WattMaster VAVBOX - Manual (Page 22)

Technical Guide
VAVBOX Controller 22
Other Checks
Space Temperature Sensor
If the Space Temperature Sensor is not reading a valid temperature, first
make sure that the Space Temperature Sensor is correctly wired and
that the terminal connections are all tight. If the problem persists, try
swapping the sensor with a known good Space Temperature Sensor. If
that sensor works when connected to the VAVBOX controller board,
you can assume you have a defective or damaged sensor.
Duct Air Temperature Sensor
If you suspect the Duct Air Temperature Sensor is not reading correctly,
make sure the wiring terminal connections are tight and that any wiring
splices are properly connected. You can check the operation of the Duct
Air Temperature Sensor by measuring the resistance or voltage using a
digital multimeter. Set the meter to DC Volts. Place the positive probe
on the AIN terminal and the negative probe on the GND terminal. Read
the DC Volts and find that voltage in Table 5 on the following page.
Read the temperature corresponding with that voltage and determine if
this is close to the actual temperature the sensor is exposed to. If the
temperature from the chart is different by more than a few degrees you
probably have a defective or damaged sensor. You can also check the
sensor resistance to determine correct operation. To read the resistance
set the meter to Ohms. Unplug the sensor connector from the board and
measure the resistance across the disconnected wires. This resistance
should match the corresponding temperature from Table 5 on the fol-
lowing page.
Airflow Sensor
If the Airflow Sensor seems to be reading incorrectly, first check the
Airflow Sensor’s modular cable connector and be sure it is firmly con-
nected to its mating connector on the VAVBOX controller board.
Check the Airflow Sensor tubing connections at the airflow pickup tubes.
The high pressure port of the sensor needs to be connected to the up-
stream pickup tube. The low pressure port of the sensor needs to be
connected to the downstream pickup tube.
If none of the above procedures solves the problem, remove power from
the VAVBOX controller. Shut down the HVAC unit supplying the duct
that the VAVBOX damper is located on. Be sure that no airflow is present
in the duct. Reapply power to the board and wait for the VAVBOX
controller to run through it’s calibration sequence. Restart the HVAC
unit and check the VAVBOX controller CFM readings. If the CFM read-
ing still seems to be in error, you probably have a defective Airflow
Sensor and will need to replace it.
Actuator
Check the Modular cable between the controller and the actuator. Be
sure both ends of the cable are firmly connected to the mating connec-
tors on the actuator and the VAVBOX controller board. Be sure the
damper moves freely and is not bound. Do this by pressing the actuator
clutch button and rotating the damper shaft in both directions to verify
smooth operation. If binding is present fix the problem as required.
Remove power from the VAVBOX controller. Reapply power and ob-
serve the damper rotation. If the actuator does not drive the damper in
both directions, the actuator is probably defective or damaged. Another
test that can be performed, is to swap cables with another known oper-
ating actuator to determine if the cable could be bad. If the problem
goes away you have a defective cable that must be replaced. You can
also try swapping a functioning actuator with the suspected defective
actuator. If this solves the problem then the defective actuator will need
to be replaced.
Expansion Board
If the Expansion Board does not seem to operate correctly, first make
sure the modular cable between the Expansion Board and the VAVBOX
controller is firmly connected at both ends. Be sure that the Expansion
Board has been configured correctly. The expansion board must be con-
figured using the Modular Service Tool, Modular System Manager or
Prism computer front end software, for your application, before it will
operate. You must configure it for the number of heat stages and if this
is a fan terminal, whether it is a Series or Parallel Flow fan terminal. On
a non fan terminal unit, when a call for heat is initiated the LED la-
beled RLY2 should light up. If the expansion board is configured as a
fan terminal, on a call for the fan, the LED labeled RLY1 should light
up. If the LEDs do not light up the Expansion Board is probably de-
fective and must be replaced.
Troubleshooting