General troubleshooting
Table 9: Troubleshooting
Problem
Possible cause and correction
Verification
Controller is OFF.
•
Transformer has tripped:
•
Power is at Primary of
Transformer, 0V at Secondary.
•
Breaker/Fuse has tripped:
•
Power is at Primary of
Transformer, 24V at Secondary,
0V at Fuse/Breaker.
Cause:
1. Transformer is shorted.
2. 24 VAC powered sensor is not
wired with the same polarity as the
controller.
3. SA Bus device is not wired with the
same polarity as the controller.
Correction:
1. Ensure polarity of ~24 V COM / ICOM /
+ 15VCOM/SA BUS COM on the
controller, auxiliary devices, and I/O is
the same.
2. Ensure OUT1-OUT3 terminals of binary
outputs are not connected to ~24
VAC COM, and verify that OCOM1-
OCOM3 are not connected to ~24 VAC
HOT (these terminals are internally
sourced).
3. Verify the short circuit has been
resolved with an ohm-meter.
4. Reset the breaker/fuse or replace the
transformer.
Note:
When replacing the
transformer, it is recommended to
replace with a model that utilizes a
resettable circuit breaker. A circuit
breaker makes solving wiring
problems easier.
1. Disconnect the Secondary of the 24
VAC transformer.
2. Use an ohm-meter to measure
between ~24 V HOT and COM; there
must be no short circuit.
Note:
Some installations require
the Secondary of the Transformer
to be Earth Grounded. If this is
the case, verify that the Earth
Ground connection is valid and not
shared between multiple pieces of
equipment.
Configurable output - analog mode is
invalid
:
0–10 V output is set to 10–100%, but 0 V is at
output terminals.
Output is in protection mode
, a state the
analog portion of the configurable output
goes into when it detects a wiring problem.
The analog output is set to 0% regardless
of the command whenever a wiring fault is
detected.
Cause:
There is a power polarity mismatch between
the connected device and the configurable
output.
Correction:
Ensure polarities of ~24 V COM/OCOM
match and that the connected end device
uses the same polarity.
1. Measure the output and verify that it
matches the command.
2. Disconnect the connected device
and verify the commanded value is
present.
Configurable output - analog mode is
invalid
:
0–10V output has an undesirable offset of up
to 1 V.
The Common Reference is incorrect.
Cause:
The OCOM terminal is not connected.
Correction:
Connect the OCOM terminal of the
configurable output to the common of the
connected end device.
1. Measure the output and verify that it
matches the command.
2. Disconnect the connected device
and verify the commanded value is
present.
VMA1617 and VMA1632 VAV Controllers Installation Guide
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