Pentair Pool Products MiniMax NT Series Service Manual page 45

STEP-BY-STEP ELECTRICAL TROUBLESHOOTING
MINIMAX NT SERIES HEATER w/6800 BOARD
• Power to the heater should be configured properly at the terminal block, (for 120v the neutral lead
always goes to the center lug of terminal block).
• From the terminal block the power flows through the internal shut off switch at the bottom of the
J-Box. (This voltage will be the same as the supply voltage for the heater.)
• The power now is divided between the 120v and 240v female connectors; (from the factory the
heater is configured for 240v to avoid damage to the transformer).
• The male connector should be plugged into the proper 120v or 240v female connector before turning
on the heater. This provides the proper voltage to the transformer, fan and ignition module.
• High voltage supplied to the transformer is changed to 24vac to control the ignition process, (output
voltage is relative to the input voltage and it should range from 24-29vac). Voltage readings below
24vac indicate a problem. (NOTE: The heater is also certified at 85% of 120v/240v too, therefore,
the voltage could be as low as 22.5. However, we do NOT recommend operating the heater at that
condition for a long period at all.)
• The 24vac from the transformer is supplied to the 24vac terminal on the circuit board as well as the
24vac lead on the module. This is the main power supply for the circuit board as well as the module.
• To start the ignition process, there must be a call for heat. This is provided by the thermostat circuit
on the circuit board. If the thermostats are turned up and the pool/spa switch is in either the Pool or
Spa position, if there is no call for heat, then check the temperature probe connection on the back of
the circuit board. If the connection is good, test with a known good sensor.
• Once the thermostat circuit is completed, power is supplied to the safety circuit. The power flows as
follows:
1. From the circuit board to the pressure switch and back to the board (this will illuminate the
pressure light (PRESS) on the front of the board).
2. From the circuit board to the high limits and back to the board, (this will illuminate the high
limit light (HTEMP) on the back of the board).
3. From the circuit board to the thermal fuse and back to the board, (this will illuminate the T-fuse
light (TFUSE) on the back of the board).
• When the thermostat circuit and safety circuits have been completed, 24vac is supplied to the
fan-proving switch, (where it will wait for the fan to come on), and to the IND terminal on the top
left of the ignition module.
• When the IND terminal is energized, the contactor between F1 and F2, (inside the Fenwal Module),
closes sending power to the fan. If the fan does not come on, disconnect the wires between F1 and
F2 and check for continuity through F1 and F2 with the IND terminal energized.
Rev. B 2-11-04
OF THE
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P/N NTSM03