Two-Stage Thermostat And Two-Stage Heating; Cooling Mode - Carrier 58MVP Installation, Start-Up, And Operating Instructions Manual

closes to energize the gas valve solenoid GV-M. The gas valve
solenoid GV-M permits gas flow to the burners where it is
ignited. After 5 seconds, the igniter HSI is de-energized and a
2-second Flame-Proving period begins.
If the furnace control CPU selects high-heat operation, the
high-heat gas valve solenoid GV-HI is also energized.
4. Flame-Proving-When burner flame is proved at the flame-
proving sensor electrode FSE, the furnace control CPU begins
the blower-ON delay period and continues to hold the gas
valve GV-M open. If the burner flame is not proved within
two seconds, the control CPU will close the gas valve GV-M,
and the furnace control CPU will repeat the ignition sequence
for up to three more Trials-For-Ignition before going to
Ignition-Lockout. Lockout will be reset automatically after
three hours, by momentarily interrupting 115 vac power to the
furnace, or by interrupting 24 vac power at SEC1 or SEC2 to
the furnace control CPU (not at W/W1, G, R, etc.).
If flame is proved when flame should not be present, the
furnace control CPU will lock out of Gas-Heating mode and
operate the inducer motor IDM on high speed until flame is no
longer proved.
5. Inducer Speed Change-If the cycle starts in low-heat, the
furnace control CPU reduces the inducer speed slightly after
flame sense. If cycle starts in high-heat, the furnace control
CPU increases the inducer speed 15 seconds after flame sense.
The reduction in speed in low-heat is to optimize combustion
for maximum efficiency.
6. Blower-On delay-If the burner flame is proven, the
blower-ON delay for low-heat and high-heat are as follows:
Low-heat-60 seconds after the gas valve GV-M is opened, the
BLWM is turned ON at low-heat airflow.
High-heat-35 seconds after gas valve GV-M is opened, the
BLWM is turned ON at high-heat airflow.
Simultaneously, the humidifier terminal HUM and electronic
air cleaner terminal EAC-1 are energized and remain ener-
gized throughout the heating cycle.
7. Switching From Low- To High- Heat- If the furnace control
CPU switches from low-heat to high-heat, the furnace control
CPU will de-energize the the high-heat pressure switch relay
HPSR to close the NC contact and slowly increase the inducer
motor speed until the high-heat pressure switch HPS closes.
When the high-heat pressure switch HPS closes, the high-heat
gas valve solenoid GV-HI is energized and the inducer motor
RPM is noted by the furnace control CPU. The RPM is used
to evaluate vent system resistance. This evaluation is then
used to determine the required RPM necessary to operate the
inducer motor in high-heat mode. The blower motor BLWM
will transition to high-heat airflow five seconds after the
furnace control CPU switches from low-heat to high-heat.
8. Switching From High- To Low- Heat-The furnace control
CPU will not switch from high-heat to low-heat while the
thermostat R-to-W circuit is closed when using a single-stage
thermostat.
9. Blower-Off delay- When the thermostat is satisfied, the R to
W circuit is opened, de-energizing the gas valve GV-M,
stopping gas flow to the burners, and de-energizing the
humidifier terminal HUM. The inducer motor IDM will
remain energized for a 15-second post-purge period. The
blower motor BLWM and air cleaner terminal EAC-1 will
remain energized at low-heat airflow or transition to low-heat
airflow for 90, 120, 150, or 180 seconds (depending on
selection at blower-OFF delay switches). The furnace control
CPU is factory-set for a 120-second blower-OFF delay.
Step 2—Two-Stage Thermostat and Two-Stage Heating
See Fig. 56 for thermostat connections
NOTE: In this mode, the low-heat only switch SW1-2 must be
ON to select the low-heat only operation mode in response to
closing the thermostat R-to-W1 circuit. Closing the thermostat
R-to-W1-and-W2 circuits always causes high-heat operation, re-
gardless of the setting of the low-heat-only switch.
The wall thermostat "calls for heat", closing the R to W1 circuit for
low-heat or closing the R to W1-and-W2 circuits for high-heat.
The furnace control performs a self-check and verifies the low-
heat and high-heat pressure switch contacts LPS and HPS are
open.
The start-up and shutdown functions and delays described in item
1. above apply to 2-stage heating mode as well, except for
switching from low- to high-heat and vice versa.
1. Switching From Low- To High- Heat-If the thermostat R to
W1 circuit is closed and the R to W2 circuit closes, the furnace
control CPU will de-energize the high-heat pressure switch
relay HPSR to close the NC contact and slowly increase the
inducer motor speed until the high-heat pressure switch HPS
closes. When the high-heat pressure switch closes, the high-
heat gas valve solenoid GV-HI is energized and the inducer
motor RPM is noted by the furnace control CPU. The RPM is
used to evaluate vent system resistance. This evaluation is
then used to determine the required RPM necessary to operate
the inducer motor in high-heat mode. The blower motor
BLWM will transition to high-heat airflow 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 energize the high-heat pressure
switch relay HPSR to open the NC contact and slowly
decrease the inducer motor speed to the required low-heat
RPM. When the high-heat pressure switch HPS opens, the
high-heat gas valve solenoid GV-HI is de-energized. 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 transition to low-heat airflow five seconds after
the R to W2 circuit opens.
Step 3—Cooling Mode
The thermostat "calls for cooling"
1. Single-Speed Cooling
(See Fig. 28 for thermostat connections.)
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 cooling airflow.
Cooling airflow is based on the A/C selection shown in Fig.
58.
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 at cooling airflow for an
additional 90 sec. Jumper Y/Y2 to DHUM to reduce the
cooling off-delay to 5 seconds. (See Fig. 32.)
2. Single-Stage Thermostat and Two-Speed Cooling (Adap-
tive Mode)
(See Fig. 57 for thermostat connections.)
This furnace can operate a two-speed cooling unit with a
single-stage thermostat because the furnace control CPU
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