Watlow PM LEGACY™ Limit Controller • 104 • Appendix
Indication Description Possible Cause(s) Corrective Action
No Display No display indication
or LED illumination
Either red or green
display is blank.
Check factory page,
custom menu 1 and
2 for correct settings.
Default is Custom 1 =
Process and Custom-
er 2 = Limit Status
• Power to controller is off
• Fuse open
• Breaker tripped
• Safety interlock switch
open
• Separate system limit con-
trol activated
• Wiring error
• Incorrect voltage to con-
troller
• Turn on power
• Replace fuse
• Reset breaker
• Close interlock switch
• Reset limit
• Correct wiring issue
• Apply correct voltage,
check part number
No Serial
Communication
Cannot establish se-
rial communications
with the controller
• Address parameter incor-
rect
• Incorrect protocol selected
• Baud rate incorrect
• Parity incorrect
• Wiring error
• EIA-485 converter issue
• Incorrect computer or PLC
communications port
• Incorrect software setup
• Wires routed with power
cables
• Termination resistor may
be required
• Set unique addresses on
network
• Match protocol between
devices
• Match baud rate between
devices
• Match parity between de-
vices
• Correct wiring issue
• Check settings or replace
converter
• Set correct communication
port
• Correct software setup to
match controller
• Route communications
wires away from power
wires
• Place 120 Ω resistor across
EIA-485 on last controller
Temperature
runway
Process value contin-
ues to increase or de-
crease past set point.
• Controller output incorrect-
ly programmed
• Thermocouple reverse
wired
• Controller output wired in-
correctly
• Short in heater
• Power controller connec-
tion to controller defective
• Controller output defective
• Verify output function is
correct (heat or cool)
• Correct sensor wiring (red
wire negative)
• Verify and correct wiring
• Replace heater
• Replace or repair power
controller
• Replace or repair controller
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