John Wood Commercial - 300-400K BTU - Manual (Page 8)

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blower is operating properly. The control system monitors
this switch and will disable heating operation if its contacts
are closed before the Combustion blower is energized or
open any time during a heating cycle. See Sequence Of
Operation on page 8.
11. Vent connection (exhaust elbow) - 4 inch PVC.
12. Combustion blower.
13. blocked Exhaust (vent) switch. Normally closed contacts
that open on a rise in pressure. This switch is used to
insure the Exhaust (vent) piping connected to the water
heater is not restricted. The control system monitors this
switch and will disable heating operation if its contacts
are open during a heating cycle.
14. VFD (variable frequency drive) blower motor drive. used
on AJWSH130400 models only.
15. Temperature-Pressure relief Valve. See Temperature-
Pressure relief Valve on page 15.
16. upper Temperature Probe, 1 of 2 temperature probes.
The water heater’s control system monitors this probe
to detect water temperature in the upper portion of the
storage tank.
The upper Temperature Probe also houses the ECO
(energy cut out) switch. This is a non adjustable high
temperature limit switch. The ECO switch contacts are
normally closed and will open on a temperature rise. See
High Temperature Limit Control (ECO) on page 40.
17. Water outlet connection 1 1/2” NPT.
18. uIM (user interface module). The uIM includes the
display circuit board, the control system’s LCD display
and operational buttons. used to adjust various user
settings and view operational information. See Control
System Operation on page 41.
top View
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FRONT
top View components
1. Water Heater’s 120 VAC on/off switch.
2. Powered anode rods. The water heater’s covered in this
manual are equipped with two powered (non sacrificial)
anode rods. Protective current is fed by the control system
to the titanium electrodes at the end of each anode rod. This
current flows through the water to the conductive surfaces
inside the storage tank which diminishes the corrosive effect
(rusting) of water when it comes in contact with steel.
3. Central Control board (CCb) enclosure. This enclosure
houses the control system’s main circuit board. The CCb
regulates water temperature and controls all water heater
functions, see Control System Operation on page 41.
4. 120 VAC junction box. Incoming power supply and ground
connections are made here. See Power Supply on page 13.
5. Intake air connection - 4 inch PVC.
6. blocked Intake Air switch. Normally closed contacts that
open on fall in pressure. This switch is used to insure intake
(combustion) air to the water heater is not restricted. The
control system monitors this switch and will disable heating
operation if its contacts are open during a heating cycle.
7. Water heater's 24 VAC gas Valve.
8. Supply gas line connection. See the requirements for the
Supply gas Line on page 13.
9. Low gas Pressure switch. Normally open contacts that close
on a rise in pressure. This switch is used to insure supply
gas pressure is above minimum requirements. The control
system monitors this switch and will disable heating operation
if its contacts are open during a heating cycle. See Table 3
and the gas Pressure requirements on page 13.
10. blower Prover switch. Normally open contacts that close on a
rise in pressure. This switch is used to insure the Combustion
figure 3