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Rev. C 11-1-01 P/N 471593
21
SAFETY CONTROLS
AIR PRESSURE (FAN) SWITCH
The air pressure switch is a safety device used to insure
that the blower (fan) is operating and has been
designed to monitor the vacuum (negative) pressure
within the blower housing. The air pressures switch
is factory set and is in the ignition module circuit—
the ignition module does not operate unless the air
pressure switch and all safety switches are closed.
NOTE
Some models of MiniMax NT Low NOx heaters,
manufactured before 10-15-01, used both a HIGH
and LOW air pressure switch.
WATER PRESSURE SWITCH
The water pressure safety switch closes when there is
a sufficient flow of water to the heat exchanger to
safely operate the heater. The switch operation must
be verified during initial operation of the heater after
installation—the switch is set at 1 PSIG and the switch
contacts must not be closed in the absence of water
flow. NOTE: See, Below Pool Level Installation
instructions on page 13. The switch may remain closed
with no water flow if there is more than a 3 ft. elevation
difference between the heater (heat exchanger) and
the pool water line—if this is the case, the water
pressure switch must be reset to maintain open switch
contacts with no water flow.
NOTE
If the pool is more than one floor above or one floor
below the heater, the pressure switch may have to
be replaced with a flow switch.
LOW GAS PRESSURE SWITCH
(LOW NOx Versions Only)
The MiniMax NT Low NOx heater uses a low gas
supply pressure switch, ahead of the gas valve, to
prevent operation of the heater when the gas supply
pressure is below the minimum required for proper
operation of the burners. The switch is factory set. In
the event that the switch does not close and prevents
the firing of the heater, the cause of the low gas supply
pressure must be corrected. Typical causes are
undersized supply piping, undersized gas meter or low
gas regulator setting (gas supply regulator and gas
meter problems are typically corrected by your local
gas company).
Basic Operation
AIR PRESSURE SWITCH
Adjustment Knob
Typical Water Pressure Switch
Low Gas Pressure Switch
Figure 18.
Figure 19.
Figure 20.