Tweco 15XC Merlin - Manual (Page 103)

Manual 0-2251 5-31 CUSTOMER/OPERATOR SERVICE
5.12 SERVICE AND TEST PROCEDURES (continued)
F. Pressure Sensing Circuit
(continued)
G. Gas Solenoid Circuits
H. Coolant Flow Sensor
Circuit Check
I. Coolant Conductivity
Circuit
2. If the voltage at J1-7 is less than 1V, check the voltage at
J3-3. If the voltage at J3-3 is greater than 12 vdc, replace
the logic board. If the voltage at J3-3 is less than 12 vdc,
replace the LED board.
1. Set the RUN/SET/PURGE switch to SET position.
Measure continuity between the center terminal of the
switch (wire #62) and each outer terminal (wires #61
and 63). If the resistance is less than 1000 ohms, replace
the RUN/SET/PURGE switch.
2. If the resistance is greater than 1000 ohms, check for 120
VAC between wire #110 and J2-8 for plasma and J2-10
for secondary. If 120 VAC is present at one point and
not the other, replace the logic board.
3. If no voltage is present at J2-8 or at J2-10, check for 120
VAC at J2-1 (the logic board input). If 120 VAC is
present at J2-1, replace the logic board. If not, check the
120 VAC voltage supply (see Section 5.12-Test A).
The flow sensor (FS1) for the coolant is calibrated for 0.75
gpm. When adequate coolant flow satisfies FS1 it closes,
connecting J1-5 on the logic board to J1-4 (common).
Measure voltage between J1-5 and J1-4 or TP1. If J1-5 is
greater than 1 volt FS1 or connections to FS1 are faulty. If
J1-5 measures close to 0 vdc, check J3-2. If J3-2 measures
less than +12 vdc, and the coolant flow indicator is not lit,
replace the LED PC board. If J3-2 measures greater than
+12 vdc, replace the logic board.
The conductivity probe consists of two insulated pins that
extend into the coolant reservoir. The logic PC board
sends out an AC voltage level on J2-24 that varies with the
conductivity of the coolant.
1. Disconnect one of the wires to the conductivity probe
(wire #57 or 58). The logic PC board will see infinite
resistance and the coolant conductivity LED indicator
should be lit. If the coolant conductivity indicator is lit,
replace the coolant. If the problem remains, replace the
conductivity probe.
2. If the coolant conductivity indicator is not lit with the
probe disconnected, measure between the logic board
common (TP1) and J3-1. If the voltage measures below
+12 vdc, replace the LED PC board. If the voltage
measures above +12 vdc, replace the logic board.