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Table 3. Heat Pump Applications (W8900B).
a
AUX controls the auxiliary heat like W2, and allows additional stages of auxiliary heat with outdoor thermostats while maintain-
ing the proper second stage anticipation.
b
For systems without 2nd stage heat, configure W2 to No.
c
For systems requiring separate W1 and Y1 terminals for proper heat pump operation, refer to Fig. 18 and 19.
d
Replace existing sensor with C7089A Outdoor Sensor.
W8900B Terminal
Designations
Function
Existing Thermostat
Designations
(Standard)
Existing Thermostat
Designations
(Customer Specials)
1 PC8900A Control Panel — —
2 PC8900A Control Panel — —
3 PC8900A Control Panel — —
4 PC8900A Control Panel — —
AUX
a
Stage-3 heat control (strip heat) W3 —
B Heating, changeover valve B —
C 24 Vac transformer common C X,B
CO
2
Carbon dioxide monitor — —
E Emergency heat relay E K
VNT VNT relay — —
G Fan relay G F
GND Ground — —
L System monitor L L
O Cooling, changeover valve O R
R 24 Vac system transformer R V
S, S1 Remote Air Temperature Sensor — —
T, T1 Discharge Air Temperature Sensor — —
W2
b
Stage-2 heat control (compressor) W2 H2,Y,R4
Y1/W1
c
Compressor contactor — RS
Y1/W1
c
Compressor contactor Y M
Y1/W1
c
Stage-1 cool control Y1 C1,M
Y1/W1
c
Stage-1 heat control W1 H1,R3
Y2 Stage-2 cool control Y2 C2
None Clogged filter switch or common connection X X1,X2,C
None Defrost — P
None HSII Control Panel — L,C,H
None LEDs — A,A1,A2,Z,C,L
None LO and HI speed fan relays — R1,R2
None Momentary circuit, changeover — O
None Outdoor thermistor T A
Out
d
External temperature readout, T relay — —
