Heat Mode-Two Stage; Emergency Heat Mode; Cooling Mode - Carrier 58MVP080 Installation, Start-Up, And Operating Instructions Manual

NOTE: The initial heat mode after 115-v or 24-v power interrup-
tion will be LOW HEAT. Low heat remains energized for 16
minutes before high heat is initiated, providing the thermostat is
still "calling for heat."
After the initial cycle, the microprocessor evaluates the length of
the low- and high-heat operating times and calculates the optimum
length of low and high heat for the next heat cycle. This
accommodates the heat load requirement seen as a result of the
thermostat operating time.
5. Flame sensing—When burner flame is sensed, the control
center holds gas valve open and begins the blower on delay
period.
NOTE: Ignition sequence repeats 3 additional times before a
lockout occurs. Lockout automatically resets after 3 hrs, or can be
manually reset by turning 115v or 24v off (not at thermostat) for
3 sec minimum, then turning on again.
6. Inducer speed reduction—If cycle starts in low heat, the
inducer speed reduces slightly after the flame sense, or 15 sec
after flame sense if cycle starts in high heat. The reduction in
speed is to optimize combustion for maximum efficiency.
7. Blower on delay—The blower starts 60 sec after flame sense
if cycle started in low heat or 35 sec after flame sense if cycle
started in high heat.
NOTE: The blower starts at approximately 400-500 RPM. After
20 sec, the motor is turned off for 1/10 of a sec where a coast down
calibration is done to evaluate the resistance of the conditioned air
duct system. The microprocessor then determines the blower RPM
to provide the proper airflow for heating mode.
8. Electronic Air Cleaner—The EAC-1 terminal is energized
whenever the blower operates.
9. Blower off delay—When the thermostat is satisfied, the R-W
signal is terminated, de-energizing the gas valve (stopping gas
flow to the burners) and the HUM terminal is de-energized.
The blower reduces its speed to the low-heat RPM. The
blower and EAC remain operating 90, 135, 180, or 225 sec
(depending on blower off time selection). The furnace is
factory set for a 90 sec blower off delay.
10. Post purge—The inducer continues operating for 15 sec after
the gas valve is de-energized.
Step 3—Heat Mode—Two Stage
The control center provides 2-stage heating using a single-stage
thermostat. The control center maximizes comfort while optimiz-
ing efficiency to meet the demands of the conditioned area when
a thermostat R-W/W1 signal is received.
If thermostat control over the control center microprocessor
operation is desired, a 2-stage thermostat can be used. When the
control center receives a thermostat R-W/W1 and R-W2 signal,
high heat is energized and when R-W/W1 signal is received, low
heat is energized. This method overrides the microprocessor
control of high or low heat.
NOTE: When using 2-stage thermostat operation with R-W/W1
and R-W2 signals, setup switch SW-2 MUST be in ON position.
The heat cycle operates as stated above.
To allow for greater comfort, a 2-stage thermostat control is
recommended when zone systems are used.
Step 4—Emergency Heat Mode
NOTE: The furnace should not be operated in emergency heat
mode for extended periods of time. Operation is only recom-
mended to provide heat until replacement components can be
obtained or fault resolved.
In this mode, the microprocessor is bypassed and the motors
operate at full speed with high-heat operation. The heat exchang-
ers, motors, and electronics can be overstressed and may reduce
the life of the components if operated for an extended period.
NOTE: No safeties are bypassed when using emergency heat
mode.
Emergency heat mode activates automatically if the control
center's microprocessor has failed and a "call for heat" is received
from the thermostat.
Emergency heat mode can also be selected using setup switch
SW-4. SW-4 should be used when a fault condition exists or
difficult to resolve problems occur. This allows heating until the
fault can be corrected.
In emergency heat mode, the normal heat mode outlined above is
not followed. The following sequence will occur:
When the thermostat "calls for heat", the R-W/W-1 circuits close.
1. Prepurge period—The inducer motor is turned on IMMEDI-
ATELY operating at maximum speed, closing the low- and
high-pressure switches. Prepurge begins 25 sec after high-
pressure switch closes.
2. Blower on—The blower motor is turned on IMMEDIATELY
and slowly increases to maximum speed as soon as a "call for
heat" is received. No blower calibration occurs.
3. Electronic Air Cleaner—The EAC-1 terminal does not
operate in emergency heat mode.
4. Humidifier—The HUM terminal is energized when the
inducer prepurge period is completed.
5. Ignitor warm up—The HSI is energized for a 17 sec
warm-up period after the prepurge period is completed.
6. Ignition sequence—After the HSI warm-up period has com-
pleted, the gas valve is energized, permitting gas flow to the
burners where it is ignited. After 5 sec, the HSI is de-energized
and a 2-sec flame-sensing period begins.
NOTE: Emergency heat mode only operates in high heat.
7. Flame sensing—When burner flame is sensed, the control
center holds the gas valve open. If burner flame is not sensed,
the control center de-energizes the gas valve and the ignition
sequence is repeated.
8. Blower off delay—When the thermostat is satisfied, the
R-W/W1 signal is terminated, de-energizing the gas valve
(stopping gas flow to the burners) and the HUM terminal is
de-energized. In addition, the blower stops immediately.
9. Post purge—Post purge does NOT occur. The inducer stops
immediately.
Step 5—Cooling Mode
When the thermostat "calls for cooling," the R-G and R-Y/Y2
circuits close.
1. Cooling unit—The cooling unit starts when the thermostat
R-Y signal is received.
2. Blower on—The control center starts the blower immediately
when it receives an R-Y/Y2 and R-G signal. The blower starts
at approximately 400-500 RPM. After 20 sec, the blower is
turned off for 1/10 of a sec where a coast down calibration is
done to evaluate the resistance of the conditioned air duct
system. The microprocessor then determines the blower RPM
to provide the selected cooling airflow.
NOTE: In the cooling mode, the microprocessor adjusts the
blower RPM to operate at 400 CFM per ton as selected on the A/C
setup switches.
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