Pentair Pool Products MiniMax NT Series Service Manual page 41

Troubleshooting
1. The Fan Vacuum Switch is a normally open switch
that closes on a decrease of pressure in the fan exhaust
housing. It then sends 24 VAC through the white wire
to the Ignition Module at the TH terminal to start the
ignition sequence. Applying a vacuum to the barbed
fitting where the orange tube is attached can test the
switch and its circuit. To perform this test, SHUT
OFF POWER, connect the leads of a multimeter set
to Ohms to each terminal on the switch, remove orange
tube from switch and, using a short piece of ¼ in. ID
tube attached to the barbed fitting, draw air from the
switch to see if it closes.
2. Checking to see if there is 24 VAC on the white wire
terminal can also check the Fan Vacuum Switch during
operation.
3. If the Fan Vacuum Switch is good but it does not close
when the fan is operating and, therefore, power is not
sent to the Ignition Module, the problem is in the orange
tube or the connector in the Fan Housing is clogged.
4. If the Fan Vacuum Switch closes but 24 VAC is not sent
to the Ignition Module, the problem is in the white wire.
Troubleshooting
1. The Hot Surface Igniter can be checked four different ways:
a. Voltage Check: Check for 120 VAC across two wires
after 15 second pre purge time has expired.
b. Amp Draw: Check the HSI circuit for 0.5 +/- .05 amps
after 15 second pre purge time has expired, (see picture).
c. Continuity: Turn OFF electric supply to heater,
disconnect HSI leads and, using an Ohm setting, look
for any reading greater than zero or OL.
d. Visual: Remove burner Flash Back Shield to allow
visual inspection. The HSI should glow for about 47
seconds after the 15-second pre-purge cycle. It also
should be located above and parallel to the burner.
2. Before replacing the HSI, be sure that the heater frame and electric circuit are properly grounded,
as this will affect the performance of both the HSI and the Flame Sensor.
Rev. B 2-11-04
TESTING THE FAN VACUUM SWITCH
Attach ¼" ID
Test Tube here
Orange Vacuum Tube
connector in Fan Housing
TESTING THE
HOT SURFACE IGNITOR (HSI)
41
Check Continuity
from White to
Orange Wire with
Power turned OFF
P/N NTSM03