MUA Interlock Fault

MUA Interlock Fault


MUA Interlock Fault Summary

This guide is intended for contractors and licensed personnel.  Lock out Tag Out procedures and all other safety standards should be followed before working on any electrical equipment.  Reference the product manual (OIM) before proceeding.

Make Up Air (MUA) is the replacement air which feeds the exhaust hood through the plenums near or in front of the hood.  When the MUA is not functioning, the building may be in a negative air balance state, which can significantly impact the comfort in the kitchen and dining areas.  Negative air balance also impacts the hood's ability to capture smoke and effluent.

The MUA interlock fault may be present on systems where MUA fan proving is required.  It was commonly specified from approximately 2009 until 2024.

To reset this fault, simply unplug the J6 plug on the ECPM03 Board in the hood control panel and plug it back in.

The fault may also be cleared by installing a jumper between the D3 and D7 terminal blocks in the makeup air unit or IL1A and IL1B in the ECP.

Warning

This jumper may only be installed temporarily for troubleshooting purposes.

The jumper must be removed once the issue is corrected.

Failure to remove the jumper will result in the loss of notification of the MUA interlock failure

This will reset the fault and the ECP will make another attempt to enable the makeup air unit.

If the fault returns, there is still an issue present that is causing the fault.

MUA Interlock Fault Causes

The lists below are common causes for this fault. 
If it is determined that the fault is not being caused by any of the reasons below, there may be an underlying issue.

Faults during the installation process may be caused by any of the following:

  1. Interlock wiring between the hood controls (ECP) and MUA unit are missing and/or incomplete.
  2. Loose connections in the interlock wiring loop.
  3. No power ran to the makeup air unit.
  4. Make up air unit disconnect and/or circuit breaker are off.
  5. Interlock wiring landed incorrectly in ECP and/or makeup air unit.

            Factory wiring may be loose, incomplete, incorrect, etc.

Faults after commissioning may be caused by any of the following:

  1. The makeup air unit is in a freezestat lockout.
  2. The makeup air unit is in a flame lockout.
  3. The makeup air unit high temp limit is tripped.
  4. The makeup air unit intake damper is not opening.
  5. The makeup air unit intake damper end limit is not closing.
  6. The RE-DV relay in the makeup air unit has failed.
  7. The intake damper actuator in the makeup air unit has failed.
  8. The makeup air intake damper end limit switch is out of adjustment.
  9. Loose connections in the interlock wiring loop.
  10. The makeup air unit breaker and/or disconnect switch is off.
    1. This is common after hood system cleanings and/or service work.
Additional information regarding the MUA Interlock Fault can be found below.

The MUA Interlock fault occurs when the signal that is sent from the ECPM03 Board is not received back to the ECPM03 Board.
This low voltage signal is field wired to the makeup air unit terminal blocks D3 and D7 which are factory wired to the Common and Normally Open contacts on the RE-DV relay base.
Terminals IL1A and IL1B on the ECPM03 Board are the terminals which send and receive the signal.  The signal is low voltage/low current, and the ECPM03 board is simply looking for continuity.
  1. IL1A sends the signal from the ECPM03 Board to the RE-DV relay in the makeup air unit.
  2. IL1B on the ECPM03 Board receives the signal back from the RE-DV relay in the makeup air unit.


When the makeup air unit receives a start signal from the control package, the intake damper actuator in the makeup air unit is energized and begins to open the intake damper.
Once the intake damper is fully open, the end limit switch closes in the intake damper actuator and the RE-DV relay is energized with 120 VAC.
When the RE-DV relay is energized, this closes the connection between the Common and Normally Open relay contacts.
This allows the signal from IL1A on the ECPM03 Board to return to IL1B on the ECPM03 Board and the control package will allow the makeup air unit to run.
If this signal is not received back to IL1B on the ECPM03 Board, the control package HMI will display an MUA Interlock fault.


Notes
Wiring
The purpose of this interlock wiring is to allow the ECPM03 Board to prove that the makeup air unit damper is open.
If this wiring is incorrect and/or not completed, the ECP HMI will display an MUA Interlock fault.
Leaving the jumper in place between IL1A and IL1B will keep the MUA Interlock from being displayed.
However, this may also result in possible operation issues with the makeup air unit, as there will be no way for the ECPM03 Board to prove that the makeup air unit damper is open.

The ECPM03 Board will have a factory installed jumper between IL1A and IL1B.
This jumper will need to be removed so the wiring from the makeup air unit can be landed on these terminals.
There should be a factory provided drop in the makeup air unit that contains the yellow and red wires for the damper proving interlock when it is required.  Not all systems require this interlock.

 



On some jobs, there will be a second makeup air unit that needs to be interlocked to the ECP.
The damper proving interlock wiring for a second makeup air unit will utilize terminals IL2A and IL2B on the ECPM03 Board.
The terminals in the second makeup air unit will still be labeled as D3 and D7.
It is important to ensure that the wiring between each makeup air unit and the ECP does not become crossed as this may result in operational issues.




Notes
Troubleshooting
Many times this fault is caused by incorrect/incomplete field interlock wiring.
Factory wiring and component failure may also cause this issue but it is not common.

MUA units may be equipped with analog controls or digital controllers.
Troubleshooting will be similar but wiring schematics will be different.
Makeup air units designed to be interlocked with the ECP will be equipped with the RE-DV relay regardless of if they were built with old style or new style controls.
Connections between the ECP and makeup air unit will be the same as outlined in the Wiring section of this guide.
If an MUA Interlock fault is present, this means that the ECPM03 Board is not receiving the signal back to IL1B from IL1A.

1. Confirm that the makeup air unit disconnect switch and circuit breaker (CB-01) are in the ON position.
  1. Disconnect switches may vary in appearance and the ON and OFF positions are clearly marked.
  2. The circuit breaker (CB-01) switch should be UP and displaying a red indicator.


2. Once the disconnect switch and circuit breaker positions are confirmed, the fault will need to be reset
  1. This is done at the ECPM03 Board by unplugging the J6 connector and plugging it back in.
Alert
  1. Unplugging J6 will temporarily turn the lights and fans off if they are on.
    1. If the system was on by temp, operation should resume when J6 is plugged back in.
    2. If operation does not resume, press the light and fan button on the HMI to turn everything on again.
      

3. When the system reboots and the fans are turned on, monitor the HMI for the MUA Interlock fault.
  1. If the fault returns, double check all damper interlock wiring for loose connections, pinched wire insulation, broken wires, etc.
  2. See the Wiring section above to confirm that the field interlock wiring is properly connected between the ECP and makeup air unit.
Info
If all wiring is correct, the issue may be within the makeup air unit.

4. Remove the wires from IL1A and IL1B and install a jumper between them.
  1. A jumper can also be installed in the makeup air unit across terminal blocks D3 and D7.
  2. This will allow the ECP to provide the run command for the makeup air unit so troubleshooting can be done at the makeup air unit.

5. Clear the fault by following Step 2 and go to the makeup air unit.
  1. Be sure to take a multi-meter and screwdrivers to the makeup air unit.

6. Set your multi-meter to AC volts.
  1. For units with new controls (equipped with red MUA Board), check for 120 VAC across terminal blocks H and N.
    1. If 120 VAC is not present across terminal blocks H and N, refer back to the wiring section and Step 1.


  1. For units with old controls, (NOT equipped with red MUA Board) check for 120 VAC across terminal blocks 1 and N.
    1. If 120 VAC is not present across terminal blocks 1 and N, refer back to the wiring section and Step 1.

7. If there is 120 VAC present, visually inspect the intake damper and confirm that it is open.
  1. If the damper is open and the unit has new controls, measure AC voltage across terminals IEL and N.
  2. If 120 VAC is present, this proves that the damper actuator end limit switch is closed and the fan should be running.
  3. If 120 VAC is NOT present, inspect the damper end limit switch wiring for loose/improper connections.
    1. The damper end limit switch wires to terminal block H and IEL.

  1. If the damper is open and the unit has old controls, measure AC voltage across terminals 5 and N.
  2. If 120 VAC is present, this proves that the damper actuator end limit switch is closed and the fan should be running.
  3. If 120 VAC is NOT present, inspect the damper end limit switch wiring for loose/improper connections.
    1. The damper end limit switch wires to terminal block 2 and 5.


8. If the damper end limit switch is wired correctly and allowing voltage to pass through, the RE-DV relay should be checked for proper wiring and operation.
  1. Confirm the RE-DV relay is wired correctly per the wiring schematic.
  2. If wiring is correct, the RE-DV relay should have a red illuminated LED when energized.
  3. Coil voltage can also be confirmed.
    1. Terminal 7 and 8 on the relay base are the coil terminals.
      1. Terminal 7 on the relay base to terminal block N should read 120 VAC.
      2. Terminal 8 on the relay base to terminal block N should also read 120 VAC.
      3. If voltage is not present on either coil terminal, there may be an issue with the relay and/or relay socket and may need to be replaced.
  4. If the relay LED is illuminated and coil voltage is correct, check for proper wiring and operation of the relay contacts.
    1. As previously stated in this guide, the damper proving interlock signal from IL1A is routed through the Common and Normally Open contacts of the RE-DV relay and back to IL1B on the ECPM03 Board.
      1. The D3 terminal block in the makeup air unit should be wired to Common on the RE-DV relay base.
      2. The D7 terminal block in the makeup air unit should be wired to Normally Open on the RE-DV relay base.




9. Once all wiring and component operation is confirmed, The jumper between IL1A and IL1B on the ECPM03 Board can be removed and the wires from the makeup air unit can be reconnected.

10. If the fault reappears, follow Step 2 to reset it.

Info
All of the above information outlines general and common methods to correct an MUA Interlock Fault.
If all of the provided information checks out and the fault persists, please contact our technical support department.
You can also create a technical support ticket here Submit A Ticket.