differential CHEVROLET DYNASTY 1993 Repair Manual

COMPONENT SERVICE PROCEDURES INDEX
page page
Air Distribution Duct ...................... 50
Air Distribution Duct ...................... 52
Ambient Switch .......................... 47
Blend-Air Door .......................... 64
Blower Motor ............................ 58
Blower Motor Wheel Assembly .............. 58
Blower Resistor Block ..................... 49
Condensate Drain Tube ................... 64
Condenser Assembly ...................... 57
Condenser Fan Control Switch .............. 47
Defroster Duct ........................... 51
Defroster Duct Adapter .................... 51
Defroster Ducts/Demister Ducts and Hoses ..... 52
Differential Pressure Cut-Out Switch Diagnosis . . 48
Evaporator Coil .......................... 64 Expansion Valve
......................... 55
Filter-Drier Assembly ...................... 57
Fin-Sensing Cycling Clutch Switch ............ 53
Heater Core ............................ 64
Heater Hoses ........................... 51
Heater-A/C Unit AssemblyÐRemoval and Installation ............................ 61
Heater-A/C Unit Recondition ................ 63
Low or Differential Pressure Cut-Off Switch ..... 54
Temperature Control CableÐAA,AP,AG and AJ Models ............................ 49
Temperature Control CableÐAC/AY Models .... 48
Vacuum ActuatorÐFresh/Recirc Door ......... 50
Vacuum ActuatorsÐMode Doors ............. 52
AMBIENT SWITCH
The ambient switch is a temperature sensor located
in front of the condenser behind the grille (Fig. 1).
The ambient switch prevents the compressor from
engaging in cold temperatures. The ambient switch
is a sealed factory calibrated unit. It must be re-
placed if defective.
AMBIENT SWITCH TEST
(1) Disconnect ambient switch wire connector.
(2) Using a suitable ohm meter or continuity
tester, test for continuity across the ambient switch
terminals. (a) At temperature above 10ÉC (50ÉF), the switch
circuit should be complete. (b) Chill the switch with ice to below 10ÉC (50ÉF)
and test for continuity. The switch circuit should
be open, with continuity not detected.
Replace ambient switch if defective.
REMOVAL AND INSTALLATION
(1) Remove the one attaching screw.
(2) Remove the sensor/bracket assembly from the
vehicle. To install, reverse the preceding operation.
CONDENSER FAN CONTROL SWITCH
The Fan Control Switch is located on the plumbing
discharge line at the A/C compressor (Fig. 2). The fan
control switch cycles the radiator/condenser fan on and
off by monitoring the compressor discharge pressure.
The radiator top tank temperature sensor can over ride
the function of the fan control switch. It can cycle the
radiator/condenser fan on and off depending on the
engine temperature.
FAN CONTROL SWITCH DIAGNOSIS
Review Safety Precautions and Warnings before pro-
ceeding. Connect a manifold gauge set to the refriger-
ant system service ports. Work area temperature can
not be below 21ÉC (70ÉF).
Fig. 1 Ambient Temperature Sensor SwitchÐTypical Mounting
Fig. 2 Condenser Fan Control Switch
Ä HEATING AND AIR CONDITIONING 24 - 47

WARNING: AVOID RADIATOR/CONDENSER FAN
BLADES WHEN WORKING IN THE RADIATOR
AREA. FAN IS CONTROLLED BY TEMPERATURE
AND CAN START ANY TIME IGNITION IS ON. PER-
SONAL INJURY CAN RESULT.
(1) Disconnect fan control switch wire connector.
(2) Using a suitable jumper wire, jump across ter-
minals in wire connector. (3) Connect a suitable continuity tester across fan
control switch terminals. (4) Start engine and set idle at 1300 rpm. The ra-
diator fan should run constantly. (5) Set the A/C controls to A/C and high blower.
(6) If the high pressure gauge reads below 1102
kPa (160 psi) there should be no continuity across
the switch terminals.
CAUTION: Do not allow engine to overheat when ra-
diator air flow is blocked.
(7) Block radiator air flow with a suitable cover to
increase the high side pressure to at least 1585 kPa
(230 psi). Electrical continuity should be detected
across the fan control switch terminals. (8) Remove cover from front of vehicle to allow
high side pressure to decrease. When pressure drops
below 1102 kPa (160 psi), continuity should cease. If fan control switch is defective, replace it.
REMOVAL AND INSTALLATION
CAUTION: Refrigerant removal is not necessary
when removing the Condenser Fan Control Switch.
However, a small amount of refrigerant will vent
from the switch port. Review the refrigerant han-
dling section of Safety Precautions and Warnings in
the General Information section of this Group.
(1) Disconnect wire connector from condenser fan
control switch. (2) Loosen and quickly rotate the switch counter-
clockwise and separate from the high pressure line
switch port. To install, reverse the preceding operation.
DIFFERENTIAL PRESSURE CUT-OUT SWITCH
DIAGNOSIS
The Differential Pressure Cut-Out (DPCO) Switch
(Fig. 3) monitors the liquid refrigerant pressure on
the liquid side of the system. The DPCO is located on
the expansion valve. The expansion valve is black in
color when a variable displacement compressor is
used. The DPCO turns off voltage to the compressor
clutch coil when liquid refrigerant pressure drops to
levels that could damage the compressor. The DPCO
is a sealed factory calibrated unit. It must be re-
placed if defective.
DPCO SWITCH DIAGNOSIS
The work area must not be below 10ÉC (50ÉF) to
test the compressor clutch circuit. (1) With gear selector in park or neutral, and park
brake set, start engine and allow to idle. (2) Raise hood and disconnect DPCO switch con-
nector boot. (3) Using a suitable jumper wire, jump across the
terminals inside wire connector boot. (4) If clutch does not engage, the wiring, fuse, re-
lay, ambient switch, or high pressure cut-off switch
can be defective. Refer to Group 8W, Wiring Dia-
grams. (5) If clutch engages, connect a suitable manifold
gauge set. Read low pressure gauge. At pressure 283
kPa (41 psi) and above, DPCO switch will complete
the clutch circuit. If the low pressure gauge reads be-
low 317 kPa (46 psi), the system is low on refrigerant
charge or empty due to a leak. Refer to Testing For
Refrigerant Leaks in the Refrigerant Service Proce-
dures section. (6) Install connector boot on switch and repeat step
number 3. If the clutch does not engage, replace the
DPCO switch.
TEMPERATURE CONTROL CABLEÐAC/AY MODELS
REMOVAL AND INSTALLATION
A Temperature Control Cable is used on non-ATC
heat or heater-A/C systems only. ATC (Automatic
Temperature Control) systems use an electrically op-
erated temperature control. Refer to the ATC section
of this Group. (1) Remove the A/C-Heater control panel assembly.
Refer to A/C-Heater Control Replacement in Group
8E Instrument Panel. Disconnect the cable attaching
flag from the A/C-heater control and remove the ca-
ble from control panel.
Fig. 3 Differential Pressure Cut-Out Switch
24 - 48 HEATING AND AIR CONDITIONING Ä

housing) through the hole in the housing. Feed the
wire harness and connector through the opening and
into the housing (Fig. 19). (3) Work through the air inlet opening (to the left of
the blower motor wheel). Pull the fin-sensing cycling
switch from the A/C evaporator (Fig. 20). The metal
probe on the switch is pushed into the evapora-
tor approximately three inches.
To install, reverse the preceding operation. The
switch probe should not be installed in the original
location (hole). Insert the probe in the evaporator coil
approximately 5 mm (3 to 4 fins) to the right or left of
the position it was removed. This will insure correct
temperature sensing and system performance. Exces-
sive force should not be required for probe insertion.
Care should be taken not to damage the A/C evaporator
coil or the switch probe.
LOW OR DIFFERENTIAL PRESSURE CUT-OFF
SWITCH
The Low Pressure Cut-Off (LPCO) Switch (Fig. 21)
monitors the refrigerant gas pressure on the suction side of the system. The LPCO is located on the ex-
pansion valve, and the expansion valve is silver in
color when a fixed displacement compressor is used.
The LPCO turns off voltage to the compressor clutch
coil when refrigerant gas pressure drops to levels
that could damage the compressor. The LPCO is a
sealed factory calibrated unit. It must be replaced if
defective.
LPCO SWITCH DIAGNOSIS
The work area must not be below 10ÉC (50ÉF) to
test the compressor clutch circuit. (1) With gear selector in park or neutral and park
brake set, start engine and allow to idle. (2) Raise hood and disconnect LPCO switch con-
nector boot. (3) Using a suitable jumper wire, jump across the
terminals inside wire connector boot. (4) If the compressor clutch does not engage, the
cycling clutch switch, wiring, relay, or fuse can be
defective. Refer to Group 8W, Wiring Diagrams. (5) If clutch engages, connect manifold gauge set.
Read low pressure gauge. At pressure above 97 kPa
(14 psi) and above, LPCO switch will complete the
clutch circuit. If the low pressure gauge reads below
172 kPa (25 psi), the system is low on refrigerant
charge or empty due to a leak. Refer to Testing For
Refrigerant Leaks in the Refrigerant Service Proce-
dures section. (6) Install connector boot on switch and repeat step
number 3. If the clutch does not engage, replace the
LPCO switch.
REMOVAL AND INSTALLATION
WARNING: THE REFRIGERATION SYSTEM MUST
BE COMPLETELY EMPTY BEFORE PROCEEDING
WITH THIS OPERATION. REFER TO REFRIGERANT
RECOVERY SECTION.
Fig. 21 Low Pressure Cut-Off Switch
Fig. 19 Remove or Install Wire Harness Grommet
Fig. 20 Remove or Install Fin-sensing Cycling Clutch Switch
24 - 54 HEATING AND AIR CONDITIONING Ä

(1) Disconnect the boot like wire connector at the
cut-off switch. (2) Using a sender unit type socket, remove the
switch from the expansion valve (Fig. 22 or 23).
To install, assure an adequate seal by using a small
amount of thread sealing tape on the replacement
switch and reverse the preceding steps. Evacuate and charge the system.
EXPANSION VALVE
DIAGNOSIS
BLACK EXPANSION VALVE TEST
Liquid CO
2is required to test the expansion
valve. It is available from most welding supply
facilities. CO
2is also available from companies
which service and sell fire extinguishers. Review Safety Precautions and Warnings before pro-
ceeding with this operation. The work area must be 21ÉC to 27ÉC (70ÉF to 85ÉF) when testing expansion
valve. To test the expansion valve: (1) Connect a charging station or manifold gauge set
to the refrigerant system service ports. (2) Verify the refrigerant charge level using the sight
glass method. (3) Disconnect the wire connector at the differential
pressure cut-off switch. Using a jumper wire, jump
across the terminals inside the connector boot (Fig. 24).
(4) Close all doors, windows and vents to the passen-
ger compartment. (5) Set heater-A/C control to A/C, full heat, FLOOR,
and high blower. (6) Start the engine and hold the idle speed (1000
rpm). After the engine has reached running tempera-
ture, allow the passenger compartment to heat up.
This will create the need for maximum refrigerant flow
into the evaporator. (7) Discharge (high pressure) gauge should read 965
to 1655 kPa (140 to 240 psi) when the refrigerant
charge is sufficient. If system cannot achieve proper
pressure, replace the expansion valve. If pressure is
correct, record reading and proceed with test.
WARNING: PROTECT SKIN AND EYES FROM CON-
TACTING CO
2PERSONAL INJURY CAN RESULT.
(8) If discharge pressure is within specified range,
freeze the expansion valve control head (Fig. 8) for
30 seconds. Use a super cold substance (liquid
CO
2). Do not spray R-12 Refrigerant on the expan-
sion valve for this test. Refer to Refrigerant
Recycling in the Refrigerant Service Procedures
section. If compressor discharge (high) pressure does
not drop by 15% or more than the pressure recorded in
step 7, replace the expansion valve. Allow the expan-
sion valve to thaw. The discharge pressure should
Fig. 22 Low Pressure Cut-Off Switch and Expansion ValveÐTypical
Fig. 23 Differential Pressure Cut-Off Switch and Ex-pansion ValveÐTypical
Fig. 24 Differential Pressure Cut-Out Switch
Ä HEATING AND AIR CONDITIONING 24 - 55