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UNT Controller—Unitary (UNT) Controller
Table 26: Troubleshooting the UNT with HVAC PRO for Windows
Symptom Possible Cause Corrective Action
Indoor Fan Does Not
Run
Unit not in Occupied
mode.
Unit does not need
heating or cooling.
Fan off due to air flow
loss.
Use the Commissioning mode to
force the controller into Occupied
mode or insert a jumper across the
defined, occupied BI if the UNT is
already configured to Occupied
mode.
Check the configuration to verify if
the fan was to cycle during
Occupied mode.
Check air proving switch. Restart
by breaking and making unit power.
M100C/Zone Bus
Economizer Actuator
Does Not Open to
Minimum Position
Indoor fan not proven.
Actuator or linkage
Wiring problem
See above.
Remove actuator cover and check
for 24 VAC across T1 and T2.
Insert jumper CW to COM.
Actuator should fully open outdoor
dampers. Remove jumper.
Check that wire from Zone Bus on
UNT is connected to bus terminal
on actuator. Check address of the
M100C actuator; it should be 22.
Heating or Cooling Will
Not Turn On
Automatically
Zone Sensor not
connected.
Zone temperature not
above/below setpoint.
Heating or cooling
lockout from outdoor
temperature.
Delay timers present.
Ensure Zone Sensor is properly
connected with an 8-pin plug to the
UNT.
Simulate a load at the sensor using
HVAC PRO for Windows.
Simulate a value at the OA sensor
using HVAC PRO for Windows
Commissioning.
Wait until time delays have expired
(approximately five minutes).
ZT Display Contains
Dots
Configuration mismatch
between the controller
and the ZT (a ZTU100-0
is used with a UNTxxx-1
controller).
Upgrade the ZTU100-0 to a
ZTU100-1. Refer to the
Zone
Terminal Technical Bulletin
in this
manual for more information.
Binary Output Will Not
Turn On or Chatters
TRIAC Jumper is not set
correctly.
Load is not drawing
50 mA (minimum load
for triac).
Set jumper so that triacs are
switching proper side of
transformer.
Add a 1k ohm, 2-watt resistor
across the relay coil.
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