iWorx® MPU2
30
505-009, Effective: April 28, 2014
© 2014 Taco Electronic Solutions, Inc.
Fan Proof
When there is a call for heating or cooling, the fan output is energized. A fan status input is provided for monitoring the
operation of the fan. When the fan is initially turned on, there is a 30 second delay before the fan status is checked. If at
any time after the delay, the fan status indicates the fan is not running, a fan failure condition is generated. The heating
and cooling stages are interlocked with the fan. When a fan failure condition exists, the heating stages, cooling stages
and the fan immediately turn off. The controller must be reset to clear this condition.
NOTE:
If not providing a fan proof switch, the dip switch for the fan proof input must be configured with the (0-10V)
switch set to “on” and the “Vth” set to off. After a fan failure, the controller's status LED changes from green to solid red.
To return the controller to normal operation after the failure condition is resolved, you must reset the controller by
removing and reapplying power or by using the controller reset feature on the LCI.
MPU2 and VAVD Communications
The MPU2 and its associated VAVD controllers transfer information, depending on the number of VAVD controllers
configured. The MPU2 polls a VAVD controller every 5 seconds to transfer information necessary for control. The fol-
lowing information is transferred from the MPU2 to the VAVD controller:
• Operational Mode: primary cool, primary heat, and primary off
• Occupancy Mode: occupied, unoccupied, and bypass
• Alarm Conditions: IAQ Mode and Heat Failed On
The following information is transferred from the VAVD to the MPU2 controller:
• Zone temperature
• Calculated Heating Setpoint
• Calculated Cooling Setpoint
• IAQ Sensor Status (safe, alarm)
• Local Alarm (VAVD shutdown)
• Occupancy Mode: occupied, unoccupied, and occupied extension)
• Supplemental heat status: on, off
Associating VAVDs
In order for the MPU2 and VAVDs to share information, the controllers need to be associated. To associate the VAVDs
to the MPU2, you first need to select the MPU2 from the LCI's list of controllers. Once the MPU2 has been selected,
depress the
HVAC Setup
button followed by the
Zone Members
button. You will see a list of all VAVDs on the net-
work, with the designation “Included” or “Excluded” showing on each line. To include a VAVD, simply depress the
desired VAVD in the list and it will show “Included” and the color will change to Red. After all the desired associations
are complete, depress the
Save
button so the information will be sent to all associated controllers.
Supply Air Temperature Monitoring
The MPU2 monitors the supply air temperature to determine if the heating and cooling stages are operating properly.
During heating mode, if the supply air temperature does not rise above the heat mode alarm setpoint after a 10-minute
delay, a heat mode alarm is generated. During cooling mode, if the supply air temperature does not drop below the cool
mode alarm setpoint after a 10-minute delay, a cool mode alarm is generated.
The MPU2 has provisions for detecting a gas valve that has been become stuck in the open position. The stuck gas
valve sequence helps to prevent overheating the HVAC unit.
