heater CHEVROLET DYNASTY 1993 Manual PDF

AA BODY PROCEDURE
WARNING: IF EQUIPPED WITH A/C, THE REFRIG-
ERATION SYSTEM MUST BE COMPLETELY EMPTY
BEFORE PROCEEDING WITH THIS OPERATION. Refer to Group 8E and Group 23 for component re-
moval and installation when performing this opera-
tion. (1) Perform steps 1 through 7 of Blower Motor re-
moval and installation. (2) Remove relay panel above glove compartment
opening. (3) Disconnect the A/C vacuum line connector and
radio noise capacitor connectors. (4) Remove left windshield pillar trim cover.
(5) Remove left lower side cowl trim cover.
(6) Remove hood release handle mechanism attach-
ing screws. (7) Remove steering column trim covers.
(8) Disconnect parking brake release mechanism
connecting rod. Gain access through fuse panel open-
ing. (9) Remove lower left instrument panel silencer.
(10) Remove lower left instrument panel reinforce-
ment. (11) Remove instrument panel center (radio) bezel.
(12) Remove forward floor console.
(13) Remove the radio.
(14) Remove the heater-A/C control.
(15) Remove cigar lighter.
(16) Remove message center/trip computer, if
equipped. (17) Disconnect side window demister tubes from
top of heat A/C unit. (18) Remove steering column upper attaching bolts
and allow the steering wheel to rest on the driver
seat cushion. (19) Remove upper instrument panel (defroster
outlet) cover. (20) Remove upper instrument panel attaching
screws from below the windshield opening. (21) Loosen (do not remove) the left lower cowl in-
strument panel attaching screw. (22) Remove the right lower cowl instrument panel
attaching screw.
CAUTION: Protect the passenger seat cover from
soiling or damage using a suitable cover.
(23) Carefully pull the right side of the instrument
panel away from the vehicle. Allow the instrument
panel to rest on the passenger seat cushion.
CAUTION: Before proceeding with the next opera-
tion, review the Safety Precautions and Warnings at
the front of this Group. (24) From the engine compartment, drain the cool-
ing system and disconnect the heater hoses from the
heater core nipples. Plug the nipples to avoid spilling
coolant inside the vehicle. (25) Disconnect the refrigerant lines from the ex-
pansion-valve at the dash panel on the right side of
the vehicle. Seal the refrigerant lines to prevent con-
tamination. (26) Remove the expansion valve from the evapo-
rator plate. Seal the valve to avoid contamination. (27) Remove the condensate drain tube.
(28) Remove heater-A/C unit to dash panel attach-
ing nuts. (29) From inside the vehicle, pull rearward on the
heater-A/C unit to clear the dash panel silencer and
remove the unit from the vehicle. To install, reverse the preceding operation. Refill
cooling system and test for leaks. Evacuate and
charge the refrigerant system and test overall perfor-
mance.
AG, AJ BODY PROCEDURE
WARNING: IF EQUIPPED WITH A/C, THE REFRIG-
ERATION SYSTEM MUST BE COMPLETELY EMPTY
BEFORE PROCEEDING WITH THIS OPERATION.
(1) Disconnect the battery negative cable.
(2) Drain the coolant from cooling system. Refer to
Group 7, Cooling System. (3) Remove the air conditioner expansion valve (if
equipped). (4) Disconnect the heater hoses from heater core.
Then plug or cap the tubes on heater core. This will
prevent spilling coolant into the interior of vehicle
during unit removal. (5) Remove the condensate drain tube.
(6) Disconnect the A/C-heater vacuum supply line
from vacuum supply nipple (in the engine compart-
ment). (7) Remove the four A/C-heater assembly-to-dash
panel attaching nuts. (8) Remove the passenger side front seat. Refer to
Group 23, Body. (9) Remove the kick panel/sill cover at right door
opening. (10) Remove the body computer (Fig. 6) located at
the lower right section of the right front door pillar. (11) Remove the glove box assembly. Refer to
Group 8E, Instrument Panel. (12) Remove the carpeted panels from both sides of
the console. (13) Un-clip the radio antenna cable from the
metal support (Fig. 6) located behind and below the
glove box opening. (14) Instrument panel removal is not necessary to
remove the A/C-heater assembly from the vehicle.
24 - 62 HEATING AND AIR CONDITIONING Ä

Although, part of the lower instrument panel must
be cut. The cut line is marked: CUT HERE FOR
A/C HTR REMOVAL. This cut line is stamped (indented) into the right-
outer side of the instrument panel padding (outboard
of the glove box opening). Using a hacksaw blade,
cut the instrument panel padding along the indented
line from point A to point B (Fig. 7). CUT THE
PLASTIC ONLY . Do not cut the metal support be-
hind the instrument panel padding.
(15) Remove the metal support behind and below
the glove box opening, and the previously cut piece of
the instrument panel that is riveted to it. (16) Remove the radio choke, security alarm mod-
ule and the lamp outage module from above the
glove box opening (if equipped). (17) Remove the plastic cover under the steering
column. (18) Remove the metal support under the steering
column. (19) AJ Body only: Remove the under-panel si-
lencer pad from under the glove box opening. (20) Remove the lower heat distribution duct (3
screws). (21) Remove the air distribution duct through the
opening at the left side of instrument panel. (22) Reach through glove box opening and discon-
nect the demister hoses from the top of the A/C-heat-
er assembly. (23) Disconnect the temperature control cable from
the bottom of the A/C-heater assembly and position
out of the way. (24) Disconnect wiring at the blower motor and
fin-sensing cycling clutch switch electrical connectors. (25) Un-plug the antenna cable from the radio.
(26) Remove the metal (A/C-heater-to-instrument
panel) hanger strap from the upper part of the A/C-
heater assembly. (27) Roll back the floor carpeting from under the
A/C-heater assembly far enough to avoid restricting
unit removal. (28) Remove the A/C-heater assembly through the
opening on the right side of the console, and remove
unit from vehicle. The instrument panel (to the left side of the glove box
opening) must be slightly folded back to remove the
unit from the vehicle. If wrinkles appear in the instru-
ment panel after the unit has been installed, they may
be removed using a heat gun. Refer to Installation AG,
AJ Body for instructions. To install, reverse steps (28) through (13). If wrinkles
have appeared in the instrument panel, apply low heat
from a heat gun over the wrinkled area. Do not
overheat the instrument panel padding or the
surrounding area. Reverse steps (12) through (1). If equipped with A/C,
evacuate and charge the refrigerant system.
HEATER-A/C UNIT RECONDITION
The following operation requires the removal of the
heater-A/C unit assembly from the vehicle. Refer to
Heater-A/C Unit Assembly removal and installation in
this Group.
DISASSEMBLE
(1) Place the heater-A/C unit on a suitable work
surface. (Fig. 1).
(2) Locate and remove one retaining nut from the
blend-air door pivot shaft.
Fig. 7 Cut Line For A/C-heater RemovalÐAG/AJ Body
Fig. 1 Position Heater-A/C Unit for Disassembly andReassembly
Ä HEATING AND AIR CONDITIONING 24 - 63

(3) To remove the top cover from the A/C-heater
case, the crank arm must be removed (Fig. 2).
(4) Disconnect the vacuum lines from the defroster
and panel mode vacuum actuators and position them
out of the way. (5) Remove three heater-A/C unit cover attaching
screws going upward at the defroster outlet chamber. (6) Remove two heater-A/C unit cover attaching
screws going upward at the air inlet plenum. (7) Remove eleven heater-A/C unit cover attaching
screws going downward into the housing. Then lift
the cover from the heater-A/C unit. (Fig. 3).
To reassemble, lower the heater-A/C unit cover
into place. Then guide the panel air mode door pivot
shaft into its socket and reverse the preceding oper-
ation.BLEND-AIR DOOR
REMOVAL AND INSTALLATION
The following operation requires the removal of the
heater-A/C unit assembly from the vehicle. Refer to
Heater-A/C Unit Assembly removal and installation
in this Group. (1) Remove Heater-A/C unit top cover.
(2) Remove the nut from bottom of the blend-air
door pivot shaft and lift the blend-air door from the
heater-A/C unit housing. (Fig. 4).
To install, reverse the preceding operation.
HEATER CORE
REMOVAL AND INSTALLATION
Refer to Heater A/C Unit Recondition in this
Group.
EVAPORATOR COIL
REMOVAL AND INSTALLATION
Refer to Heater A/C Unit Recondition in this
Group.
CONDENSATE DRAIN TUBE
Condensation that accumulates on the bottom of
the evaporator housing is drained from a rubber tube
through the dash panel and on to the ground. This
tube must be kept open to prevent condensate water
from collecting in the bottom of the heater A/C unit
housing. The tapered end of the drain tube is designed to
keep contaminants from entering the heater A/C unit
housing. If the tube is pinched or blocked, condensate
cannot drain, causing water to back up and spill into
Fig. 2 Blend-Air Door Crank Linkage Removal
Fig. 3 Heater-A/C Unit Cover Removal and Installation
Fig. 4 Blend-Air Door Removal and Installation
24 - 64 HEATING AND AIR CONDITIONING Ä

the passenger compartment. It is normal to see con-
densate drainage below the vehicle. If the tube is
damaged, it should be replaced.
REMOVAL AND INSTALLATION
(1) Raise vehicle.
(2) Locate rubber Drain Tube on right side of dash
panel (Fig. 5). (3) Squeeze clamp and remove drain tube.
To install, reverse the preceding operation. Check
the drain tube nipple on the heater-A/C housing for
any obstructions.
Fig. 5 Condensate Water Drain TubeÐTypical
Ä HEATING AND AIR CONDITIONING 24 - 65

tem control. The computer control panel is not ser-
viceable except for the illumination bulbs. For bulb replacement, refer to A/C-Heater Control
Lamp Replacement in Group 8E Instrument Panel. The ATC Computer/Control Panel is located in the
center of the instrument panel above the radio.
REMOVAL AND INSTALLATION
Refer to A/C-Heater control replacement in the
Switch and Panel Component section of Group 8E,
Instrument Panel and Gauges.
POWER MODULE
The power module (PM) (Fig. 4) receives pulse
width modulated logic signals from the computer
control. The PM then supplies varied voltage to the
blower motor ground circuit for different blower
speeds based on the logic signal. The power module
is not serviceable and must be replaced if found to be
defective.
REMOVAL AND INSTALLATION
(1) Disconnect the negative battery cable.
(2) Remove glove box/ash tray assembly. Refer to
Switch and Panel Component Service section of
Group 8E. (3) Remove the four PM attaching screws (Fig. 5).
(4) Disconnect electrical connector.
(4) Gently extract PM (to prevent damage to A/C
evaporator) from A/C-heater housing and remove
from under instrument panel. To install, reverse the preceding operation. Perform
systems check.
AMBIENT TEMPERATURE SENSOR
The ambient air temperature sensor is located in
the A/C housing above the glove box. This is also a
thermistor and will pick up on the environmental
ambient temperature. The computer control uses the
information provided by the ambient sensor to:
² Regulate the low blower speed
² Temperature offsets
² Mode control
The ambient sensor is not serviceable and must be
replaced if found to be defective. The ambient temperature sensor is plugged into a
two wire receptacle in the A/C-heater housing behind
and above the glove box.
REMOVAL AND INSTALLATION
(1) Remove glove box/ash tray assembly.
(2) Locate and remove two attaching screws on
sensor receptacle (Fig. 6). (3) Carefully pull receptacle and sensor from hous-
ing.
CAUTION: It is possible for the sensor to hang up
on the edge of the hole in the A/C-heater housing
assembly during removal. This may cause the sen-
sor to disengage from the receptacle and fall into
the housing.
Fig. 3 ATC Computer ControllerÐAspirator Air Intake
Fig. 4 Power ModuleÐAmbient TemperatureSensorÐFresh/Recirc Door Actuator
Fig. 5 Power Module Removal and Installation
Ä HEATING AND AIR CONDITIONING 24 - 67

(4) Unplug sensor from receptacle.
To install, reverse the preceding operation and
retest system.
FRESH/RECIRC DOOR ACTUATOR
The fresh/recirc door actuator is an electric servo
motor. It (with the use of linkage) mechanically po-
sitions the A/C unit door in the open or closed posi-
tion. Actuation of the servo motor will occur when
drive signals are supplied to the actuator from the
computer control. This actuator does not contain a
feedback strip therefore can not communicate the
fresh/recirc door position back to the computer con-
trol. The fresh/recirc door actuator is not serviceable
and must be replaced if found to be defective. The Fresh/Recirc Door Actuator is located on the
passenger side of the A/C-heater case.
CAUTION: Do not remove any of the motor actua-
tors from the heater-A/C unit assembly with any
electrical power applied. Removal should only be
done with the Ignition OFF. The actuators have no
mechanical stops to limit their travel. If the actuator
rotates and is not connected to the unit assembly,
it will become un-calibrated.
REMOVAL AND INSTALLATION
(1) Remove the glove box/ash tray assembly. Refer
to the Switch and Panel Component Service section
of Group 8E. (2) Remove under panel silencer pad.
(3) Remove the carpeted cover over the air bag
module. (4) Remove the right front kick panel.
(5) Remove metal instrument panel brace (Fig. 7).
(6) Remove two screws mounting the actuator
mounting bracket to the A/C-heater case (Fig. 8). (7) Remove three screws holding the actuator to
the mounting bracket (Fig. 9). CAUTION: Do not allow screw A (Fig. 8) to drop into
A/C-heater housing assembly.
(8) Tilt actuator to release from actuator link. Re-
move actuator from vehicle.
Fig. 9 Actuator Removal and Installation
Fig. 6 Ambient Sensor Removal and InstallationFig. 7 Brace Removal and Installation
Fig. 8 Actuator Mounting Bracket Removal and Installation
24 - 68 HEATING AND AIR CONDITIONING Ä

To install, reverse the preceding operation.
BLEND-AIR DOOR ACTUATOR
The blend-air door actuator (Fig. 10) is an electric
servo motor which mechanically positions the A/C
unit temperature door. Actuation of the servo motor
will occur when drive signals are supplied to the ac-
tuator from the computer control. A feedback strip in
the actuator allows the computer control to know the
exact position of the temperature door at all times.
The blend-air door actuator is not serviceable and
must be replaced if found to be defective.
CAUTION: Do not remove any of the motor actua-
tors from the heater-A/C unit assembly with any
electrical power applied. Removal should only be
done with the Ignition OFF. The actuators have no
mechanical stops to limit their travel. If the actuator
rotates and is not connected to the unit assembly,
it will become un-calibrated.
REMOVAL AND INSTALLATION
The blend-air door actuator is located on the A/C-
heater housing above the floor hump. (1) Remove under panel silencers.
(2) Remove the carpeted cover over the air bag
control module. (3) Remove floor air distribution duct.
(4) Locate and remove three actuator attaching
screws. (5) Lower the blend-air door actuator from A/C-
heater housing while removing actuator from blend-
air door shaft (Fig. 11). (6) Disengage wire connector lock and unplug con-
nector. To install, reverse the preceding operation.
CAUTION: Align the blend-air door shaft to the slot
in the actuator. Be sure the shaft on blend-air door
actuator is properly engaged (when installing) to
prevent damage.
Perform system check.
MODE DOOR ACTUATOR
The mode door actuator is an electric servo motor.
It (with the use of linkages) mechanically positions
the A/C unit panel/bi-level door and the floor/defrost
door. Actuation of the servo motor will occur when
drive signals are supplied to the actuator from the
computer control. This actuator also contains a feed-
back strip which allows the computer control to know
the exact position of the mode door at all times. The
mode door actuator is not serviceable and must be re-
placed if found to be defective. The Mode Door Actuator is located on the side of
the A/C-heater case near the accelerator pedal.
CAUTION: Do not remove any of the motor actua-
tors from the heater-A/C unit assembly with any
electrical power applied. Removal should only be
done with the Ignition OFF. The actuators have no
mechanical stops to limit their travel. If the actuator
rotates and is not connected to the unit assembly,
it will become un-calibrated.
REMOVAL AND INSTALLATION
(1) Remove under panel silencer.
(2) Disconnect electrical connector from actuator.
(3) Pinch and remove the lower plastic clip from
the actuator arm (Fig. 12).
Fig. 10 Blend-Air Door ActuatorÐMode Door ActuatorÐView from bottom of A/C Housing
Figs. 11 Blend-Air Door Actuator Removal andInstallationÐView from bottom of A/C Housing
Ä HEATING AND AIR CONDITIONING 24 - 69

(3) Remove the two aspirator mounting screws.
(4) Disconnect the aspirator intake hose from the
instrument panel. (5) Remove sensor/aspirator and it's wiring har-
ness from vehicle. To install, reverse the preceding operation.
WATER TEMPERATURE SENSOR
The water temperature sensor is located on the
heater core mounting plate (Fig. 17). This is a ther-
mistor which will pick up on the engines coolant
temperature. The computer control uses this informa-
tion to control the cold engine lockout time. The wa-
ter temperature sensor is not serviceable and must
be replaced if found to be defective. The Water Temperature Sensor is located on the
heater hose mounting plate between the heater hose
nipples.
REMOVAL AND INSTALLATION
(1) The A/C-heater housing assembly must be re-
moved for Water Temperature Sensor replacement.
Refer to Heater-A/C Unit Housing Removal and In-
stallationÐAC/AY Body for procedures. (2) Remove sensor mounting screw (Fig. 18).
(3) Disconnect the sensor pigtail wiring harness
from the main wiring harness and remove sensor
from vehicle. To install, reverse the preceding operation. When
tightening the sensor mounting screw, allow the sen-
sor to rotate and contact the upper heater hose nip-
ple. This will aid in sensor efficiency.
SUN SENSOR
The sun sensor (Fig. 19) is mounted on the driver
side of the vehicle on top of the instrument panel.
This is not a thermistor type sensor but rather a
photo diode. For this reason the sun sensor responds
to sun light intensity rather than temperature. It is
used to aid in determining proper mode door position.
The sun sensor is not serviceable and must be re-
placed if found to be defective.
REMOVAL AND INSTALLATION
(1) Carefully pry up the sensor from the instru-
ment panel with a screwdriver (Fig. 20). Place a rag
under the screwdriver to prevent scratching of the
instrument panel. (2) Disconnect the sensor at the wiring harness.
To install, reverse the preceding operation. Snap
the sensor securely to the instrument panel.
Fig. 16 In-Car Temperature Sensor/Aspirator Assembly Removal and Installation
Fig. 17 Water Temperature Sensor
Fig. 18 Water Temperature Sensor Removal and Installation
Ä HEATING AND AIR CONDITIONING 24 - 71

NONÐCOMPUTER AIDED DIAGNOSTIC TESTS
Determine whether the operator complaint is due
to a system failure or improper operation of the ATC
system. The system will to go into a maximum heat
or cooling mode if the operator changes the tempera-
ture setting four or more degrees. Check the following:
² Coolant level
² Refrigerant charge
² Drive belt tension
² Radiator air flow
² Radiator fan operation
² Air suction of In-car Temperature Sensor/Aspirator
To check air suction of the Aspirator, place a small
piece of tissue paper over the Aspirator opening on
the instrument panel. This opening is located to the
right of the steering column. The tissue paper should
cling to the opening if system is functioning properly. Bring the engine to normal operating temperature
and proceed with Computer Aided Diagnostic Proce-
dures. Always test the entire system after each re-
pair has been performed.
COMPUTER AIDED DIAGNOSTIC TESTS
The ATC control has a computer capable of trou-
bleshooting the entire ATC system in approximately
60 seconds. The engine must be running and at nor-
mal operating temperature during the test to provide
hot coolant for the heater. During the ATC Diagnostic Test, the computer will
calibrate the Mode and Blend Door actuators.
CAUTION: Do not remove the actuators from the
heater-A/C unit assembly with power applied. Re-
moval should only be done with the Ignition OFF.
The actuators have no mechanical stops to limit the
travel. If the actuator rotates and is not connected
to the unit assembly, it will become un-calibrated.
The Diagnostic Test is capable of checking all elec-
trical signals between the ATC Control Module, ac-
tuators, sensors and blower control. The Diagnostic Test will display two types of Diag-
nostic trouble Codes (Fig. 21). The Diagnostic Trou-
ble Codes numbered 01 through 22, have been
detected during the Diagnostic Test. Diagnostic Trou-
ble Codes numbered 23 through 28, have been de-
tected during normal ATC operation. Diagnostic
Trouble Codes 23 through 28 would then be stored in
the ATC control computer and are only being re-
trieved during the Diagnostic Test.
For electrical pin numbers, refer to the wiring Pin
out charts on the following pages in this section. (1) Start vehicle and allow engine to warm up.
(2) For two seconds, depress the DEFROST,
FLOOR and MODE buttons at the same time. The
ATC control should begin to flash on and off. (3) During the Diagnostic Test perform the follow-
ing symptom tests: (a) Do all display symbols and indicators illumi-
nate ?
Fig. 19 Sun Sensor
Fig. 20 Sun Sensor Removal
Fig. 21 Automatic Temperature Control Diagnostic Trouble Codes
24 - 72 HEATING AND AIR CONDITIONING Ä

(b) Does the blower motor operate at its highest
speed ? (c) Feel the outlet temperature. Does it get hot
and then cycle cold ? (d) Does the air flow switch from DEFROST out-
lets and then cycle to PANEL outlets?
If you can answer NO to any of these questions,
proceed to step 4, otherwise proceed to step 5. (4) If you answered NO to:
SYMPTOM A
The display symbols and indicators do not illumi-
nate. Diagnostic Trouble Codes are not displayed.
TEST
After self-diagnostic test is complete, select a mode
that will display the malfunction.
ACTION
If the ATC system operates properly, and the dis-
play does not, replace ATC control panel computer.
SYMPTOM B
The blower motor does not operate.
CAUTION: Stay clear of blower motor and power
module (PM) heat sink. Do not run system for more
than 10 minutes with PM removed from A/C unit.
TEST Check all power module and blower motor connec-
tions. Use a voltmeter to test for 12 volts (ignition)
at both ends of the fuse with ignition ON. If fuse is
good, test the green wire at the blower motor connec-
tor for 12 volts (ignition) to body ground. Turn ignition to the ON position.
With the blower motor still connected, check for 12
volts to body ground on the black/tan wire of the
blower motor two way connector. Check for 12 volts at the Power Module pin #4
(BK/TN). Check for continuity from the Power Module pin
#3 (BK) to chassis ground. Replace the Power Module.
ACTION If 12 volts is not detected, repair feed circuit. Refer
to the Front Wheel Drive Car-Wiring Diagrams Ser-
vice Manual. If 12 volts is not detected, repair wires of the
blower motor or replace the blower motor. If 12 volts is not present, repair wire from the
blower motor connector to the Power Module. If circuit is open, repair ground circuit of the Power
Module. Replace the Power Module (power transistor open).
SYMPTOM C
The outlet air temperature does not become hot
and then cycle to cold during self-test operation. Di-
agnostic Trouble Codes are not displayed.
TEST/ACTION
Make sure the blend-air door is properly attached
to the actuator. If cold air is not discharged from the outlets, check
the base A/C refrigerant system. Make sure heating operation works correctly, (wa-
ter level, thermostat, heater hoses, heater core, etc.).
SYMPTOM D
Air does not flow from DEFROST outlets and then
cycle to PANEL outlets during self-test operation.
TEST/ACTION Check linkages from the mode door actuator for
binding. Check for proper door travel in the unit.
(5) The computer will do one of two things:
² Will return to the control settings that were se-
lected before the Diagnostic Test was started. This
means the test is over. If Diagnostic Trouble Codes
did not occur, and answers to questions (a), (b), (c),
and (d) were YES, the entire system is operating cor-
rectly.
² The blower motor will stop and the computer will
flash a Diagnostic Trouble Code number from 01
through 28. Record the number and then depress the
PANEL button to advance to the next test. If the
ATC control flashes one or more codes 23 to 28, the
digits on the display will flash alternating Zeros. If
you do nothing, these codes will remain stored within
the ATC control computer. After all repairs have
been made erase fault codes. Refer to Erasing Diag-
nostic Trouble Codes 23 through 28 from ATC Con-
trol in this section. Repair all Diagnostic Trouble Codes in the order
that they have been indicated, and then retest the
system. If any blend door test fails, all remaining
blend door tests will be skipped. IF any mode door
tests fail, all remaining mode door tests will be
skipped. Diagnostic Test can be stopped at any time by de-
pressing any button other than PANEL.
DIAGNOSTIC TROUBLE CODE DEFINITIONS
Non-computer aided diagnostics should be per-
formed first. Hood of vehicle should be closed during
the diagnostic test to keep engine heat from effecting
the ambient temperature sensor. Also refer to the wiring Pin out charts.
² DIAGNOSTIC TROUBLE CODE 1
Involves the wiring or the ATC control head.
² DIAGNOSTIC TROUBLE CODES 2, 13, 14, 15,
20, and 23
Ä HEATING AND AIR CONDITIONING 24 - 73