Carrier 58HDX - SEQUENCE OF OPERATION & DIAGNOSTICS

ELECTRICAL
HAZARD
SHOCK, FIRE OR EXPLOSION
Failure to follow this warning could result in personal injury,
death, and/or property damage.
Before servicing, disconnect all electrical power to furnace.
Lockout and tag with appropriate label.
When servicing controls, label all wires prior to disconnecting.
Reconnect wires correctly.
Verify proper operation after servicing.
See “User’s Information Manual” and the “Service
Manual”.
SEQUENCE OF OPERATION
& DIAGNOSTICS
Following is the normal operating sequence:
Cooling (Y) Request:
24VAC signals applied to Y & G terminals of FCB (furnace
control board)
¢ Cool motor speed is energized after 5 second Cool Fan On
Delay time.
Y & G signals removed from FCB
¢ Cool motor speed is de-energized after 90 second Cool Fan
Off Delay time.
Continuous Circulating Fan (G) Request:
¢ 24 VAC signal is applied to G terminal of the FCB.
¢ Heat motor speed is energized without delay.
¢ Gsignal removed from FCB.
¢ Heat motor speed is de-energized after 5 second delay.
NOTE:
(1.) Furnace de-energizes the fan during the heat ex-
changer warm-up period on a call for Heating
that occurs during a G request unless a blower
motor lead is connected to the Cont terminal on
the FCB, in which case see NOTE 2).
(2.) Heating or Cooling requests received during a Fan
request cause the fan speed to change to the ap-
propriate heat or cool speed after the Fan on
Delay time expires. The fan returns to continuous
circulating speed after the selected Fan Off Delay
time expires following loss of the Heating or
Cooling request.
Continuous Circulating Fan Hard- Wired
(Cont) Request
Field selected low speed motor tap installed on “CONT”
terminal.
¢ Low speed is energized when power applied to furnace.
Operates at this speed continuously while there are no other
blower demands from furnace control. Fan demands from
furnace control for heat, cool or “G” will override hard-wired
speed tap.
NOTE: EAC is NOT active for hard-wired mode but IS active
for fan demands from furnace control for heat, cool and “G”.
Heating (W) Request:
Heating (W) Request:
¢ 24 VAC signal applied to W terminal of FCB.
¢ Inducer motor turns on and the pressure switch(es) close(s)
¢ Following a 15 second prepurge delay, after the pressure
switches closes, the igniter begins a 17 second warm-up.
¢ The gas valve is energized, the main burners light and flame is
sensed.
¢ The igniter is de-energized after the main burners ignite.
¢ FCB will delay blower operation for the 30 seconds timed from
the opening of the gas valve.
¢ W signal removed from FCB.
¢ The gas valve de-energizes and the main burners go out.
¢ The inducer runs for a 15 second postpurge period.
¢ The fan stays at Heat speed.
¢ The fan de-energizes after the selected Heat Fan Off Delay
time expires, timed from the gas valve de-energizing.
HUMIDIFIER - The 24V HUM is energized when the pressure
switch closes on a call for heat. The 115V HUM (called HUM on
Control) is energized when the inducer is energized.
ELECTRONIC AIR CLEANER - EAC is energized when there
is a blower speed call. It is NOT energized when blower operates
in the hard-wired continuous fan mode.
NOTE: If a new Heating request arrives while the control is
waiting in the Heat Fan Off Delay time, the FCB will wait for the
selected Heat Fan Off Delay then start a new heating cycle as
long as the heat call remains.
Heating Request with Gas Shut Off:
24 VAC signal applied to W terminal of FCB.
The FCB will attempt 4 cycles for ignition then go to soft lockout
for 3 hours then try for ignition again as long as the heat call
remains. Power reset will clear lockout.
¢ Inducer motor turns on
¢ Following a 15 second prepurge delay, the igniter begins warm
up.
¢ The igniter glows red-hot for 22 seconds, then turns off. The
FCB flashes error code 6.
¢ The igniter stays off for 17 seconds, then begins to warm up
again.
¢ The igniter glows red hot for 22 seconds then turns off. The
FCB continues flashing error code 6.
¢ The igniter stays off for 17 seconds, then begins to warm up
again.
¢ The igniter glows red hot for 22 seconds then turns off. The
FCB continues flashing error code 6.
¢ The igniter stays off for 17 seconds, then begins to warm up
again.
¢ The igniter glows red hot for 22 seconds then turns off. The
FCB proceeds to soft lockout and stops flashing error code 6
and begins flashing error code 6 + 1.
¢ The inducer motor de-energizes after a 15 second post purge.