Sequence Of Operation; Heating Mode; Cooling Mode; Continuous Blower Mode - Carrier 58GFA Installation, Starting-Up And Operation Manual

This furnace is equipped with a fuse link in the gas control
area. The fuse link will open and shut off power to the gas
valve if a flame rollout or overheating condition occurs in the
gas control area. DO NOT bypass the fuse link. Call your
service dealer to correct inadequate combustion-air supply
problem and replace fuse link.
Before operating the furnace, check each manual reset switch for
continuity. If necessary, press the button to reset the switch.
The blower compartment door must be in place to complete the
115-v circuit to the furnace.
SEQUENCE OF OPERATION — Using the schematic diagram
show in Fig. 10, follow the sequence of operation through the
different modes.
NOTE: When the blower door is in place, 115v is supplied
through blower door interlock switch ILK to heating fan relay
HFR, induced draft relay IDR, and transformer TRAN. Trans-
former TRAN energizes the safety circuit containing fuse link FL
and limit switch LS to energize R.
The furnace pilot must be lit so the thermocouple energizes the
thermal magnet circuit of gas valve GV, which permits gas flow to
the remaining portion of the valve.

1. Heating mode

a. When the wall thermostat "calls for heat" the R-W circuit
closes. This closed circuit supplies power to the 24-v safety
circuit containing automatic reset limit switch LS and fuse
link FL.
b. The inducer-motor relay coil IDR is energized. Inducer
motor relay contacts in the 115-v circuit close, starting
inducer motor IDM. Simultaneously, another set of con-
tacts in inducer-motor relay IDR close in the 24-v circuit
and lock-in until the R-W circuit or safety opens.
c. As inducer motor IDM comes up to speed, pressure switch
PRS actuates and supplies power through manual reset
draft safeguard switch DSS. Both solenoid coils in gas
valve GV are energized, causing the valve to open and
permitting gas flow to the main burners, where it is ignited
by the pilot.
d. Simultaneously, solid-state time-delay circuit in the blower
control center is energized. Approximately 45 sec after the
R-W circuit is closed, heating fan relay coil HFR is
energized, closing the 115-v contacts of heating fan relay
HFR, and starting blower motor BLWM on heating speed.
EAC terminals energize with 115v when the blower is
operating on either heating or cooling speed.
e. When the thermostat is satisfied, the R-W circuit is broken,
de-energizing both solenoid coils of gas valve GV and the
solid-state time-delay circuit for the heating fan relay HFR.
The gas flow to the main burners immediately stops.
Approximately 120 sec (or 180 sec depending on the
blower off time selected) after main burners are extin-
guished, heating fan relay HFR is de-energized and blower
motor BLWM stops. The blower off delay can be perma-
nently changed to 180 sec by cutting the resistor. (See Fig.
9.)
f. If the pilot flame is extinguished, the thermocouple no
longer energizes the thermal magnet circuit of gas valve
GV. Gas flow to the pilot and main burners ceases until the
pilot is manually relit.
NOTE: When gas valve GV is energized, R-W circuit is closed.
After a power interruption, the gas valve closes within 7 sec and
HEATING
SPEED TAP
115-VAC TERMINAL
NEUTRAL
TERMINALS
COM PR-2 L2
EAC-2
CFR HFR
LO
HI
EAC-1
SPARE-1
COOLING
SPARE-2
SPEED TAP
TERMINAL
ELECTRONIC
AIR-CLEANER
TERMINALS
W Y1
CES0110074-01
24-VAC
THERMOSTAT
TERMINALS
→
Fig. 9—Control Center
the furnace skips the blower on delay and immediately starts the
blower.

2. Cooling mode

When the wall thermostat "calls for cooling" the R, G, and Y
circuits close. Simultaneously, the R-Y circuit starts the
outdoor condensing unit, the R-G circuit energizes cooling
relay coil CFR, and heating fan relay coil HFR. The normally
open contact of heating fan relay HFR and the normally open
contact of cooling relay CFR closes, energizing the cooling
speed of blower motor BLWM. The EAC terminals are
energized with 115v when the blower is operating on either
heating or cooling speed.

3. Continuous blower mode

When the R-G circuit is made, the blower motor operates on
cooling speed. During a "call for heat", the blower stops,
allowing the furnace heat exchangers to heat up more quickly.
When the blower motor comes back on it runs on heating
speed. The blower reverts to continuous operation after the
heating cycle blower off delay is completed.
START-UP PROCEDURES — Check to be sure that all connec-
tions have been properly made, then light the pilot using the
procedure outlined on the lighting/operation instructions label
attached to the furnace. However, when lighting the pilot for the
first time, perform the following additional steps:
1. Purge gas lines after all connections have been made and
check for leaks.
8
115-VAC
LINE
VOLTAGE
115-VAC
TRANSFORMER
1
PL-1
1 4 7
L1
2 5 8
PR-1
3 6 9
3
9-PIN
CONNECTOR
24-VAC COMMON
24-VAC POWER
R C G
BLOWER
24VAC
OFF-DELAY
COMMON
24-VAC FUSE
3-AMP ONLY
BLOWER
OFF-TIME
ADJUSTMENT
SEC-2
SEC-1
3-AMP
FU
FUSE
GROUND
SCREW
REQUIRED
A95463