68-0173—3 14
W8900B Hookup Diagrams

Fig. 16. Hookup diagram for 2-stage heat/1-stage cool in heat pump system.

S1
S
T1
T
OUT
OUT
LED
O/B
G
Y2
Y1/W1
E
AUX
W2
1
2
3
4
GND
C
R
RH
HUM
HUM
VNT
VNT

W8900B

L1
(HOT)
L2
1
3
2
4
1
2
3
4
5
6
7
7
5
6
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
JUMPER R TO RH.
DURING INSTALLER SETUP, CONFIGURE PC8900 FOR HUMIDITY CONTROL IN HEATING MODE
(HUMIDIFIER) OR COOLING MODE (DEHUMIDIFIER).
W8900 ALLOWS CONNECTION OF A CO MONITOR WITH UNCOMMITTED CONTACTS.
CONFIGURE PC8900 FOR CHANGEOVER IN HEATING MODE OR COOLING MODE.
IF SEPARATE Y1 AND W1 TERMINALS ARE REQUIRED, REFER TO FIGURES 18 AND 19.
SEE VENTILATION INSTRUCTIONS FOR WIRING.
GROUNDING THE GND TERMINAL IS NOT RECOMMENDED.
CONNECTION FOR CM8900A REMOTE COMMUNICATIONS MODULE.
CONFIGURE PC8900 FOR NO CONNECTION TO TERMINALS Y2, E, AUX AND W2 FOR
SINGLE-STAGE HEAT PUMP SYSTEM.
CHANGEOVER
RELAY
AUXILIARY
HEAT RELAY

PC8900

1
2
3
4
CO
2
MONITOR
M4483D
FAN RELAY
EMERGENCY
HEAT RELAY
COMPRESSOR
CONTACTOR
COMPRESSOR
MONITOR
HUMIDIFIER OR
DEHUMIDIFIER
EQUIPMENT
VENTILATION
EQUIPMENT
SYSTEM
TRANSFORMER
C7189A REMOTE AIR
TEMPERATURE SENSOR
C7100 DISCHARGE AIR
TEMPERATURE SENSOR
C7089A OUTDOOR AIR
TEMPERATURE SENSOR
CO
2
8
9
10
8
9
10
L
2