Johnson Controls VMA1200 Series Troubleshooting Manual

Brand: Johnson Controls

Model: VMA1200 Series

Type: Troubleshooting Manual

ORKS

Systems Manual 1162

VMA1200 Section

Issue Date 0401

Code No. LIT-1162380

ECHNICAL

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.

ORKS



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

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.

ORKS

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

ORKS

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

ORKS

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

ORKS

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

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,

replace the diffuser with one designed for

low velocity,

install a series fan,

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:

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.

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).

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:

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

)

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:

Observe whether flexible duct is installed and connected to the

VAV box inlet.

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

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.

Within the M-Pro configuration file, verify that the AI setup is

defined properly.

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.

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).

Ensure that there are 3-5 duct diameters of straight ductwork

upstream of the airflow pickups.

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:

Recalibrate differential pressure by disconnecting the high and

low side tubing from the box pickup pressure taps.

Troubleshooting VMA1200 Series Controllers 17

Auto Calibrate the velocity pressure sensor by selecting Auto Zero

Pressure Sensor from the Balancing Action menu in the VBT

software.

Reconnect the high and low side tubing, ensuring the connections

are correct.

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:

Examine the pickup pressure taps inside the VAV box.

Check for plugged pickup ports and internal leaks between the

high and low pressure sides of the sensor.

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.

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:

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.

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

Room

Sensor

Room

Sensor

Crossed

Figure 3: Crossed Ductwork

Troubleshooting Balancer’s Flow Reading

To troubleshoot Balancer’s flow reading, perform the following test:

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.

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:

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.

Check if the primary voltage matches the transformer’s voltage

rating.

Check the 24 VAC cable length vs. wire gauge. For example, you

can only use 11 m (35 ft) of 1.5 mm

(18 AWG) wire at 100 VA.

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.

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.

Remove all the field wires and LONWORKS Network Bus wires

from the VMA, but leave the transformer wires attached.

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.

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.

www.johnsoncontrols.com

Controls Group FAN 1162

507 E. Michigan Street L

ORKS

Systems Manual

P.O. Box 423 Release 1.0

Milwaukee, WI 53201 Printed in U.S.A.

Johnson Controls VMA1200 Series Troubleshooting Manual

Johnson Controls VMA1200 Series Troubleshooting Manual

Johnson Controls VMA1200 Series Troubleshooting Manual

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