Cooling Mode; Continuous Blower Mode; Heat Pump Mode; Component Test - Carrier 58MXA Operating And Instruction Manual

air cleaner remains energized 90, 135, 180, or 225 sec
(depending on blower off time selection). Furnace is factory
shipped set for a 135-sec blower off delay.
7. Post purge—Inducer motor remains energized 15 sec after
burners are extinguished.
Step 2—Cooling Mode
When thermostat "calls for cooling," R-G and R-Y circuits close.
R-Y circuit starts outdoor condensing unit, and combined R-Y and
R-G circuit starts furnace blower motor on cooling speed. Elec-
tronic air cleaner EAC-1 terminal is energized with 115v whenever
blower is operating.
When thermostat is satisfied, R-G and R-Y circuits are opened,
furnace blower continues operating on cooling speed for an
additional 90 sec.
Step 3—Continuous Blower Mode
When R-G circuit is made, blower motor operates on heating
speed.
NOTE: Electronic air cleaner EAC-1 terminal is energized with
115v whenever blower is operating.
If a "call for heat" (R-W) occurs while thermostat is in continuous
blower mode, blower stops to allow furnace heat exchangers to
heat up more quickly, then restarts at end of blower on delay
period of 60 sec.
Blower reverts to continuous operation after heating cycle is
completed.
If a "call for cooling" (R-Y) occurs while thermostat is in
continuous blower mode, blower changes from continuous blower
speed (heating speed) to cooling speed.
When thermostat cooling call is satisfied, R-Y opens and blower
operates an additional 90 sec at cooling speed before reverting
back to continuous operation (heating speed).
Step 4—Heat Pump Mode
When installed with a heat pump, furnace control automatically
changes blower on delay timing sequence to avoid no blower
operation time during demand defrost cycles. When R-W and R-Y
or R-W, R-Y, and R-G thermostat inputs are received at the same
time at furnace control center, control starts blower in heating
speed. Then a gas heat mode begins. Blower remains operating at
heating speed for 15 sec or until end of prepurge period, then
blower shuts off until end of ignitor warm up and trial for ignition
periods (a total of 24 sec). Blower restarts at heating speed.
When R-W thermostat call disappears, control completes inducer
post-purge period (15 sec) and changes to cooling speed after a
2-sec delay.
If R-W, R-Y, and R-G thermostat signals should disappear
simultaneously, blower remains on for selected heating blower off
delay period (90, 135, 180, or 225 sec), and the inducer goes
through 15 sec post-purge period. If R-W and R-Y thermostat
signals should disappear, leaving R-G thermostat signal, blower
remains on in heating speed and inducer remains on for 15 sec to
complete post-purge period.
Control initiates a 90-sec blower only on period before starting
another heat pump cycle if there is a power interruption. Anytime
control senses false flame, control locks out of heating mode. This
reaction occurs because control ignores W input due to false flame
signal and, as a result, sees only Y input and goes into cooling
mode blower off delay. All other control functions remain in
standard format.
NOTE: EAC-1 terminal is energized whenever blower operates.
HUM terminal is only energized when gas valve is energized.
→
Step 5—Component Test
COMPONENT TEST SEQUENCE
NOTE: All components are functionally operated except the gas
valve.
When component test is initiated, the following sequence of events
occurs:
1. LED flashes a fault code 4 times.
2. Inducer motor starts and continues to run for remainder of

component test.

3. Hot surface ignitor is energized for 15 sec, then de-energized.
4. Main blower operates at cooling speed for 10 sec, then turns
off.
5. Main blower operates at heating speed for 10 sec, then turns
off.
6. Inducer motor stops.
Component test can be initiated by one of the following proce-
dures.
INITIATING COMPONENT TEST BY REMOVING MAIN
LIMIT SWITCH WIRE
NOTE: NO thermostat signal may be present at control center
and all blower time delay off periods must be completed.
1. Leave 115-v power to furnace turned on.
2. Remove main furnace door.
3. Look into blower access panel sight glass for current LED
status.
NOTE: Leave blower access panel installed to maintain power to
control center to view current LED status.
4. BRIEFLY remove either wire from the main limit switch until
the LED goes out, then reconnect it.
Make sure limit switch wire does not contact any metallic
component such as the gas valve. If wire is shorted, 3-amp
fuse on control center will blow.
NOTE: If wire to main limit is disconnected longer than 4 sec, the
control senses limit circuit is open. Main blower will start and fault
retrieval request will be ignored.
5. When above items have been completed, the component test
sequence will occur as described in the Component Test
Sequence section above.
NOTE: Be sure to record the fault code which is flashed 4 times
at start of component test for further troubleshooting.
6. After component test is completed and LED is ON continu-
ously indicating the furnace is ready to operate when a signal
from the thermostat is received, replace main furnace door.
INITIATING COMPONENT TEST BY JUMPERING CON-
TROL TEST TERMINAL
1. Remove main furnace door.
2. Remove blower access panel.
3. Manually close blower access panel door switch. Use a piece
of tape to hold switch closed.
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