Carrier 120/C Series Installation, Start-Up, Operating And Service And Maintenance Instructions page 49

2. Cooling Mode
The thermostat "calls for cooling."
a. Single-Speed Cooling
(See Fig. 25, 26, 28, and 30 for thermostat connections)
The thermostat closes the R-to-G-and-Y circuits. The R-to-
Y circuit starts the outdoor unit, and the R-to-G-and-Y/Y2
circuits start the furnace blower motor BLWM on COOL
speed.
The electronic air cleaner terminal EAC-1 is energized with
115 vac when the blower motor BLWM is operating.
When the thermostat is satisfied, the R-to-G-and-Y circuits
are opened. The outdoor unit will stop, and the furnace
blower motor BLWM will continue operating on the
COOL speed for an additional 90 seconds. Jumper Y/Y2 to
DHUM to reduce the cooling off-delay to 5 seconds. (See
Fig. 24.)
b. Two-Speed Cooling
(See Fig. 27, 29, 31, and 32 for thermostat connections.)
The thermostat closes the R-to-G-and-Y1 circuits for
low-cooling or closes the R-to-G-and-Y1-and-Y2 circuits
for high-cooling. The R-to-Y1 circuit starts the outdoor
unit on low-cooling speed, and the R-to-G-and-Y1 circuit
starts the furnace blower motor BLWM on low-cool speed
(same speed as FAN). The R-to-Y1-and-Y2 circuits start
the outdoor unit on high-cooling speed, and the R-to-G-
and-Y/Y2 circuits start the furnace blower motor BLWM
on COOL speed.
The electronic air cleaner terminal EAC-1 is energized
with 115 vac whenever the blower motor BLWM is
operating.
When the thermostat is satisfied, the R-to-G-and-Y1 or
R-to-G-and-Y1 and Y2 circuits are opened. The outdoor
unit stops, and the furnace blower BLWM and electronic
air cleaner terminal EAC-1 will remain energized for an
additional 90 seconds. Jumper Y1 to DHUM to reduce the
cooling off-delay to 5 seconds. (See Fig. 24.)
3. Thermidistat Mode
(See Fig. 26-29 for Thermidistat connections.)
The dehumidification output, DHUM on the Thermidistat
should be connected to the furnace control thermostat terminal
DHUM. When there is a dehumidify demand, the DHUM
input is activated, which means 24 vac signal is removed from
the DHUM input terminal. In other words, the DHUM input
logic is reversed. The DHUM input is turned ON when no
dehumidify demand exists. Once 24 vac is detected by the
furnace control on the DHUM input, the furnace control
operates in Thermidistat mode. If the DHUM input is low for
more than 48 hours, the furnace control reverts back to
non-Thermidistat mode.
The cooling operation described in item 2. above also applies
to operation with a Thermidistat. The exceptions are listed
below:
a. When the R-to-G-and-Y1 circuit is closed and there is a
demand for dehumidification, the furnace blower motor
BLWM will continue running at low-cool speed (same
speed as FAN).
b. When the R-to-G-and-Y/Y2 circuit is closed and there is a
demand for dehumidification, the furnace blower motor
BLWM will drop the blower speed from COOL to HEAT
for a maximum of 10 minutes before reverting back to
COOL speed. If there is still a demand for dehumidification
after 20 minutes, the furnace control CPU will drop the
blower speed back to HEAT speed. This alternating 10-
minute cycle will continue as long as there is a call for
cooling.
c. When the "call for cooling" is satisfied and there is a
demand for dehumidification, the cooling blower-off delay
is decreased from 90 seconds to 5 seconds.
4. Continuous Blower Mode
When the R-to-G circuit is closed by the thermostat, the
blower motor BLWM will operate on continuous-blower
speed (can be adjusted to FAN, HEAT, or COOL speed) at the
thermostat. Factory default is FAN speed. Terminal EAC-1 is
energized as long as the blower motor BLWM is energized.
During a call for heat, the blower BLWM will stop during
igniter warm-up (17 seconds), ignition (7 seconds), and
blower-ON delay (25 seconds), allowing the furnace heat
exchangers to heat up more quickly, then restarts at the end of
the blower-ON delay period at HEAT speed.
In heating, the furnace control CPU will hold the blower
motor BLWM at HEAT speed during the selected blower-OFF
delay period before reverting to continuous-blower speed.
When the thermostat "calls for low-cooling," the blower motor
BLWM will switch to operate at low-cool speed (same speed
as FAN). When the thermostat is satisfied, the blower motor
BLWM will operate an additional 90 seconds on low-cool
speed (same speed as FAN) before reverting back to
continuous-blower speed.
When the thermostat "calls for high-cooling", the blower
motor BLWM will operate at COOL speed. When the ther-
mostat is satisfied, the blower motor BLWM will operate an
additional 90 seconds on COOL speed before reverting back
to continuous-blower speed.
When the R-to-G circuit is opened, the blower motor BLWM
will continue operating for an additional 5 seconds, if no other
function requires blower motor BLWM operation.
Continuous Blower Speed Selection from Thermostat -To
select different continuous-blower speeds from the room
thermostat, momentarily turn off the FAN switch or push-
button on the room thermostat for 1-3 seconds after the blower
motor BLWM is operating. The furnace control CPU will shift
the continuous-blower speed from the factory setting of FAN
to HEAT speed. Momentarily turning off the FAN switch
again at the thermostat will shift the continuous-blower speed
from HEAT to COOL. Repeating the procedure will shift the
continuous-blower speed from COOL to FAN speed. The
selection can be changed as many times as desired and is
stored in the memory to be automatically used following a
power interruption.
5. Heat pump
(See Fig. 28-31 for thermostat connections.)
When installed with a heat pump, the furnace control auto-
matically changes the timing sequence to avoid long blower
off times during demand defrost cycles. When the R-to-
W-and-Y1 or R-to-W-and-Y1-and-G circuits are energized the
furnace control CPU will switch to or turn on the blower
motor BLWM at HEAT speed, and begin a heating cycle. The
blower motor BLWM will remain on until the end of the
prepurge period, then shut off for 24 seconds then come back
on at HEAT speed. When the W input signal disappears, the
furnace control begins a normal inducer post-purge period and
the blower remains running at HEAT speed for the selected
blower-OFF delay period then switches to low-cool speed
(same speed as FAN). If the R-to-W-and-Y1-and-G signals
disappear at the same time, the blower motor BLWM will
remain on for the selected blower-OFF delay period. If the R-
to-W-and-Y1 signals disappear, leaving the G signal, the
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