LAARS U.H.E. - Service Manual - Manual (Page 12)

LAARS Heating Systems Page 12
Refer to ignition module
illustration, Is there 24VAC
between P3(7) and P3(8)?
Y
OK, thermostat is
calling for heat.
Turn off power to heater.
Disconnect YELLOW and RED wires from the
thermostat board at location N.O. and COM shown in
photo at right. Use a jumper to connect these two
wires together as shown in photo at right.
Restore power to heater.
Did heater cycle on?
N
Check thermostat sensor
for proper resistance
(OHMS) across blue wires.
(See page 13)
Are readings correct?
(see photo at right)
Check temperature dial for
proper resistance (OHMS)
(See Appendix B,
temperature dial resistance)
Are readings correct?
(see photo at right)
Y
Y
Replace
thermostat sensor.
(see page 12)
Replace temperature dial
(potentiometer).
(see page 16)
N
N
N
Replace thermostat
circuit board.
(see page 15)
Y
Check sensor harness
continuity.
Is there continuity?
Check temperature dial
harness continuity.
Is there continuity?
Replace harness.
Y
N
Replace harness.
N
Y
See page 14
IGNITION MODULE
IMPORTANT NOTE: This procedure assumes a cool tank
Rotate temperature
dial to highest setting.
Thermostat
not calling
WARNING
120 volt potential exposure. Use
caution making voltage checks
to avoid personal injury.
12
Thermostat
Sensor
Temperature Dial
Yellow & Red
wires shown
jumpered
Yellow Wire
(COM)
Red Wire
(N.O.)