Rusty Macs Fan Control

A Rust reimplementation of Macs Fan Control for Windows on Apple hardware (Boot Camp). It monitors fan speeds and temperature sensors and lets you set each fan to a constant speed or have it follow a temperature sensor.

It is a single native executable of about 1.3 MB with no Qt runtime. The behaviour was worked out by reverse engineering version 1.5.21 of the original and reimplementing it; no code from the original is included.

Use at your own risk. This program overrides your Mac's own fan control. Setting fans too low can let the machine overheat. The original app's warning applies here too: it is for advanced users who know how to use it without harming their Mac.

This project is not affiliated with or endorsed by CrystalIDEA. "Macs Fan Control" is their product.

Requirements

• An Intel Mac running Windows 10 or 11 (64-bit) through Boot Camp.
• The original Macs Fan Control installed. This app does not ship a kernel driver; it uses the signed applesmc.sys driver that the original's installer registers as the AppleSMC service. Language files are also read from the original's install folder.
• Administrator rights. Starting the driver needs them, so Windows asks for elevation each time the app starts.

Do not run this app and the original at the same time. They share settings and would both try to control the fans.

Install

Download the zip from the Releases page, unpack it anywhere and run RustyMacsFanControl.exe.

The executable is not code signed, so the elevation prompt shows an unknown publisher and SmartScreen may warn the first time.

Using it

• Main window. Fans are on the left with their minimum, current and maximum RPM. Temperature sensors are on the right.
• Auto / Custom... Each fan has two buttons. Auto hands the fan back to the system. Custom... opens a dialog where you choose a constant RPM or a sensor-based value with a start temperature and a maximum temperature.
• Presets. Automatic and Full blast are built in. After changing a fan the preset shows as Custom*; save it under a name from the button next to the preset name.
• Tray icon. Closing or minimizing the window keeps the app running in the notification area. Double-click the icon to bring the window back, right-click for the menu. Exit in that menu quits the app and returns every fan to automatic control.
• Preferences. Autostart at logon, language, Fahrenheit, one-decimal temperatures, and a sensor whose temperature is drawn in the tray icon.

The active preset is remembered. If you quit with a fan on a custom setting, that setting is applied again the next time the app starts.

Command line

Switch	Effect
/minimized	Start hidden in the notification area (used by autostart).
/log	Write the log next to the executable instead of %TEMP%\RustyMacsFanControl.log.
/applesmc	Use the applesmc.sys driver even on Macs where Boot Camp's driver would be tried first.
/skipcheck	Skip the Apple-hardware and virtual-machine checks.
--probe	Print the fans and temperatures the SMC reports, then exit. Read-only.

What is missing compared with the original

• Temperatures of disk drives (NVMe/SATA) and of NVIDIA/AMD graphics cards read through their own drivers. Only sensors reported by the SMC are shown.
• The "Create tech zip file" command and the /smcdump switch.
• Dark mode.
• The direct port I/O fallback (inpout32.dll) used on very old Macs. It is a 32-bit DLL and this is a 64-bit program.
• Licensing, the trial, the update checker and the upgrade dialogs are intentionally left out. Custom presets are always available.

Settings are stored in the same registry key as the original (HKCU\Software\CrystalIdea Software\Macs Fan Control), so presets carry over in both directions. Autostart uses its own task named RustyMacsFanControl.

Building

You need Rust (MSVC toolchain), the Windows SDK and Python 3.

The icons, sensor name tables and English strings belong to CrystalIDEA and are not stored in this repository. Extract them from your own installed copy first:

python -I re/scripts/extract_assets.py "C:\Program Files (x86)\Macs Fan Control" app/assets
cargo test --manifest-path app/Cargo.toml
cargo build --release --manifest-path app/Cargo.toml

The result is app/target/release/rusty-macs-fan-control.exe.

Debug builds do not request elevation, so they can only reach the SMC when started from an elevated terminal. --demo runs a debug build against a simulated SMC instead, which is enough for working on the interface.

Releases

Pushing a tag such as v0.2.0 runs .github/workflows/release.yml. It checks that the tag matches the version in app/Cargo.toml, downloads a zip of the app/assets folder from the address stored in the ASSETS_URL repository secret, runs the tests, builds the release executable and attaches it to a GitHub release. The workflow pins the zip's SHA-256, so update that value in the workflow whenever the zip changes.

Repository layout

Path	Contents
app/	The Rust application.
re/spec/	Behavioural notes on the original that the implementation follows: SMC access, fan control, sensors and user interface.
re/scripts/	Tools used for the analysis: Ghidra dump scripts and the resource extractors.