Carrier 58MVP - Manual (Page 3)

In emergency heat mode, the normal heat mode outlined in
Heating Mode section is not followed. The following sequence
will occur:
When 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 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 IMMEDI-
ATELY.
5. Ignitor warm up—The HSI is energized for a 17 sec
warm-up period after prepurge period is completed.
6. Ignition sequence—After HSI warm-up period has com-
pleted, the gas valve is energized, permitting gas flow to
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, control center
holds gas valve open. If burner flame is not sensed, control
center de-energizes gas valve and ignition sequence is re-
peated.
NOTE: Ignition sequence repeats 3 additional times before lock-
out occurs. Lockout automatically resets after 3 hr, or can be
manually reset by turning 115-v or 24-v power off (not at
thermostat) for 3 sec minimum, then turning on again. Fault codes
will not flash in emergency heat mode.
8. Blower off delay—When thermostat is satisfied, the R-W/W1
signal is terminated, de-energizing gas valve (stopping gas
flow to burners) and HUM terminal is de-energized. In
addition, blower stops immediately.
9. Post purge—Post purge does NOT occur. The inducer stops
immediately.
Step 5—Cooling Mode
When thermostat calls for cooling, the R-G and R-Y/Y2 circuits
close.
1. Cooling unit—The cooling unit starts when thermostat R-Y
signal is received.
2. Blower on—The control center starts 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 resistance of the conditioned air duct system.
The microprocessor then determines blower RPM required to
provide selected cooling airflow.
NOTE: In cooling mode, the microprocessor adjusts blower RPM
to operate at 400 CFM per ton as selected on the A/C setup
switches. Airflow will be reduced to 340 or 315 CFM per ton,
depending on board style (See Fig. 1), when a dehumidification
demand exists. See Air Conditioning Setup Switches section in
Installation, Start-Up and Operating Instructions for details. There
is also a chart on schematic in Appendix A.
NOTE: If Y/Y2 thermostat lead is not connected to furnace
control center, blower motor operates in continuous fan speed and
indoor coil freeze-up may occur.
3. Electronic Air Cleaner—The EAC-1 terminal is energized
whenever blower operates.
4. Cooling unit—The cooling unit stops when thermostat R-Y
signal is terminated.
5. Blower off delay—When thermostat is satisfied, the R-Y/Y2
and R-G signals are terminated, and blower remains operating
for 90 sec. On newer style control boards (See Fig. 1), the
blower airflow will drop by 21 percent during the off-delay
period when the DE jumper is connected. The DE jumper is
only removed to enable the DEHUM input for use with a
thermidistat or humidistat for dehumidification purposes.
Step 6—Heat Pump Mode
When furnace is operating in heat pump heating mode, R-Y/Y2
and R-G circuits are closed energizing heat pump, and blower
operates at cooling speed. When heat pump defrost is required,
R-W/W1 circuits close starting gas heat cycle, and blower adjusts
to low-heat speed.
1. Prepurge period—The inducer motor is turned on and slowly
comes up to speed. When low-pressure switch closes, inducer
motor RPM is noted by microprocessor, and a 25 sec prepurge
period begins. The RPM is used to evaluate vent system
resistance. This evaluation is then used to determine required
RPM necessary to operate inducer in low-heat mode.
NOTE: The heat cycle can start in either high or low heat. If a
high-heat cycle is initiated, inducer continues increasing its speed
after low-pressure switch closes. When high-pressure switch
closes, inducer motor RPM is noted by microprocessor before the
25 sec prepurge period begins. The RPM is used to evaluate vent
system resistance. This evaluation is used to determine required
RPM necessary to operate inducer in high-heat mode.
2. Humidifier—The HUM terminal is energized whenever in-
ducer prepurge period is completed.
3. Ignitor warm up—After prepurge period, HSI is energized
for 17 sec.
4. Ignition sequence—After HSI warm-up period is completed,
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.
5. Flame sensing—When burner flame is sensed, control center
holds gas valve open.
If burner flame is not sensed, control center de-energizes gas
valve and ignition sequence is repeated.
6. Blower off period—Ten sec after gas valve is energized, the
blower stops for 25 sec to allow heat exchangers to warm up.
7. Blower on delay—After blower off period, blower starts.
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 resistance of the conditioned air
duct system. The microprocessor then determines blower RPM
required to provide proper airflow for heating mode.
8. Electronic Air Cleaner—The EAC-1 terminal is energized
whenever blower operates.
9. Inducer speed reduction—If cycle starts in low heat, inducer
speed reduces slightly after the flame sense. If cycle starts in
high heat, inducer speed increases 15 sec after flame sense.
The reduction in speed in low heat is to optimize combustion
for maximum efficiency.
10. Call for heat terminated—When the call for heat is satisfied,
the R-W/W1 signal is terminated, de-energizing gas valve
(stopping gas flow to burners) and HUM terminal is de-
energized.
a. R-W/W1 signal terminated with R-Y/Y2 and R-G still
present—The blower changes its speed to cooling RPM.
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