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14-Crankcase Heater Delay DL48 & Crankcase
Heater Relay K191
Delay DL48 and relay K191 keep crankcase heater de-en
ergized during and immediately following compressor shut
down. They ensure the crankcase heater is off while com
pressor is energized.
15-Gas Relay K72 (two stage units)
Relay K72 is normally closed and controls combustion air
inducer B6. K72 switches the inducer B6 to high speed in
response to two stage heat demand.
16-Burner Control A3
WARNING
Shock hazard. Spark related compo
nents contain high voltage which can
cause personal injury or death. Discon
nect power before servicing. Control is
not field repairable. Unsafe operation
will result. If control is inoperable, sim
ply replace the entire control.
The main control box (see figure 2) houses the burner con
trol A3.
The ignition control provides four main functions: gas valve
control, blower control, ignition, and flame sensing. The
control has a green LED to show control status (table 1).
The unit will usually ignite on the first trial and A3 allows
three trials for ignition before locking out. The lockout time
is 1 hour. After lockout, the ignition control automatically re
sets and provides three more attempts at ignition. Manual
reset after lockout requires removing power from the con
trol for more than 1 second or removing the thermostat call
for heat for more than 1 second but no more than 20 sec
onds. 24 volt thermostat connections (P2) and heating
component connections (J1) are made through separate
jackplugs. See table 2 for thermostat terminations and ta
ble 3 for heating component terminations.
Flame rectification sensing is used on all units. Loss of
flame during a heating cycle is indicated by an absence of
flame signal (0 microamps). If this happens, the control will
immediately restart the ignition sequence and then lock out
if ignition is not gained after the third trial. See System Ser
vice Checks section for flame current measurement.
The control shuts off gas flow immediately in the event of a
power failure. Upon restoration of gas and power, the con
trol will restart the ignition sequence and continue until
flame is established or system locks out.
TABLE 1
LED
STATUS
Slow Flash Normal operation. No call for heat.
Fast Flash Normal operation. Call for heat.
Steady Off
Internal Control Fault, No Power To Board
or Gas Valve Relay Fault
Steady On Control Internal Failure.
2 Flashes Lockout. Failed to detect or sustain flame.
3 Flashes
Rollout switch open / Prove switch open or
closed.
4 Flashes Primary High Limit switch open.
5 Flashes Flame sensed but gas valve not open.
TABLE 2
P2 TERMINAL DESIGNATIONS
Pin # Function
1 R 24 Volts to thermostat
2 W1 Heat Demand
3 Y Cool Demand
4 C Common
5 G Indoor Blower
6 BL OUT Indoor Blower Relay
7 W2 Second Stage Heat
TABLE 3
J1 TERMINAL DESIGNATIONS
Pin # Function
1 Limit Switch Out
2 Rollout Switch / Prove Switch Out
3 Gas Valve Common
4 Gas Valve Out
5 Rollout Switch / Prove Switch In
6 Limit Switch In
Operation
On a heating demand, the ignition control checks for a
closed limit switch and open combustion air prove switch.
Once this check is complete and conditions are correct, the
ignition control then allows 30 seconds for the combustion
air inducer to vent exhaust gases from the burners. When
the combustion air inducer is purging the exhaust gases,
the combustion air prove switch closes proving that the
combustion air inducer is operating before allowing the ig
nition control to energize. When the combustion air prove
switch is closed and the delay is over, the ignition control
activates the gas valve, the spark electrode and the flame
sensing electrode. Once the gas valve is energized the
non-adjustable 40 second indoor blower delay period be
gins. Sparking stops immediately after flame is sensed or at
the end of the 8 second trial for ignition.
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