CMU: The Basics of the MAC Board
Neptronic's Make-Up Air Controller, referred to as MAC, serves as a fundamental component within our innovative Compact Make-Up Air Unit (CMU).
The MAC board, which can be called the brain of the CMU, helps the system in enhancing the Indoor Air Quality (IAQ) by delivering air that is fresh, filtered, and pre-heated through ductwork. While the technical specifications of the CMU, such as airflow requirements and heating capacities, are pivotal in selecting the appropriate model for a given application, the effectiveness of these units ultimately relies on their control strategies.
This article discusses the standard features of the CMU by delving into the MAC board's basic control capabilities.
MAC Board Layouts
Diagrams illustrating the terminal connections for MAC1, MAC2, MAC3, and MAC4 boards:
MAC1/MAC2/MAC3/MAC4 Boards:
Each board features multiple terminal blocks (e.g., TB1, TB2, TB3, TB4, TB5, TB6, TB7, TB8, TB9) and connection points. Key connections include:
- Connect to Damper Actuator
- Connect to CMU Add-on PCB
- Connect to STC8-11 Duct Sensor OR STR1-11 Room Sensor
- Fan Speed
- Temperature Setpoint
- Status LED (LD1)
- COM, OUTPUT, POWER terminals
- Jumpers (JP1-JP11)
Remote Temperature Sensor Connection
The remote temperature sensor connection is critical for accurate temperature monitoring. The CMU is equipped with a remote temperature sensor, and users can choose between two types: the STC8-11 discharge air duct temperature sensor or the STR1-11 room air temperature sensor.
The sensor must be wired to its designated terminal block on the MAC board, even if a COM board is used. Failure to establish this connection prevents the CMU from initiating its operational cycle.
IMC10 Connection
The IMC10 connection on the MAC board provides additional control and interlocking capabilities. It uses a designated terminal block for connecting an IMC10 room control switch.
If no IMC10 is used, a jumper must be placed between pins 1 and 2 of the relevant T-block (factory default). Alternatively, these pins can be repurposed as an enable/disable contact, for example, by wiring an SIH-150 current switch to interlock the CMU with an exhaust fan. If the circuit between pins 1 and 2 opens, the CMU is disabled.
Fan Speed and Temperature Setpoint Adjustment
The MAC board features two potentiometers for control:
- P1 (Fan Speed Control): Allows adjustment of fan speed to tailor airflow.
- P2 (Temperature Setpoint): Allows users to set and fine-tune temperature setpoints for precise heating control.
Fan Speed Settings (Potentiometer P1):
- AC Fan Speed Settings: Offers a range from 0% to 100%, with specific settings indicated on a dial.
- ECM Fan Speed Settings: Offers a range from 0% to 100%, with specific settings indicated on a dial.
The minimum fan speed achievable via P1 depends on the fan type: 75% for AC fans and 15% for ECM fans.
Temperature Setpoint Settings (Potentiometer P2):
The potentiometer P2 allows setting temperatures in Celsius and Fahrenheit. A diagram shows various setpoints, such as 0°C (32°F) up to 35°C (95°F).
Note: A minimum temperature of 12°C (53.6°F) will be maintained, even if the setpoint on the potentiometer is set to a lower value.
Damper Actuator Connection
During normal operation, the MAC board closes an internal, 24VAC-rated dry contact capable of handling up to 1A of current. This terminal block can be used to drive a damper actuator or as an auxiliary switch to start other remote devices, such as an exhaust fan.
Add-On PCB Connection
The MAC board includes a dedicated terminal for integration with the CMU-COM add-on control board. This provides access to advanced control strategies through configurable Inputs and Outputs (I/Os), connection for a remote TDF user-interface module, and BACnet/Modbus communication.
Upgradeability and Standard Features
CMUs with AC fans, if initially ordered without the COM board, can be upgraded later for advanced control strategies and BACnet/Modbus integration.
The MAC board is standard on all CMUs equipped with Electronically Commutated Motor (ECM) fans.
Status LED Sequence (LD1)
The Status LED (LD1) on the MAC provides an intuitive sequence to indicate specific alarm types, aiding in troubleshooting.
| Status | LED Output |
|---|---|
| Remote Temperature Sensor Fault | Blinks 5 times and stays ON for 5 seconds. |
| Electronic Airflow Sensor Fault | Blinks 10 times and stays ON for 10 seconds. |
| Automatic/Manual Cut-out Trip | Blinks 15 times and stays ON for 15 seconds. |
| Normal Operation | Blinks once every 2 seconds. |
| Other Scenarios (e.g., ECM Fan Feedback Error, IO Configuration Error, Communication Error, No Heat Detection) | LED stays on continuously till the alarm is reset. |
Remote Monitoring and Further Information
Remote viewing and identification of triggered alarms are possible via the add-on CMU-COM circuit board, by connecting to a Neptronic TDF controller or a communication network (BACnet/Modbus).
For more information on the Compact Make-Up Air Unit, refer to the relevant CMU documents on the Documentation page.
About Neptronic
Neptronic specializes in adapting to diverse applications and has been a leader in humidification innovation since 1976, enhancing process efficiency and end-result quality by generating ideal ambient conditions.
The company is committed to research and development, aiming to continuously improve product reliability and precision. Neptronic's dedicated team of over 300 experts in Montreal, Canada, works to create ideal solutions for various applications.
