IM 1272 • OPTILINE VERTICAL FAN COILS 10 www.DaikinApplied.com
Troubleshooting
Troubleshooting
• 2-Pipe valve control heating/cooling units
• 2-Pipe valve control heating/cooling auxiliary heat units
• 2-Pipe valve control heating/cooling with total electric
heat units
• 4-Pipe valve control heating/cooling units
Most problems can be promptly diagnosed at the thermostat.
The fan assembly is accessible and removable through the
return air opening, after removal of the return air grill and fan
access cover. The fan assembly has a five wire plug harness
for power and 0-10VDC speed control signal.
The 2-pipe units are equipped with a change-over aqua-
stat mounted on the riser accessed through the return air
panel. The 2-pipe with auxiliary heat units have 2 aqua-stats
and the 2-pipe with primary electric heat have no aqua-stat.
Thermostats and control valves are 24VAC.
If Fan Motor Fails To Start
• Check main power supply, (circuit breaker) and unit
switch are “ON” and unit has power
• Set thermostat ON/OFF switch to “ON” and press fan
button to “ON”
• If fan will not operate, check that there is 24VAC coming
from the transformer
• If 24VAC is not present, replace the transformer
• If 24 VAC is present from the transformer, check the
thermostat wiring connections and motor wiring harness
plug and thermostat connections
• If all is good and system is 4-pipe (no aquastat), check
the DC voltage on terminals 11 & 12 on the thermostat. If
no voltage is present, replace the thermostat
• If the voltage is between 1 & 10VDC on terminals 11 &
12, and there is supply voltage to the fan motor, replace
the fan assembly
• If the system is change-over or has auxiliary electric
there, check the voltage at the aquastats*
• If no voltage is present at BLK or YEL, replace the
aquastat
* Aquastat with black, yellow and orange wire leads
closes for heating at 85F +/- 5F through BLK and ORG
and cooling at 65F +/ 5F through BLK and YEL.
Control Valve Fails to Operate
Check the voltage from the thermostat, if no voltage, replace
the thermostat. If 24 volts or a DC voltage for modulating
valves is present, replace the actuator. If the system has an
aquastat(s), check that 24 volts is present from the aquastat.
If 24 volts is present, replace the actuator. If no voltage is
present, replace the aquastat
Electric Heat Coil Fails to Operate
The electric heat coil module is located behind the motor
cover above the fan and consists of a relay operated by the
thermostat, a high temperature automatic limit control and
thermal cut-off directly attached to the heating element. Both
the thermal cut off and high temperature limit control are in the
heating coil power circuit.
The temperature limit control sensing element protrudes
through the control box directly above the heating element
to sense over heating of the coil including fan failure. This is
an auto-reset type and will reset when the temperature drops
below the preset limit.
The thermal cut off is located below one of the coil terminals
directly attached to the coil element. Both safety devices can
be replaced easily in the field if continuity test reveal an open
circuit. If these circuits are both closed, replace the heating
element by removing the 4 screws securing the mounting plate
and removing the entire heating assembly.
