Specifications

Page 18
FIGURE 17
THERMOSTAT DEMAND
COMBUSTION AIR BLOWER
GAS VALVE
IGNITION SPARK
BLOWER
IGNITION TRIAL
SECONDS 0 30
ON
OFF
FENWAL - IGNITION CONTROL TIMING
30
30
HEATING
CYCLE
6.8 (+3.4, -2.0) SEC.
END OF
THERMOSTAT
DEMAND
123
Blower starts 30 to 45 seconds after flame is sensed. When ignition occurs on any trial, heating cycle begins. Ignition spark remains on for a total of 6.8
+3.4, -2.0 seconds from the beginning of the trial period. If flame sensor detects loss of flame during heating cycle, gas valve remains open and ignition
spark begins for one second. If flame is detected before the end of one second, spark stops and the heating cycle continues. If flame is not detected during
the one second ignition retrial, the control cycles through the complete ignition sequence before locking out.
110+20 sec.
B-Heat Exchanger (Figure 12)
The GCS24 uses aluminized steel inshot burners with match
ing tubular aluminized steel heat exchangers and a twostage
redundant gas valve. The GCS24 uses an eight tube/burner
assembly. Each burner uses a burner venturi to mix gas and
air for proper combustion. Combustion takes place at each
tube entrance. As hot combustion gases are drawn upward
through each tube by the combustion air blower, exhaust
gases are drawn out the top and fresh air/gas mixture is
drawn in at the bottom. Heat is transferred to the air stream
from all surfaces of the heat exchange tubes. The supply air
blower, controlled by the ignition control or the control system
(depending on which control system is installed), forces air
across all surfaces of the tubes to extract the heat of combus
tion. The shape of the tubes and a deflector ensure maximum
heat exchange.
The gas valve accomplishes staging by allowing more or less
gas to the burners as called for by heating demand. Heat ex
changers accomplish staging by cycling the second stage op
erator of the gas valve. When thermostat demand calls for
more heat, the second operator of the gas valve opens to al
low more gas to the burners.
C-Burner Assembly (Figure 18)
The burners are controlled by the spark electrode, flame
sensing electrode, gas valve GV1 and combustion air blower.
The spark electrode, flame sensing electrode and gas valve
are directly controlled by the ignition control. The ignition con
trol is controlled by the combustion air blower. The combus
tion air blower is controlled by heating demand from the ther
mostat or control system.
1-Burners
All units use inshot burners (see figures 18 and 19).
Burners are factory set and do not require adjustment.
Burner air shutters are designed to be fully open only. A
peep hole with cover is furnished in the heating access
panel for flame viewing. Always operate the unit with the
access panel in place. Burners can be removed individu
ally for service. Burner maintenance and service is de
tailed in the SERVICE CHECKS sections of this manual.
FIGURE 18
TYPICAL GAS MANIFOLD ASSEMBLY
GAS VALVE GV1
BURNERS
AIR SLOTS
BURNER
RETAINER
SCREW
MANIFOLD
ORIFICE
GAS VALVE POSITION
SLIGHTLY DIFFERENT
IN DUAL HEAT EX
CHANGER MODELS
2-Orifice
Each burner uses an orifice which is precisely matched to
the burner input. The orifice is threaded into the burner
manifold. The burner is supported by the orifice and will
easily slide off for service.
Each orifice and burner are sized specifically to the unit.
Refer to Lennox Repair Parts Listing for correct sizing in
formation.