Troubleshooting - Metasys - MS-VMA1826-x - MS-VMA1832-x - Field Device - VMA18 VAV Modular Assembly

VMA1826/1832 VAV Controller Installation Guide

Product name
VMA18 VAV Modular Assembly
Document type
Installation Guide
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Document revision
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Table 1 provides LED status indicator information for troubleshooting the VMA 18 controller.
Note: If you experience short circuits in the 24 VAC power supply causing protective devices such as breakers or fuses to trip, make sure that the power connections on the VMA are not reversed. The most common cause of this problem is when the 24 VAC power supply on the VMA is reversed but not reversed on a connected secondary device. Improper wiring of this power terminal may cause a short circuit across the 24 VAC power supply on -1 models.
Table 1. Troubleshooting
Problem Possible cause Correction Verification
Controller is Off Power at Primary of Transformer, 0V at Secondary Transformer has tripped
  1. Transformer is shorted
  2. 24VAC 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
  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, 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
  1. Disconnect the secondary of the 24 VAC transformer
  2. Use an ohm-meter to measure between ~24 V HOT and COM; there should be no short circuit
Power at Primary of Transformer, 24 V at Secondary, 0V at Fuse/Breaker Breaker/Fuse has tripped
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 Power polarity mismatch between connected device and configurable output 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
0–10V output has an undesirable offset of up to 1V Common Reference is incorrect OCOM terminal is not connected Connect OCOM terminal of the configurable output to the common of the connected end device