Carrier BASE 25HBR Installation Instructions Manual page 9

HP THERMOSTAT
24 VAC HOT R
24 VAC COM C
W2
HEAT STAGE 2
COOL/HEAT
Y
STAGE 1
G
INDOOR FAN
O
RVS COOLING
EMERGENCY
E
*
HEAT
LEGEND
24-V FACTORY WIRING
24-V FIELD WIRING
FIELD SPLICE CONNECTION
ODT
OUTDOOR THERMOSTAT
EMERGENCY HEAT RELAY
EHR
SHR SUPPLEMENTAL HEAT RELAY
Fig. 10 --- Generic Wiring Diagrams
(See Thermostat Installation Instructions for specific unit
combinations)
Sequence of Operation
Turn on power to indoor and outdoor units. Transformer is
energized.
Cooling
On a call for cooling, thermostat makes circuits R- -O and R- -Y,
and R- -G. Circuit R- -O energizes reversing valve, switching it to
cooling position. Circuit R- -Y energizes contactor, starting
outdoor fan motor and compressor circuit. R- -G energizes indoor
unit blower relay, starting indoor blower motor on high speed.
When thermostat is satisfied, its contacts open, de- -energizing
contactor and blower relay. Compressor and motors should stop.
NOTE: If indoor unit is equipped with a time- -delay relay
circuit, the indoor blower will run an additional 90 seconds to
increase system efficiency.
HEAT
TYPICAL
PUMP
FAN COIL
R
R
C
C
*
W2
W2
*
E
Y
*
W3
G
O
IF AVAILABLE
A02325 / A97413
Heating
On a call for heating, thermostat makes circuits R- -Y and R- -G.
Circuit R- -Y energizes contactor, starting outdoor fan motor and
compressor. Circuit R- -G energizes indoor blower relay, starting
blower motor on high speed.
Should temperature continue to fall, R- -W2 is made through
second- -stage room thermostat. Circuit R- -W2 energizes a relay,
bringing on first bank of supplemental electric heat and providing
electrical potential to second heater relay (if used). If outdoor
temperature falls below setting of outdoor thermostat (field
installed option), contacts close to complete circuit and bring on
second bank of supplemental electric heat.
When thermostat is satisfied, its contacts open, de- -energizing
contactor and relay. All heaters and motors should stop.
Defrost
The defrost control is a time/temperature control which includes a
field selectable (quick- -connects located at board edge) time
period between defrost cycles (30, 60, or 90 minutes), factory set
to 90 minutes.
The electronic defrost timer sequence is enabled when the T1
input on the board is energized. The timer starts only when the
defrost thermostat is closed and the contactor is energized.
Defrost mode is identical to cooling mode except that outdoor fan
motor stops and second- -stage heat is turned on to continue
warming conditioned spaces.
To initiate defrost, the defrost thermostat must be closed. This can
be accomplished as follows:
1. Turn off power to outdoor unit.
2. Disconnect outdoor fan motor lead from OF2 on control
board, see Fig. 11. Tape lead to prevent grounding.
3. Restart unit in heating mode, allowing frost to accumulate
on outdoor coil.
4. After a few minutes in heating mode, liquid line
temperature should drop below closing point of defrost
thermostat (approximately 30°F).
5. Short between speedup terminals with a flat- -blade
screwdriver. This reduces the timing sequence to 1/256th
of original time. (See Table 4.)
6. When you hear reversing valve change position, remove
screwdriver immediately; otherwise, control will terminate
normal 10- -minute defrost cycle in approximately 2
seconds.
NOTE: Length of defrost cycle is dependent upon length of time
it takes to remove screwdriver from test pins after reversing valve
has shifted.
7. Unit will remain in defrost for remainder of defrost cycle
time or until defrost thermostat reopens at approximately
65°F coil temperature of liquid line.
8. Turn off power to outdoor unit and reconnect fan motor
lead to OF2 on control board.
9