Johnson Controls MS-VMA1615-0U, Installation Instructions Manual, Page: 18 / 21

Table 7: Troubleshooting
Verification Correction Possible Cause Problem
Transformer has tripped Power at Primary of
Transformer, 0V at
Secondary Controller is Off 1. 1. 1. Disconnect the
secondary of the 24
VAC transformer Ensure polarity of ~24 V COM /
ICOM / + 15VCOM/SA BUS
COM on the controller, auxiliary
devices and I/O is the same. Transformer is shorted
2. 24VAC powered sensor is not
wired with the same polarity as
the controller
Breaker/Fuse has tripped. Power at Primary of
Transformer, 24 V at
Secondary, 0V at
Fuse/Breaker.
2. Use an ohm-meter to
measure between ~24 V
HOT and COM; there
should be no short
circuit.
2. Ensure OUT1-OUT3 terminals
of binary outputs are not
connected to ~24 VAC COM,
verify that OCOM1-OCOM3 are
not connected to ~24 VAC HOT
(these terminals are internally
sourced).
3. SA bus device is not wired with
the same polarity as the
controller
Note: Note that 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.
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.
Ensure polarities of ~24 V
COM/OCOM match and that the
connected end device uses the
same polarity. Power polarity mismatch between
connected device and configurable
output 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. 0–10 V output is set
to 10–100%, but 0 V
is at output terminals Configurable output
- analog mode is
invalid. 1. Measure the output and
verify that it matches the
command.
2. Disconnect the
connected device and
verify the commanded
value is present.
Connect OCOM terminal of the
configurable output to the common
of the connected end device. OCOM terminal is not connected Common Reference is
incorrect 0–10V output has an
undesirable offset of
up to 1 V
18 VMA1615 and VMA1630 Variable Air Volume Controllers Installation Instructions