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SPECIFICATIONS Magic-Pak: HW/HWC
2-28
SRM-HW/HWC 2/99
Detailed Sequence - HWC122, 182, 242, 302
(w/Fenwal 05-29 Ignition Control)
Refer to Figure 2-5
POWER
Line Voltage
When the service disconnect switch is closed, power is
sent to the unit (unit in standby, no signal from the
thermostat). Power (208 - 230 volts A/C) is supplied
to both black wires located in the junction block on top
of the unit.
Line voltage will be present at the following locations:
First black wire
1. L-1 on the ignition module
2. L-1 on the contactor
3. L-1 on the blower control board
4. Terminal on the transformer marked 208V or
240V (whichever is being used)
Second black wire
1. Supplies power to the induced draft blower
2. L-2 on the contactor
3. Common terminal on the transformer
4. T-2 on the contactor
5. Red wire on the R terminal of the compressor
6. Red wire to the common terminals on the capaci-
tors
Low Voltage (24 VAC)
With the unit at rest (no call from the thermostat), 24
volts A/C will be found at these points:
1. Red wire exiting the top of the unit
2. Terminal marked 24VAC on the ignition control
3. Terminal R on the blower control board
CALL FOR HEAT
Line Voltage
The thermostat closes the circuit between R and W.
The following is the sequence of operation for the line
voltage side of the unit:
1. Terminal TS (24-volt) energizes on the ignition
control, causing a relay in the ignition control to
close. This sends line voltage to the terminal
marked IND, causing the induced draft blower to
start.
2. When W is energized, a 24-volt signal is also sent to
the W terminal on the blower control board. The
24-volt signal starts the timer on the blower con-
trol board. After 60 seconds, the heat speed relay
on the blower control board closes. This sends
line voltage from the terminal marked HEAT to the
circulating air blower, starting the blower. The
induced draft blower and the circulating air
blower continue to operate until the heat call is
satisfied, interrupting the circuit between R and W.
The W terminal de-energizes, causing the blower
relay to open approximately 90 seconds later. This
interrupts the line voltage to the circulating air
blower and the blower shuts down.
Low Voltage
1. A call for heat closes the circuit in the thermostat
between R and W, sending a 24-volt signal to the
white wire on the unit.
2. The white wire goes to the C terminal on the limit
switch, ignition control terminal TS and terminal
W on the blower control board.
3. When W energizes, the timer starts a countdown to
circulating air blower “on”. The blower starts in
approximately 60 seconds.
4. The 24-volt signal sent to the TS terminal closes a
relay in the ignition control. This starts the
induced draft blower by energizing terminal IND
on the ignition control.
5. As the induced draft blower comes up to speed
and creates enough negative pressure, the pres-
sure switch closes. The 24-volt signal is sent from
the pressure switch to one side of the Normally
Closed manual reset rollout switch. If the
rollout switch is closed, the 24-volt signal is
passed through the switch to the P.SW terminal on
the ignition control. This initiates a 30-second pre-
purge period.
6. After the 30-second pre-purge period, a trial for
ignition starts by energizing the spark terminal and
the V1 terminal simultaneously. The 24-volt signal
from V1 energizes the gas valve solenoid, causing
it to open. These actions cause the burners to light.
7. After the burners are lit, a flame sense is picked up
by the flame sense rod located at the opposite
end of the burner rack from the spark electrodes.
The flame sense signal is sent to the S1 terminal of
the ignition control. The unit continues to operate
as long as W is energized.
8. When the call for heat is satisfied, the circuit be-
tween R and W is interrupted, de-energizing W.