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Systems Manual 1162
VMA1200 Section
Issue Date 0401
© 2001 Johnson Controls, Inc. www.johnsoncontrols.com
Code No. LIT-1162380
T
ECHNICAL
B
ULLETIN
Troubleshooting VMA1200 Series Controllers
Troubleshooting VMA1200 Series Controllers ...................................3
Introduction........................................................................................................*3
Key Concepts...................................................................................................... 4
Troubleshooting Tools......................................................................................................*4
Hardware Concerns .........................................................................................................*5
VMA Control Performance Measures (Diagnostics) ........................................................*7
Procedure Overview......................................................................................... 11
Detailed Procedures......................................................................................... 12
Investigating Occupant Hot/Cold Complaints.................................................................*12
Troubleshooting Airflow and Temperature Problems.....................................................*14
Detecting Problems Using VMA LEDs ...........................................................................*19
Verifying Proper Transformer Installation.......................................................................*20
Checking for Proper Device Isolation and Ground Loops ............................................... 20
* Indicates those sections where changes have occurred since the last printing.
VMA12002
Troubleshooting VMA1200 Series Controllers 3
Troubleshooting VMA1200 Series
Controllers
Introduction
Although the Variable Air Volume Modular Assembly (VMA) has
been designed to provide reliable service, problems can develop in the
related building and HVAC (Heating, Ventilating, and Air
Conditioning) systems that affect VMA performance. Problems
usually surface in the form of occupant comfort issues or
communication failures. The causes of these problems range from
device failures to HVAC system maintenance and design issues, to
installation errors, or to changes in use of a zone. Consider all of these
variables when troubleshooting.
This document discusses the indicators, tools, and procedures available
to troubleshoot systems employing the VMA. This document describes
how to:
● investigate occupant hot/cold complaints
● troubleshoot airflow and temperature problems
● detect problems using VMA Light-Emitting Diodes (LEDs)
● verify proper transformer installation
● check for proper device isolation and ground loops
VMA12004
Key Concepts
Troubleshooting Tools
Building Automation System (BAS)
The Metasys BAS gives access to VAV (Variable Air Volume)
system operation. Using the information available though Focus
windows (either Direct Map or Control System [CS] objects), data from
a malfunctioning system can be monitored to help problem analysis and
resolution.
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Network Management Tools
LONWORKS network management tools provide additional
diagnostics. These third-party tools also allow you to make parameter
changes to correct temperature and airflow control problems.
Refer to the user’s manual of the specific network management tool
for more information.
Comm Pro Commissioning Tool
The Comm Pro commissioning tool is software that allows users to
view and modify device parameters to correct temperature and airflow
control problems. It also allows users to download new firmware to the
controller. Comm Pro software is part of M-Tool and can be launched
from M-Pro. For more information, refer to Comm Pro User’s Guide
(LIT-1162550).
VMA1200 Balancing Tool (VBT) Software
The VBT software helps you balance VAV systems with VMA1200
Series controllers. The software runs on a Palm compatible handheld
device (Version 2.0 or higher operating system). The VBT commands
the VMA to desired flow setpoints, temporarily overrides some
outputs, and corrects configuration properties (parameters) stored in
the VMA. For more information, refer to Using the VMA1200
Balancing Tool (VBT) Software Technical Bulletin (LIT-1162400).
Troubleshooting VMA1200 Series Controllers 5
Hardware Concerns
Temperature Problems
Zone temperature sensor errors cause control problems. The AI range
may be improperly selected in the M-Pro software used to configure
the VMA1200. The temperature sensor may need an offset for cable
length. In addition, the temperature sensor may be improperly installed
or the element may be damaged. The temperature sensor may be
placed where it is affected by the sun, other zones, or supply air from
the diffuser. Refer to Variable Air Volume Modular Assembly (VMA)
1200 Series Overview and Engineering Guidelines Technical
Bulletin (LIT-1162350) for other sensor location issues.
Airflow Problems
The VMA auto calibrates the pressure sensor within the first hour after
power up and then periodically every two weeks (default is every
336 hours), to correct offset tolerance and effects of mounting
position. If greater flow measurement accuracy is required at low flow
rates where box inlet velocity is under 1.25 m/s (250 fpm), the Auto
Calibration Period can be decreased. Remember that during Auto
Calibration, the damper is commanded to fully close and the
airflow to the zone drops to zero for up to 3 minutes.
Refer to the VMA Airflow Rate section of the Variable Air Volume
Modular Assembly (VMA) 1200 Series Overview and Engineering
Guidelines Technical Bulletin (LIT-1162350) for more information.
Damaged damper seal, bent damper blades, poorly designed dampers,
or a misaligned actuator at end of travel causes air leakage during the
fully closed position. This causes offset errors during the pressure
sensor calibration.
Control problems can result from a slipping damper shaft or an
obstruction that causes the actuator to stall. If the damper overrotates,
control problems occur. You must provide fixed end stops at each end;
one where the damper is fully closed, and one at the fully open
position. For 90° boxes, the stops are built into the VMA. For 45° and
60° boxes, the VMA must be installed with the damper either fully
open or fully closed to provide its end stop.
VMA12006
Ductwork Design Issues
Air velocity is non-uniform if turns or transitions in rigid duct, or sags
in flexible duct are within close proximity to the flow pickups. In this
case, the pickup ports may not represent the true average air velocity.
A minimum of three duct diameters of straight, unrestricted duct,
upstream from the airflow pickups is recommended. Correct flow
reading problems by installing straightening vanes in a duct section or
changing the duct configuration to provide greater separation between
the transition and the pickup.
Long duct length or sags in flexible duct cause significant pressure
drop. Avoid this by installing rigid duct three times the diameter in
length, starting at the VAV box inlet.
Flow Pickup Performance
The flow pickup must be installed properly. Poor installation causes
debris collection, plugged ports, or leaks between the high and low
pressure manifold.
Air Flow
Tota l Pr ess ur e
Static Pressure
Static Pressure
Pickup
High Pressure
Manifold
Pickup
Low Pressure
Manifold
Area of Increased
Velocity and
Decreased Pressure
Duct Wall
Pickup
Figure 1: Interaction of the Pickup and Air Stream
As shown in Figure 1, the pickups must have openings that are
perpendicular to the direction of flow. The low pressure ports face
downstream, and the passing air exerts a pull on these openings,
causing a pressure less than static. This results in an airflow pickup
gain, and a differential pressure of 1.5 to 3 times the velocity pressure.
Figure 2 shows typical flow pickup designs. Usually the cross and ring
types perform better than straight tubes because the sensing ports are
better distributed across the duct area.
Troubleshooting VMA1200 Series Controllers 7
Sensing Ports
Cross Tubes Squared Rings Straight Tubes
Sensing
Figure 2: Common Flow Pickups
VAV Box Size
The size and capacity of the VAV box should match the zone loads.
If the installed box is too small, insufficient cooling results and audible
noise caused by high flow rates is emitted. If the installed unit is
too large, proper control of airflow is difficult.
The VAV box area and flow pickup gains must be entered into the
VMA1200 for the controller to accurately calculate airflow. Enter
these values during either configuration or commissioning.
VMA Control Performance Measures (Diagnostics)
Temperature Control Measures
Key network variables that indicate temperature control problems are:
nvoEwmaSpace (network variable output Exponentially Weighted
Moving Average Space). This is an average of the zone temperature
control loop error (setpoint minus temperature) over the preceding
eight hours of control in normal control modes. This calculation is
stopped in all modes except heat and cool. If the VMA is interlocked
with supply air availability, and the zone is well designed, this
measure should always be within +/-0.5°C (+/- 1°F). Since controller
error is defined as setpoint minus process variable feedback, negative
numbers indicate a warm zone and positive values indicate a cold
zone.
nvoEwmaAbsSpace. This is an average of the absolute value of space
temperature error (absolute value of setpoint minus temperature) over
the preceding eight hours of control. This calculation is stopped in all
modes except heat and cool. It is just like the nvoEwmaSpace, except
that the error is always considered positive. If the VMA is interlocked
with supply air (fan) availability, and the zone is well designed, this
measure should always be less than 0.5°C (1°F). Larger values
VMA12008
indicate a cooling or heating problem, a cycling control, or an
extended cooldown/warmup in progress.
Airflow Control Measures
Key network variables that indicate airflow control problems are:
nvoEwmaFlow. This is an average of the flow control loop error
(setpoint minus calculated flow) over the preceding 20 minutes of
control in normal control modes. This calculation is stopped during
morning warmup or when the Heat/Cool mode is off.
Increasing positive values indicate a starved box. Negative values
indicate a stuck damper or stalled actuator.
nvoEwmaAbsFlow. This is an average of the absolute or unsigned
flow control loop error (difference between setpoint and measured)
over the preceding 20 minutes of control in normal control modes.
This calculation is stopped during morning warmup or when the Heat
Cool mode is off.
Delta P Status. If the sensed value of the velocity pressure (Delta P)
sensor is outside of the normal operating range for several readings,
the Present Value of Flow Loop is unreliable. An open or short in the
sensor normally causes this condition. This status is available in the
Alarm field of the nvoUnitStatus variable.
nvoMvgAveDutyCyc. This is the duty cycle of the damper. It
measures the performance of the damper output. A large value
indicates that the flow controller is having problems controlling.
nvoMvgAveRev. This is the number of reversals of the damper
output. It measures the performance of the damper output. A large
value indicates that the flow controller is having problems controlling.
Troubleshooting VMA1200 Series Controllers 9
Balancing Errors
Pressure independent VAV control jobs frequently require a flow
accuracy of 5-10%. The balancing contractor must adjust and certify
the flow rates specified by the consulting engineer.
When actual vs. measured airflow readings disagree, a problem exists
in the measurement equipment used by the controller, as well as that
used by the Balancer. Therefore, it is important that both the controls
contractor and Balancer understand the equipment, techniques, and
expectations of each other.
Typical factors that contribute to Balancer flow reading errors include:
•
Not calibrating the flow hood as specified. Flow hood accuracy is
specified by the manufacturer and is anywhere from ±5% of full
scale to ±3% of reading on better instruments. A dated calibration
certificate shows the last calibration.
•
Calibrating the flow hood on a different type of diffuser other than
that used on the job.
•
Using multiple diffusers supplied by a single VAV box. When the
flow hood is placed over one diffuser, the hood presents a
restriction, causing less flow from the measured diffuser and more
flow from the others. In this case, the Balancer’s sum of the
readings taken at all diffusers served by the box is less than the
actual total flow.
•
Performing airflow measurements using a hood rather than a
velocity probe type of instrument with a slotted diffuser. Tests
show that hood readings of some slotted diffusers are as much as
40% erroneous. The diffuser manufacturer’s literature specifies
how to measure airflow and what instrument to use.
•
Incorrectly mounting the balancing damper. If mounted directly on
the diffuser, turbulent flow patterns entering the hood may occur,
resulting in erroneous hood indication.
•
Mismatching the flow hood with the diffuser size such that the
diffuser is not completely covered.
The Balancer may take two additional measurements to help find the
cause of flow reading discrepancies:
•
Verifying the controller differential pressure reading with a high
accuracy differential pressure meter.
•
Performing a duct traverse as detailed in 1993 ASHRAE Handbook
Fundamentals, I-P Edition, 13.14-15.
VMA120010
VMA LED Indicator Status
The VMA LED provides general diagnostics for VMA power supply
and operating status. Viewing the LED signal and understanding what
each type of signal indicates quickly isolates some problems. See the
Detecting Problems Using VMA LEDs section for details.
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Network Bus Communication Problems
LONWORKS Network Bus communications problems between the
VMA and the supervisory system are related to improper installation,
configuration errors, or both.
Typical communications problems include:
•
broken or frayed wire
•
internally shorted device
•
too many devices (64 maximum per segment allowed)
•
LONWORKS Network Bus too long
•
ground loops--The L
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Network Bus shield, if used, must
be earth grounded at only one location (usually the NCM). The
LON+ and LON- lines are never earth grounded. Tie the shield to
the SHLD terminal on the L
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Network connector of the
VMA.
•
missing, improperly located, or wrong value of end of line
terminators
Zone Bus Problems
If a communication error occurs while using the commissioning tool
with the VMA over the Zone Bus, the cause is often a loose or
improper connection between the CablePRO (AS-CBLPRO) or
CVTPRO (AS-CVTPROx00-0), the Palm compatible handheld device,
and the controller. Low batteries on the handheld device could also be
at fault.
The Zone Bus LEDs on the CablePRO or CVTPRO blink only when
sending or receiving data from the handheld device. The handheld
device only sends or receives data when it synchronizes with the VMA
or upon a command.
An effective troubleshooting technique is to observe the LEDs on
either a CVTPRO converter or a CBLCON cable connector
(AS-CBLCON). The red LED indicates power from the VMA and the
green LED indicates that the Zone Bus is present. With no handheld
device connected to the Zone Bus, the green LED blinks once every
second. When a handheld device is communicating, the LED blinks
several times per second.
Troubleshooting VMA1200 Series Controllers 11
Procedure Overview
Table 1: Troubleshooting VMA System Operation Procedure Overview
To Do This Follow These Steps:
Investigate Occupant Hot/Cold
Complaints
Check symptom/cause/action (Table 2).
Troubleshoot Airflow and
Temperature Problems
Troubleshoot airflow leakage at a fully closed damper.
Troubleshoot low air velocity.
Correct distorted flow patterns due to duct design.
Correct unreliable sensor readings.
Check flow problems by verifying velocity pressure sensor operation.
Check airflow pickups for debris or water.
Check for miswired temperature sensors and misapplied room
assignments.
Troubleshoot Balancer’s flow reading.
Detect Problems Using VMA
LEDs
Use the LED to help pinpoint the problem. Refer to the LED Response
tables (Tables 3 and 4).
Verify Proper Transformer
Installation
Connect the DMM (digital voltmeter) across the 24 VAC terminals of the
VMA. Read the voltage with loads energized. A reading of 24-27 VAC is
required. If you read a value less than 22 VAC, the circuit is improperly
installed or overloaded.
Check if the primary voltage matches the transformer’s voltage rating.
Check the 24 VAC cable length vs. wire gauge.
Recalculate the VA requirements for the VMA and transformer loads.
Check for Proper Device
Isolation and Ground Loops
Connect the leads of the DMM in parallel with the 100K ohm resistor from
the DC power supply (+15 VDC) output terminal of the VMA to earth
ground. If you measure less than 5 VDC/VAC, the circuit is isolated.
If not:
Remove all the field wires and L
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Network Bus wires from the
VMA.
Reconnect each field wire set one at a time until you read 5 VDC/VAC or
greater.
Correct the problem. All grounds are corrected when you read less than
5 VDC/VAC on the DMM.
VMA120012
Detailed Procedures
Investigating Occupant Hot/Cold Complaints
Zone temperature control problems, which are usually reported as
occupant hot/cold complaints, have causes ranging from the building
or mechanical system to the control components. The following guide
helps you locate the cause of zone temperature control problems with
pressure independent VAV terminals.
Table 2: Occupant Hot/Cold Complaints
Symptom Cause Action
Occupant Hot Complaints
Zone setpoint too high Lower the common setpoint, or
calibrate remote setpoint potentiometer.
Controller not in Occupied
mode
Check to see if mode is commanded by
network features.
Setpoint offset Set Occupied setpoint offset to one degree
or less for greatest comfort.
Occupant Hot Complaints
or EWMA Space Less
than -1°C (-2°F)
Insufficient airflow Check terminal box inlet obstructions.
Airflow not in control (Indicated
by nvoEwmaFlow greater than
m
2
Box Area * 200 [l/s] or
sq ft Box Area * 40 [cfm])
Tighten damper shaft coupling, or
increase minimum flow setpoint, or
reconnect duct, or look for a
differential pressure sensing problem.
Reheat and or supplemental
heat stuck on, valve stuck open
or wrong stroke time/range
Verify heating device operation.
Verify reverse or direct acting valves.
VAV box inlet air too warm
With the box at maximum cooling flow, verify
diffuser air temperature is 10 to 15°C
(50 to 60°F). Warmer air temperature may
indicate supply air temperature problem,
stuck reheat valve or box series fan adjusted
to flow higher than maximum cooling.
Zoning problem - VAV box
serves multiple rooms/areas
See the Establish Zones section in the
Variable Air Volume Modular Assembly
(VMA) 1200 Series Overview and
Engineering Guidelines Technical Bulletin
(LIT-1162350).
Zone sensor placement
resulting in non-representative
temperature sensed
See the Room Sensor Placement section in
the Variable Air Volume Modular Assembly
(VMA) 1200 Series Overview and
Engineering Guidelines Technical Bulletin
(LIT-1162350).
Zone sensor wiring crossed Rewire VMA to appropriate sensor.
VAV outlet duct crossed Change duct routing or cross sensor wiring.
Cooling load exceeds design
due to change in use, added
equipment, or people
Investigate possibility of increasing the Max
Cooling Flow setpoint. (How much greater is
present load than design? Is sufficient
supply air available? Is box large enough?)
Continued on next page . . .
Troubleshooting VMA1200 Series Controllers 13
Symptom (Cont.) Cause Action
Occupant Cold
Complaints
Zone setpoint too low Raise the common setpoint, or
calibrate remote setpoint potentiometer.
Controller not in Occupied
mode
Check to see if mode is commanded by
network features.
Occupied setpoint offset too
large
Set offset to 1 degree or less for greatest
comfort.
Occupant Cold
Complaints or EWMA
Space Greater than
1°C (2°F)
Airflow not in control (Indicated
by nvoEWMA Flow greater than
sq ft Box Area * 40.)
Tighten damper, shaft coupling (refer to the
Mounting the VMA section in the Mounting
and Wiring VMA1200 Series Controllers
Technical Bulletin [LIT-1162360]); or
decrease minimum flow setpoint; or check
for differential pressure sensing problem.
Refer to the VMA Airflow Rate section of the
Variable Air Volume Modular Assembly
(VMA) 1200 Series Overview and
Engineering Guidelines Technical Bulletin
(LIT-1162350).
Too much airflow
Often due to minimum airflow when zone is
not occupied. Set minimum airflow lower, or
an occupancy sensor may help.
VAV box inlet air too cold Supply air temperature too low
(10 to 15°C [50 to 60 °F] typical).
When most boxes are operating near their
minimum cooling flow, use network features
to reset supply air temperature to a higher
level.
Reheat and or supplemental
heating media not available
Often caused by disabling heating based on
arbitrary means like calendar dates. Use
network features to enable heating based on
demand (nviHeating avail.).
Reheat media temperature too
low
If reheat water temperature is too low, or
airflow is too great, zone will not warm.
Verify water temperature and airflow against
design specifications.
Cold spots or drafts due to low
velocity air dropping on
occupants
Raise the supply air temperature,
or
replace the diffuser with one designed for
low velocity,
or
install a series fan,
or
control a parallel fan from flow rather than
temperature.
Reheat and or supplemental
heat stuck off or valve stuck
closed or wrong stroke time or
range
Verify heating device operation.
Zoning problem - VAV box
serves multiple rooms/areas
See the Establish Zones section in the
Variable Air Volume Modular Assembly
(VMA) 1200 Series Overview and
Engineering Guidelines Technical Bulletin
(LIT-1162350).
Continued on next page . . .
VMA120014
Symptom (Cont.) Cause Action
Occupant Cold
Complaints or EWMA
Space Greater than
1°C (2°F)
(Cont.)
Zone sensor placement
resulting in non-representative
temperature sensed
See the Room Sensor Placement section in
the Variable Air Volume Modular Assembly
(VMA) 1200 Series Overview and
Engineering Guidelines Technical Bulletin
(LIT-1162350).
Zone sensor wiring crossed Rewire VMA to appropriate sensor.
VAV outlet duct crossed Change duct routing or cross sensor wiring.
Heating load exceeds design
due to change in use or less
equipment and lights or fewer
people
Investigate possibility of decreasing the Occ
Cooling Flow setpoint (How much ventilation
is needed for the occupants?).
Troubleshooting Airflow and Temperature Problems
Use the following tests to troubleshoot factors that contribute to
controller flow or temperature inaccuracies. They include:
•
troubleshoot airflow leakage at a fully closed damper
•
troubleshoot low air velocity
•
correct distorted flow patterns due to duct design
•
check flow problems by verifying actuator operation
•
correct unstable sensor (AI) readings
•
check flow problems by verifying velocity pressure sensor
operation
•
check airflow pickups for debris and water
•
check for miswired sensors and misapplied room assignments
•
troubleshoot Balancer’s flow reading
•
verify VAV box and flow multiplier calculations
•
verify setpoints
Troubleshooting VMA1200 Series Controllers 15
Troubleshooting Airflow Leakage at a Fully Closed Damper
To troubleshoot airflow leakage at a fully closed damper, perform the
following test:
1.
Check damper stop positions. Refer to the Mounting and Wiring
VMA1200 Series Controllers Technical Bulletin (LIT-1162360).
On a 90° box, install at the closed position.
2.
Check that the actuator collar (or other linkage) is tightly locked
to the damper shaft. Refer to the Mounting and Wiring VMA1200
Series Controllers Technical Bulletin (LIT-1162360).
3.
Inspect for a damaged damper seal, bent damper blades, or a
poorly designed damper. Replace if necessary.
Troubleshooting Low Air Velocity
To troubleshoot low air velocity, perform this test:
1.
Check airflow velocity (1.25 m/s [250 fpm] is minimum) using
Comm Pro software or a LONWORKS Network Services (LNS)
network management tool.
nvoAirFlow (cfm)
> 1.25 m/s or 250 fpm
Cp Box Area (sq ft)
If measuring airflow in liters per second (l/s), substitute the
following equation:
nvoAirFlow (l/s) * 0 .001
> 1.25 m/s
Cp Box Area (m
2
)
2.
Check whether the flow is due to an oversized box. If so, check
with the Balancer to determine if adjusting the box constant via
M-Pro software or other system changes are reasonable.
Correcting Distorted Flow Patterns Due to Duct Design
To correct distorted flow patterns due to duct design, perform the
following test:
1.
Observe whether flexible duct is installed and connected to the
VAV box inlet.
2.
Whether hard or flexible duct is installed, check whether there is a
duct transition less than three diameters upstream of the airflow
pickups.
Note: Design conditions discussed in Steps 1 and 2 can cause
non-uniform air velocity across the flow pickup location.
VMA120016
3.
To eliminate turbulent flow problems, install a three diameter
length of straight rigid duct between the VAV box inlet and the
flexible duct (or duct transition).
Note. Excessive inlet duct length may also result in pressure drops
that restrict airflow.
Correcting Unstable Sensor Readings
To correct unstable sensor readings, perform the following tests.
1.
Within the M-Pro configuration file, verify that the AI setup is
defined properly.
2.
Check sensor calibration. Verify that the input reading is the same
as your standard. For temperature readings, a glass thermometer
with 0.05°C (0.1°F) accuracy is necessary. Adjust the AI offset in
the Attribute Data. For velocity pressure readings, ensure that
Auto Calibration is run from the VBT, and then verify flow
readings within 5% of balancing hood reading.
3.
Use Comm Pro software or an LNS network management tool to
verify that the AI point is reading steady. Unstable flow can be
due to turbulence in the duct. For a list of network variable names,
see the Variable Air Volume Modular Assembly (VMA) 1200
Series Controllers Application Note (LIT-1162500).
4.
Ensure that there are 3-5 duct diameters of straight ductwork
upstream of the airflow pickups.
5.
If AI point is still unstable, check the sensor for the following
problems:
•
Is the wrong type sensor installed or is it installed improperly?
•
Is the averaging element securely fastened?
•
Are the wires secure?
Checking Flow Problems by Verifying Velocity Pressure
Sensor Operation
To ensure accurate readings of the velocity pressure sensor, allow at
least thirty minutes stabilization time before installing a product that
just came from a storage environment that differs from the installed
environment.
To check flow problems by verifying velocity pressure sensor
operation, perform the following test:
1.
Recalibrate differential pressure by disconnecting the high and
low side tubing from the box pickup pressure taps.
Troubleshooting VMA1200 Series Controllers 17
2.
Auto Calibrate the velocity pressure sensor by selecting Auto Zero
Pressure Sensor from the Balancing Action menu in the VBT
software.
3.
Reconnect the high and low side tubing, ensuring the connections
are correct.
4.
Check flow by using the VBT software to drive to the Balancer’s
requested flow from the Balancing Action menu.
Checking Airflow Pickups for Debris or Water
!
WARNING: Equipment Damage Hazard. Never blow into
the VMA tubing. The velocity pressure
transducer is very sensitive and is destroyed by
as little as 1 psi/70 mbar of pressure.
To check airflow pickups for debris or water, perform the following
test:
1.
Examine the pickup pressure taps inside the VAV box.
2.
Check for plugged pickup ports and internal leaks between the
high and low pressure sides of the sensor.
3.
Disconnect the high and low tubes between the VMA and box
pickup pressure taps to observe if there is water or condensation
disrupting the pressure reading. If necessary, clear water from the
tubes and reconnect. Make sure tubes have low spot to collect
water.
4.
Perform Auto Calibration to adjust for any changes in the offset of
the output of the pressure sensor.
Checking for Miswired Temperature Sensors and
Misapplied Room Assignments
To check for miswired temperature sensors and misapplied room
assignments, perform the following test:
1.
If you are experiencing problems with poor control, check that the
room temperature sensor is connected to the correct VMA.
Sometimes sensors are miswired to an adjoining room’s VAV
box.
2.
Check that the VMA is controlling the right room. Crossed
ductwork commonly leads to mistakes similar to the one shown
in Figure 3.
VMA120018
VMA
VMA
Room
Sensor
Room
Sensor
Crossed
Figure 3: Crossed Ductwork
Troubleshooting Balancer’s Flow Reading
To troubleshoot Balancer’s flow reading, perform the following test:
1.
Determine if you are experiencing a discrepancy of more than
5 to 10% between the controller’s flow (nvoAir Flow) and
Balancer’s measured flow.
2.
If so, work with the Balancer to recalculate the pickup gains for
the VAV Box Calculation. The defaults are 2.25 for Gain-1,
and 0 for Gain-2.
Troubleshooting VMA1200 Series Controllers 19
Detecting Problems Using VMA LEDs
Use the VMA LEDs to help to determine the source of the power,
application or network configuration problem. See Tables 3 and 4 for
details.
Table 3: Checking Performance with the VMA LEDs
Color Name State Description
Off Controller is operating properly (lights
momentarily on power up).
Blinking
The network table is not configured.
Use Comm Pro software or a network
management tool to configure the
controller.
3 Blinks
then Off
Response to Wink command from VBT,
Comm Pro, or an LNS tool.
Red
Service
LED
On Controller problem. Download new
firmware code.
Table 4: Running LED
Color Name State Description
Blinking Application is running normally, LED
blinks at one second interval.
On steady Application is not running. Try the
following:
1. Check the power.
2. Download a new application.
If Steps 1 and 2 do not resolve the
problem, replace the VMA controller.
Green
Running
LED
Off steady Application is not running. Try the
following:
1. Check the power.
2. Download a new application.
If Steps 1 and 2 do not resolve the
problem, replace the VMA controller.
VMA120020
Verifying Proper Transformer Installation
Follow these steps to verify proper transformer installation:
1.
Connect the DMM across the 24 VAC and the 24 VAC common
terminal of the VMA. Read the voltage with all typical loads
energized. A reading of 24-27 VAC is required when the line
voltage is nominal. If you read a value less than 22 VAC, there is
too much load on that transformer or the line length is too long.
Split the load and add another transformer.
2.
Check if the primary voltage matches the transformer’s voltage
rating.
3.
Check the 24 VAC cable length vs. wire gauge. For example, you
can only use 11 m (35 ft) of 1.5 mm
2
(18 AWG) wire at 100 VA.
4.
Recalculate the VA requirements for the VMAs and loads on that
transformer.
Checking for Proper Device Isolation and Ground Loops
Use the following test to determine whether the VMA, field devices,
and the transformer are properly isolated.
1.
Connect the leads of the DMM in parallel with the 100K ohm
resistor from the DC power supply (+15 VDC) output terminal of
the VMA to earth ground.
Note: If you read less than 5 VDC/VAC, the circuit is properly
isolated. If not, follow Steps 2 through 4.
2.
Remove all the field wires and LONWORKS Network Bus wires
from the VMA, but leave the transformer wires attached.
3.
With the DMM still connected, reconnect each set of field wires
one at a time until you read 5 VDC/VAC or greater. At this point,
you have discovered one cause of the ground loop.
4.
Correct the problem. Continue to reconnect each set of field wires
until all ground loops are found and corrected. All grounds are
corrected when you read less than 5 VDC/VAC on the DMM.
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ORKS
Systems Manual
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