MS3Pro A/C Control Wiring

MS3Pro A/C Control Wiring

The MS3 ECU features a dedicated air conditioning (A/C) control option, giving you full control over how the A/C system interacts with your engine. This includes:

  • Full throttle cutout to disengage the compressor under heavy load.

  • Idle speed increase when the A/C is active for stable operation.

  • Compressor overspeed protection to prevent mechanical damage.

  • Configurable logic for safe and efficient A/C cycling.

These functions not only improve comfort but also maintain reliability and performance, especially in high-output builds.

Required Wiring

The wiring for MS3 A/C control is straightforward. You’ll need two main switches:

  1. Dash on/off switch – Allows the driver to enable or disable the A/C system.

  2. Cycling pressure switch (trinary switch) – Controls operation based on refrigerant pressure.

The trinary switch has three response conditions:

  • Low pressure cutoff – Prevents compressor operation if refrigerant has leaked out.

  • High pressure cutoff – Shuts off the compressor if refrigerant backs up between the compressor and evaporator.

  • Normal range – Allows A/C operation when refrigerant pressure is within the safe range.

Both the dash switch and pressure switch are wired inline to any available switched input on the MS3.

MS3 Input and Output Configuration

  • The A/C request input can use any available switched input pin.

  • The compressor relay output must be connected to a ground-switched output.

Example: MS3Pro Wiring

  • Digital Switched In 1 → A/C request input.

  • High Current Out 2 → Compressor relay control.

This configuration lets the MS3 fully manage compressor engagement, idle compensation, and safety protections automatically.

Why Use MS3 for A/C Control?

Integrating A/C into your standalone ECU provides:

  • Seamless load compensation (no stalling when the compressor cycles).

  • Performance-oriented safeguards (WOT cutout and overspeed protection).

  • Cleaner wiring and more flexible control logic compared to factory setups.

Whether you’re running a daily driver or a track build, MS3’s A/C control makes your system more reliable and efficient.