Schematic Diagram - A.O. Smith T-H3J-DV Service Manual

5. Schematic diagram

The diagram below refers to both the Direct Vent Indoor models and Outdoor models.
Direct Vent Indoor models only
Hi-limit switch for exhaust
Intake port
Exhaust thermistor
Drain pan
Hi-limit switch
540 (T-H3) models only
Heat exchanger thermistor
Bypass valve
Fan motor for combustion
Flow adjustment valve
with Flow sensor
ON-OFF-switch for power supply
Outlet thermistor
Inlet thermistor
1. When a hot water tap is opened, cold water enters the water heater.
2. The water flow sensor detects this water flow and sends this information to computer.
3. The computer initiates fan motor and sends signal to igniter to create ignition spark.
4. The main, proportional, and solenoid gas valves open to allow gas input.
5. The gas ignites and flames appear inside the burner chamber.
6. Water circulates through the heat exchanger and is heated up to the set temperature.
7. Using thermistors to measure temperatures, the computer modulates the gas and water valves to
ensure proper output water temperatures.
8. When the tap is closed, the water heater shuts down.
The Direct Vent Indoor models detects the exhaust temperature by using
NOTICE
exhaust thermistor and hi-limit switch for exhaust during procedures of 3 to 8.
240 (T-H3J), 340 (T-H3S) and 540 (T-H3) models Service Manial
PCB
Heater
Drain plug
Inlet drain
plug filter
13
Exhaust
Secondary heat exchanger
Primary heat exchanger
O.H.C.F
Air-fuel ratio rod
Flame rod
Igniter rod
Igniter
Gas solenoid valve 1
Main gas valve
120
Condensate drain
VAC
Gas proportional valve
Gas solenoid valve 2
Gas solenoid valve 3
Surge box
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CONFIDENTIAL
Ver. 1.00