Bard Advanced Solid State Dual Unit Lead/Lag Controller with Alarm Board MC4002-A

The Bard MC4002-A Advanced Solid State Dual Unit Lead/Lag Controller is designed to manage and sequence two HVAC systems, ensuring balanced runtime and reliable temperature control in mission-critical environments such as telecom shelters, equipment rooms, data facilities, and commercial installations.

The MC4002-A provides four stages of cooling control and up to four stages of heating when configured for heat pumps, allowing proper operation with economizers, two-stage compressors, or dual compressor systems. By automatically rotating which unit serves as the lead system, the controller balances equipment wear while maintaining precise temperature control.

A digital LCD display provides building temperature readout and easy configuration of operating parameters. LED indicators show active cooling or heating stages along with which unit is currently operating as the lead unit.

Unlike the base MC4002 model, the MC4002-A includes an integrated alarm relay board, providing expanded monitoring capabilities for HVAC system status and environmental conditions. These alarms can be connected to building management systems or external monitoring equipment using Form C dry contact relay outputs (NO/NC).

Alarm Monitoring Capabilities

The integrated alarm board provides monitoring and relay outputs for:

• Power loss alarm relay for both units

• High pressure / low pressure refrigerant lockout alarm relay

• Smoke or fire shutdown alarm relay

• Low temperature alarm thermostat and relay

• High temperature alarm thermostat and relay

LED indicators on the controller front panel display active alarm conditions for quick diagnostics.

Key Features

• Controls two HVAC units in automatic lead/lag rotation

• 4 stages of cooling control

• Up to 4 stages of heating when configured for heat pumps

• Compatible with systems with or without economizers

• Designed for 2-stage or dual compressor systems

• Integrated alarm relay board

• Form C dry contact alarm relays (NO/NC) for external monitoring

• Digital LCD display for temperature monitoring and programming

• LED indicators for active stages, alarms, and lead unit status

• Local temperature sensor included

• Supports two optional remote sensors

• Humidity control capability

• Generator run input to prevent A/C operation during generator testing

• Smoke/fire shutdown circuit

• Anti-short cycle compressor protection

• Durable 20-gauge metal enclosure

MC4002 Series Comparison

The MC4002-A sits in the middle of the MC4002 controller lineup:

The MC4002-A is ideal for installations that require lead/lag HVAC control with integrated alarm monitoring, but do not require network connectivity.