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P/N 472089 Rev. E 4-19-05
22
SAFETY CONTROLS
VACUUM AIR PRESSURE (FAN) SWITCH
The air pressure switch, (see Figure 20), is a safety device
used to insure that the combustion air 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 connected upstream
of the ignition module. The ignition module does not
operate unless the air pressure switch and all safety switches
are closed.
WATER PRESSURE SWITCH
The water pressure switch, (see Figure 21), closes when
there is a sufficient flow of water to the heat exchanger to
safely operate the heater. The switch has been preset by
the Factory at 1½ PSI for operation. NOTE: See, Below
Pool Level Installation instructions on page 8. 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 by a qualified service
technician 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 water pressure switch may
have to be replaced with a flow switch.
THERMAL FUSE
This is a single-use switch, mounted on combustion
chamber jacket divider (inner front panel). The fuse, (see
Figure 22), is activated by excessive temperature due to
abnormal operating conditions. Upon detection of
excessive heat within the inner front panel, the fuse will
open the safety circuit causing shutdown of the heater.
LOW GAS PRESSURE SWITCH
The MiniMax NT LN model heater uses a low gas supply
pressure switch, (see Figure 23), 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).
Typical Water Pressure Switch
AIR PRESSURE SWITCH
Figure 20.
Air Pressure Switch
Thermal Fuse
Section IV. Operation
Figure 22.
Adjustment Knob
Figure 21.
Low Gas Pressure Switch
Figure 23.