
VCES-DDC-IOM-1C
23
Table D3: DDC Troubleshooting Guide
Problem Cause Solution
Exhaust fan will not turn on.
Unit is in recirculation defrost
(units equipped with recircu-
lation defrost).
BacStat will flash ‘dF’ in upper left corner. Wait for defrost mode
to finish its timed sequence.
Unit is in unoccupied recircu-
lation
(units with recirculation
damper).
BacStat will show ‘UR’. Check if you have a contact closure
across 305 and 306.
Damper end switches are not
making.
Check your field wires connected to PNL 310 and 311 for a
closed connection.
Damper will not open. Electrical supply interrupted.
Check wiring on damper actuator.
For the outside air damper actuator and recirculation damper
actuator (if equipped), measure a 24 VAC across PNL terminals
330 and 302.
For the exhaust air damper actuator, measure a 24 VAC across
factory wired terminals 332 and 302.
Supply fan will not turn on.
Unit is in exhaust defrost
(units equipped with exhaust
defrost).
BacStat will flash ‘dF’ in upper left corner. Wait for defrost mode
to finish its timed sequence.
Damper end switches are not
making.
Check field wires connected to PNL 309 and 310 for a closed
connection.
Additional Troubleshooting:
__ Verify DDC jumpers are correct.
__ Verify expander board jumpers and address (dip switch settings) are correct.
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