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1)
POWER SUPPLY
Plug the heater into a 120 Volt grounded receptacle. Power is now at the 20 amp fuse and the
3
amp circuit breaker. Power light illuminates.
2)
20 AMP FUSE & 3 AMP BREAKER
If the circuit breaker and fuse are good there will be power at the thermostat and at the motor
relay (normally open). Fuse light illuminates.
3)
ON SWITCH
With the "ON" switch on, it sends power to the "OFF" switch and the control relay. (Normally
open terminal and it's solenoid coil.)
4)
CONTROL RELAY
After receiving power from the "OFF" switch, the relay closes, a loop between the 3amp breaker
and the (NC) "OFF" Switch.
5)
OFF SWITCH
Power is sent from "OFF" Switch to (L1) terminal of DSI control and the (COM) terminal of
the thermostat.
6)
THERMOSTAT
When the thermostat calls for heat there will be power at (TH) terminal of the DSI control and
Air Flow Switch (COM) Terminal.
7)
DSI CONTROL
Sends power from (IND) terminal to coil of the motor relay.
8)
MOTOR RELAY
With its coil energized it closes its contacts, sending power to the fan motor.
9)
FAN MOTOR
Turns the fan blade causing the air flow switch to close.
10) AIR FLOW SWITCH'S
Received their power from the thermostat and sends the power to the indicator light and the
DSI control (PSW) terminal.
11) DSI CONTROL
Sends power from the (V1) post to the high limit.
12) HI TEMPERATURE LIMIT SWITCH
This switch has normally closed contacts, it sends power to the gas solenoid valves. Lo valve
and Hi valve lights illuminate.
13) GAS SOLENOID VALVE
With the coil energized, the valve opens, gas passes through to the burner and ignites.
14) FLAME SAFEGUARD CONTROL
This is now sensing flame through the flamerod and the spark stops. The heater is operating.
15) THERMOSTAT
When it is satisfied, the contacts open taking power away from the (TH) terminal of the DSI
control, the gas valve closes, and the built-in fan delay timer is activated.
16) BUILT-IN FAN DELAY TIMER ON DSI CONTROL
This will operate the fan motor for approximately 10 seconds and turns the fan off.
MODEL 750NEF
SEQUENCE OF COMPONENT OPERATION
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