Cooling Mode; Thermidistat Mode - Carrier 58MTB Installation, Start-Up, And Operating Instructions Manual

the high-heat gas valve solenoid GV-HI is energized. The
blower motor BLWM will switch to HI HEAT speed five
seconds after the R to W2 circuit closes.
2. Switching From High- To Low- Heat- If the thermostat R to
W2 circuit opens, and the R to W1 circuit remains closed, the
furnace control CPU will switch the inducer motor IDM speed
from high to low. The high-heat pressure switch relay HPSR
is energized to open the NC contact and de-energize the
high-heat gas valve solenoid GV-HI. When the inducer motor
IDM reduces pressure sufficiently, the high-heat pressure
switch HPS will open. The gas valve solenoid GV-M will
remain energized as long as the low-heat pressure switch LPS
remains closed. The blower motor BLWM will switch to LO
HEAT speed five seconds after the R to W2 circuit opens.

COOLING MODE

The thermostat "calls for cooling"
1. Single-Speed Cooling
(See Fig. 31 or 32 and 50A, C, or E for thermostat connec-
tions.)
The thermostat closes R-to-G-and-Y circuits. The R-to-Y
circuit starts the outdoor unit, and 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-v when 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 furnace blower motor
BLWM will continue operating on COOL speed for an
additional 90 sec. Jumper Y/Y2 to DHUM to reduce the
cooling off-delay to 5 seconds. (See Fig. 37.)
2. Two-Speed Cooling and Single-Stage Thermostat
(Adaptive Mode)
(See Fig. 31 and 50A-H for thermostat connections.)
This furnace can operate a two-speed cooling unit with a
single-stage thermostat because the furnace control CPU
includes a programmed adaptive sequence of controlled
operation, which selects low-cooling or high-cooling op-
eration. This selection is based upon the stored history of
the length of previous cooling period of the single-stage
thermostat.
NOTE: The air conditioning relay disable jumper ACRDJ must
be connected to enable the adaptive cooling mode in response to a
call for cooling. (See Fig. 32.) When in place the furnace control
CPU can turn on the air conditioning relay ACR to energize the
Y/Y2 terminal and switch the outdoor unit to high-cooling.
The furnace control CPU can start up the cooling unit in
either low- or high-cooling. If starting up in low-cooling,
the furnace control CPU determines the low-cooling on-
time (from 0 to 20 minutes) which is permitted before
switching to high-cooling.
If the power is interrupted, the stored history is erased and
the furnace control CPU will select low-cooling for up to
20 minutes and then energize the air conditioning relay
ACR to energize the Y/Y2 terminal and switch the outdoor
unit to high-cooling, as long as the thermostat continues to
call for cooling. Subsequent selection is based on stored
history of the thermostat cycle times.
The wall thermostat "calls for cooling", closing the R to
G-and-Y circuits. The R to Y1 circuit starts the outdoor unit
on low-cooling speed, and the R to G-and-Y1 circuits starts
the furnace blower motor BLWM at low-cool speed (same
speed as LO HEAT).
If the furnace control CPU switches from low-cooling to
high-cooling, the furnace control CPU will energize the air
conditioning relay ACR. When the air conditioning relay
ACR is energized the R to Y1-and-Y2 circuits switch the
outdoor unit to high-cooling speed, and the R to G-and-
Y1-and-Y/Y2 circuits switch the furnace blower motor
BLWM to COOL speed.
NOTE: When transitioning from low-cooling to high-cooling the
outdoor unit compressor will shut down for 1 minute while the
BLWM continues to run at low-cool speed (same speed as
LO-HEAT) until the outdoor unit compressor comes back on at
high 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-Y circuit
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. 37.)
3. Two-Speed Cooling and Two-Stage Thermostat
(See Fig. 32 and Fig. 50A-G for thermostat connections)
NOTE: The ACRDJ must be disconnected to allow thermostat
control of the outdoor unit staging. (See Fig. 37.)
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 LO HEAT).
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. 37.)

THERMIDISTAT MODE

(See Fig. 50A-D 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 or OFF for more than 48 hours, the furnace
control reverts back to non-Thermidistat mode.
The cooling operation described 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 LO HEAT).
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