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System 1 Low Pressure Switch
J4-5
= +5 VDC regulated supply to LP switch.
J4-10 = input signal to the microboard. 0 VDC = open
switch / +5 VDC = closed switch.
J4-2
= drain (shield connection = 0 VDC)
System 2 Low Pressure Switch
J7-5
= +5 VDC regulated supply to LP switch.
J7-10 = input signal to the microboard. 0 VDC = open
switch / +5 VDC = closed switch.
J7-2
= drain (shield connection = 0 VDC)
DIGITAL OUTPUTS
Refer to the unit wiring diagram and Table 42. The digital
outputs are located on TB3, TB4, and TB5 of the
microboard. ALL OUTPUTS ARE 120 VAC with the ex-
ception of TB5-3 to TB5-4. TB5-3 to TB5-4 are the con-
tacts that can be used for an evaporator blower start sig-
nal (refer to Evaporator Control Contacts in section on
Unit Controls). The voltage applied to either of these ter-
minals would be determined by field wiring.
Each output is controlled by the microprocessor by
switching 120 VAC to the respective output connection
energizing contactors, evap. heater, and solenoids ac-
cording to the operating sequence.
120 VAC is supplied to the microboard via connections
at TB3-1, TB3-7, TB4-3, and TB4-7. Figure 14 illustrates
the relay contact architecture on the microboard.
KEYPAD
The operator keypad is connected to the microboard by
a ribbon cable, which is connected to J2 on the
microboard.
The integrity of a specific "button" on the keypad can be
verified by doing a continuity check across two specific
points (or pins), that represent one of twelve "buttons" on
the keypad.
Table 34 lists the key/pin assignments for the keypad.
Power to the microboard must be turned off, and
the ribbon cable disconnected from the microboard
prior to conducting the tests, or component dam-
age may result.
After the ribbon cable is disconnected from microboard,
ohmmeter leads are connected to the pins representing
the specific "button" to be tested. After connecting the
meter leads, the "button" being checked is pressed and
a reading of zero ohms should be observed. After re-
YORK INTERNATIONAL
FIG. 14 – MICROBOARD RELAY CONTACT
ARCHITECTURE
leasing the "button", the resistance value should be infi-
nite (open circuit).
Pin 1 is usually identified by a stripe on
the ribbon cable.
TABLE 34 – KEYPAD PIN ASSIGNMENT MATRIX
KEYPAD
STATUS
OPER DATA
PRINT
HISTORY
UP ARROW
DOWN ARROW
ENTER/ADV
COOLING SETPOINTS
SCHEDULE/ADVANCE DAY
PROGRAM
OPTIONS
CLOCK
FORM 150.63-NM2
LD03842
4
PIN CONNECTIONS
1 TO 5
1 TO 7
1 TO 6
1 TO 8
2 TO 5
2 TO 7
2 TO 6
2 TO 8
3 TO 5
3 TO 7
3 TO 6
3 TO 8
137
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