CAN OCCUR. PROTECTIVE GLOVES
SHOULD BE WORN.
(3) Apply liquid carbon dioxide (CO
2
) to the expan-
sion valve control head (completely cover the head)
for a minimum of thirty seconds. Observe the mani-
fold gauge set. The suction pressure (low side) must
drop to below 50 kPa (7.25 psi). If this reading is not
obtained, the expansion valve is faulty and must be
replaced.
(4) Remove the liquid carbon dioxide (CO
2
) from
the control head. Observe the manifold gauge set.
The suction pressure (low side) must increase to a
minimum of 262 kPa (38 psi), and then stabilize to a
pressure of 172 to 240 kPa (25 to 35 psi). If these
readings are not obtained, the expansion valve is
faulty and must be replaced.
(5) Set the engine idle speed at 1,000 rpm and the
blower motor switch to the highest speed position.
The suction pressure (low side) should be 138 to 207
kPa (20 to 30 psi). If the discharge pressure (high
side) is higher than 1656 kPa (240 psi), check for a
restricted discharge line. Also check the engine cool-
ing system for overheating, air trapped in the sys-
tem, or a faulty fan drive. If the discharge pressure
(high side) is less than 966 kPa (140 psi), check for a
faulty compressor.
FRONT AND REAR A/C
(1) Attach a manifold gauge set. Close the vehicle
doors and windows, start the engine, and hold the
engine speed at 1,000 rpm. Set the heater-A/C mode
control switch knob to the recirculation mode (Max
A/C) position, the temperature control knob to the
full hot position, and both the front and rear blower
motor switches to their highest speed positions.
(2) Operate the air conditioning system for at least
five minutes to stabilize the system, and to provide
sufficient reheat to load the front and rear evapora-
tors. The discharge pressure (high side) at the service
port should reach 966 to 1656 kPa (140 to 240 psi). If
this discharge pressure cannot be obtained, check the
refrigerant system charge. See Refrigerant System
Charge in the Service Procedures section of this
group.
WARNING: EXTREME CARE MUST BE USED WHEN
HANDLING LIQUID CARBON DIOXIDE (CO
2
)AS
SKIN INJURY CAN OCCUR. PROTECTIVE GLOVES
SHOULD BE WORN.
(3) Both the front and rear expansion valves
should be checked for correct operation. Apply liquid
carbon dioxide (CO
2
) to the front expansion valve
control head (completely cover the head) for a mini-
mum of thirty seconds. Observe the manifold gauge
set. The suction pressure (low side) must drop to
below 50 kPa (7.25 psi). If this reading is not
obtained, the expansion valve is faulty and must be
replaced.
(4) Apply liquid carbon dioxide (CO
2
) to the front
expansion valve control head (completely cover the
head) for a minimum of thirty seconds. Remove the
protective cover and apply liquid carbon dioxide
(CO
2
) to the rear expansion valve control head.
Grasp the suction line (large line) off the evaporator
with a bare hand and hold it for at least two min-
utes. Use the same procedure with the front expan-
sion valve. Grasp the suction line jumper below the
expansion valve (before the rear suction line tee)
with a bare hand and hold for at least two minutes.
When testing the front expansion valve, place the
rear blower motor switch in the Off position.
(5) With a correctly operating expansion valve, the
suction line will feel warm with the closing of the
valve (cold applied). Then the line will cool sharply
within two minutes as the valve opens. If this tem-
perature change does not occur, the expansion valve
is faulty and must be replaced.
HEATER-A/C CONTROL
Satisfactory heater and air conditioner perfor-
mance depends upon proper operation and adjust-
ment of all operating controls and refrigeration
system components. For circuit descriptions and dia-
grams, refer to 8W-42 - Air Conditioning/Heater in
Group 8W - Wiring Diagrams. These inspections,
tests, and adjustments should be used to locate the
cause of a malfunction.
Operation must be tested as described in the fol-
lowing sequence:
(1) Move the temperature control knob quickly to
the full hot and the full cold positions. There should
be a distinct sound of the blend-air door hitting its
stops within the heater-A/C housing at the end of
24 - 20 HEATING AND AIR CONDITIONING DN
DIAGNOSIS AND TESTING (Continued)
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