Johnson Controls VMA1200 Series Troubleshooting Manual
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Johnson Controls VMA1200 Series Troubleshooting Manual

Johnson Controls VMA1200 Series Troubleshooting Manual

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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.
© 2001 Johnson Controls, Inc.
Code No. LIT-1162380
T
B
ECHNICAL
ULLETIN
L
W
Systems Manual
ON
ORKS
VMA1200 Section
Issue Date
www.johnsoncontrols.com
1162
0401

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  • Page 1: Table Of Contents

    1162 ORKS VMA1200 Section Issue Date 0401 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...
  • Page 2 VMA1200...

  • Page 3: Troubleshooting Vma1200 Series Controllers

    Troubleshooting VMA1200 Series Controllers 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.

  • Page 4: Key Concepts

    VMA1200 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.

  • Page 5: Hardware Concerns

    Troubleshooting VMA1200 Series Controllers 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.
  • Page 6 VMA1200 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.

  • Page 7: Vma Control Performance Measures (Diagnostics)

    Troubleshooting VMA1200 Series Controllers 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.
  • Page 8 VMA1200 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.
  • Page 9 Troubleshooting VMA1200 Series Controllers 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.
  • Page 10 VMA1200 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. Network Bus Communication Problems ORKS Network Bus communications problems between the...

  • Page 11: Procedure Overview

    Troubleshooting VMA1200 Series Controllers Procedure Overview Table 1: Troubleshooting VMA System Operation Procedure Overview To Do This Follow These Steps: Investigate Occupant Hot/Cold Check symptom/cause/action (Table 2). Complaints Troubleshoot Airflow and Troubleshoot airflow leakage at a fully closed damper. Temperature Problems Troubleshoot low air velocity.

  • Page 12: Detailed Procedures

    VMA1200 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.
  • Page 13 Flow greater than Mounting the VMA section in the Mounting Space Greater than sq ft Box Area * 40.) and Wiring VMA1200 Series Controllers 1°C (2°F) Technical Bulletin [LIT-1162360]); or decrease minimum flow setpoint; or check for differential pressure sensing problem.

  • Page 14: Troubleshooting Airflow And Temperature Problems

    VMA1200 Symptom (Cont.) Cause Action Occupant Cold Zone sensor placement See the Room Sensor Placement section in Complaints or EWMA resulting in non-representative the Variable Air Volume Modular Assembly Space Greater than temperature sensed (VMA) 1200 Series Overview and 1°C (2°F) Engineering Guidelines Technical Bulletin (Cont.) (LIT-1162350).
  • Page 15 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.
  • Page 16 VMA1200 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.
  • Page 17 Troubleshooting VMA1200 Series Controllers 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.
  • Page 18 VMA1200 Room Room Sensor 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.

  • Page 19: Detecting Problems Using Vma Leds

    Troubleshooting VMA1200 Series Controllers 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...

  • Page 20: Verifying Proper Transformer Installation

    VMA1200 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.

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