The four modes differ in more than fan speed
| Mode | Who owns the fans | What sets the target | How it ends |
|---|---|---|---|
| System | macOS | Apple’s normal thermal management | It remains the default until you deliberately choose qualified control. |
| Smart Boost | macOS below the first point; Smart Breeze while engaged | An interpolated temperature-to-percentage curve, bounded by fan-reported limits and the macOS baseline | After temperature stays below first point minus hysteresis for the cooldown; Smart Breeze verifies System ownership. |
| Max | Smart Breeze for the timer | Each fan’s firmware-reported maximum | After 5, 15, or 30 minutes, or when you choose System. |
| Manual | Smart Breeze during the diagnostic session | A fixed per-fan RPM clamped to that fan’s reported bounds | When you choose System, the app exits, or a safety/failure handoff occurs. |
NoteAvailability is part of the mode definition
Smart Breeze enables Smart Boost, Max, and Manual only where it discovers a complete fan topology. Where no fans are discovered, System/monitoring is the available behavior. A curve saved in UI state cannot bypass hardware discovery.
Choose a curve for a changing workload
An automatic curve is useful when the workload repeatedly moves through warm-up, sustained work, and cool-down. The sensor becomes the input; the curve determines the requested percentage. Smart Breeze can respond earlier than macOS without holding one RPM after the thermal reason has ended, because the session has an explicit release threshold and cooldown.
- The first point decides when Smart Boost may engage.
- The slope between points decides how quickly the request rises with temperature.
- The selected sensor decides which thermal signal drives the request.
- Hysteresis and cooldown decide how convincingly the workload must cool before returning to System.
- Separate adapter and battery curves keep power context explicit.
WarningResponsive does not mean proven effective
A curve can clearly change requested airflow without changing the outcome you care about. Verify the same workload, duration, power source, thermal pressure, actual RPM, and System handoff before keeping it.
Choose fixed RPM for a narrow diagnostic question
Manual removes temperature from the target calculation. That makes it useful for a bounded question such as whether each fan approaches a substantial commanded RPM, whether left and right fan readback behave consistently, or whether a noise begins in a reproducible speed band. It is a poor default policy because it cannot adapt when the workload changes.
- Begin in System and record the fan-reported minimum/maximum plus current actual RPM.
- Set a deliberate in-range target for one short diagnostic interval.
- Compare target and actual for every fan; do not infer success from a button state.
- Return to System and verify macOS ownership immediately after the observation.
- Copy Diagnostics if actual RPM persistently fails to approach a substantial target.
WarningManual is not a hidden custom curve
Do not leave a fixed target running simply because it worked during one thermal phase. A target that seems reasonable under load can be unnecessary after the task ends and insufficient for a different task. Smart Boost encodes the temperature relationship and release path explicitly.
Choose timed Max when the question is full airflow
Max asks each discovered fan for its firmware-reported maximum for a fixed 5-, 15-, or 30-minute interval. It is the clearest way to run a short full-airflow observation without inventing absolute RPM values. The timer makes the intended end visible; it is not a substitute for diagnosis or a recommendation to run maximum cooling continuously.
| Question | Most direct starting mode | Reason |
|---|---|---|
| What does macOS do with no override? | System | It preserves Apple’s policy and gives you the control baseline. |
| Can an earlier request follow a repeating thermal load? | Smart Boost | The target responds to a named sensor and has an automatic System release. |
| Does one fan track a known stable target? | Manual | A fixed RPM isolates target/readback behavior for a bounded interval. |
| What happens during a short interval at reported full airflow? | Timed Max | It requests the reported maximum for every fan and expires automatically. |
The helper’s 95 °C protective Max is different from user-selected timed Max. The safety path samples temperature independently and remains in force regardless of the selected curve or manual target.
Compare failure behavior before convenience
The important question is not only “What RPM will I get?” but “What happens when readings disappear, the app quits, a command expires, the Mac wakes, or the helper reconnects?” Build 37 makes System the fallback for missing data and control failures. After wake, Smart Boost and an unexpired Max timer can resume after fresh checks; arbitrary Manual targets do not. After a helper or control failure, only Smart Boost may re-arm automatically. Max and Manual require deliberate user action.
- App exit and loss of the last helper connection request System.
- A missed heartbeat during manual control restores System without relying on the UI process.
- Missing temperature during manual control also causes the helper to restore System.
- Target and mode writes are read back; a failed write triggers a verified all-fan rollback request.
- After wake, arbitrary Manual targets are not silently restored.
WarningNo mode changes Apple’s final thermal authority
Smart Breeze uses a private AppleSMC interface, not an Apple-supported fan-control API. macOS and firmware remain the final thermal safety layer. None of these modes guarantees lower temperatures, performance, longevity, or protection from hardware failure.
A defensible decision in five steps
- Use System first and define the observation you cannot make under normal macOS policy.
- Confirm discovered fans and verified System ownership before enabling any control mode.
- Choose the least persistent mode that answers the question: curve for temperature response, Manual for one fixed-target check, Max for one timed full-airflow check.
- Check actual RPM and controller rather than treating the requested target as proof.
- Return to and verify System when the experiment ends; preserve diagnostics for any unexplained mismatch.
For a curve-shaped response, start with the custom-curve procedure. To select the input before the mode, read which Mac temperature sensor should control a fan curve.
Sources
- Smart Breeze safety and verified System fallback (Smart Breeze)
- Smart Breeze helper lifecycle (Smart Breeze)
- Keep your Mac laptop within acceptable operating temperatures (Apple Support)
More from the guides
Fan curvesMac fan curves: what the points actually controlLearn how a temperature-to-fan curve works on a Mac, how Smart Breeze maps each point to a bounded RPM target, and how Smart Boost returns control to macOS.
Fan curvesHow to set a custom fan curve on a MacBook ProA measured, reversible workflow for editing 2–8 temperature points, testing adapter and battery curves, and verifying actual fan response in Smart Breeze.
Fan curvesWhich Mac temperature sensor should control a fan curve?Choose Any Sensor, CPU, GPU, or Battery for a Smart Breeze fan curve by matching the sensor to a repeatable workload and checking fallback behavior.Related docs: Safety model, Helper and approval, Troubleshooting
Review the control requirements and installation checklist before trying Smart Boost, Max, or Manual. Check compatibility