Buachois Adjustable Manual Line Volt Thermostat for Heating and Cooling - Two-Way Room Mechanical Temperature Controller Switch for Central Air Conditioning

What it is and why I tried it

I picked up the Buachois mechanical thermostat to solve a simple problem: switch a line‑voltage heating/cooling circuit based on room temperature without adding electronics, apps, batteries, or schedules. Think fan-coil units, hydronic valve control, or any small line-voltage control input you want to open/close with a setpoint. It’s the kind of basic controller I like to keep on hand for retrofits, workshops, and utility spaces where “turn on around this temperature” is all that’s needed.

This is a purely mechanical, line‑voltage unit with a metal diaphragm that actuates a switch. No power is required to operate the thermostat itself, and there’s no display—just a temperature dial and a mode switch. The wiring options allow for either cutting power to a valve only (keeping a fan running) or cutting power to both, which suits common fan‑coil terminal setups.

Installation and mounting

The faceplate is a clean, square, matte white. It’s designed to mount in an 86‑type recessed box. In regions where that’s standard, installation is straightforward: two screws, tuck the wiring, and you’re done. In North America, the 86‑box footprint does not align with typical single‑gang wall boxes. I mounted it using an adapter plate to span a standard box and give a finished look; you could also surface‑mount with a shallow back box if aesthetics permit. Plan for this ahead of time to avoid a wobbly install or improvised screw locations.

Wiring is simple if you understand what you’re switching. The terminals are clearly labeled, and the included diagrams show single‑line and double‑line configurations—essentially whether you’re dropping out just the valve or the valve plus fan. Before powering anything, I always verify the contact behavior with a continuity tester: which terminal is common, which is normally open/closed, and how the mode switch routes them. That quick check saves surprises.

A practical note: the switch inside is for modest loads. If you’re switching a small valve coil or a control input on a fan controller, you’re fine. If you plan to switch a high‑current motor directly, add a relay or contactor and let the thermostat drive that instead. It’s basic good practice with compact mechanical thermostats like this.

Controls and everyday use

Operation is as straightforward as it gets:

• A temperature dial sets the target. The dial is in Celsius with the typical 10–30°C range.
• A small slide/rocker handles the mode wiring choice (your system/fan coil determines how you use it).
• No lights, no beeps, and a satisfying mechanical click as it makes/breaks.

If you prefer Fahrenheit, you’ll need to translate. I ended up penciling small reference marks near common setpoints (e.g., 20°C ≈ 68°F, 24°C ≈ 75°F). It works fine once you get used to it, but it is a consideration for mixed‑unit households or facilities.

The knob has a smooth feel with just enough resistance to avoid accidental bumps. The face is unobtrusive and looks tidy on the wall. It doesn’t scream “industrial,” which is nice for residential spaces, yet it’s clearly utility‑first.

Performance and accuracy

Mechanical thermostats live or die by two traits: differential (the swing between on and off) and scale accuracy. With the Buachois unit, I observed:

• A moderate differential around a couple of degrees Celsius. In practice, that meant the system would click on a bit below the setpoint and click off a bit above it. For a fan‑coil or hydronic valve, that’s acceptable and often desirable to reduce short‑cycling.
• The printed temperature scale is approximate. Out of the box, mine read a few degrees off from a calibrated room sensor. Once I found a comfortable setting, I left it there. If you’re expecting lab‑grade accuracy, this isn’t the tool for that. If you need “about 22°C in this area,” it delivers consistently.

Cycle behavior was stable over several weeks. The click is audible but not loud—more of a soft tick that you stop noticing after a day. There’s no hunting or chatter; just the expected single throw as the diaphragm moves.

Electrical capacity and safety notes

This thermostat is designed to switch line voltage with a compact mechanical contact. That’s ideal for:

• Water valves and small actuator loads
• Control inputs on whole‑house or attic fan controllers
• The coil of an external relay/contactor that then drives a heavier load

It’s not ideal for directly switching a large motor or heater element. If you’re unsure about your load, measure it or check the device nameplate. When in doubt, put a relay in between. It costs a few dollars and adds a lot of margin and safety. I also like to fuse the control circuit appropriately and ensure there’s adequate strain relief and conductor size inside the box.

The included wiring diagrams are helpful, but I still recommend tracing behavior with a meter before finalizing. Switch logic can look obvious on paper and still surprise you in a real panel with legacy wiring.

Where it fits best

• Fan‑coil units in small offices, workshops, or guest suites that need simple heat/cool control
• Hydronic loops where a valve needs to open/close at a comfort setpoint
• Retrofits replacing a failed mechanical stat in spaces without neutral or auxiliary power
• Any low‑power line‑voltage control input where a basic thermostat makes more sense than a smart system

Where it’s less ideal:

• Tight temperature control requirements (server rooms, process areas)
• Direct control of high‑current motors or resistive heaters without a relay
• Aesthetic‑sensitive living areas if you need a standard US wall‑box fit without adapters
• Users who prefer Fahrenheit scales and digital readouts

Build quality and longevity

The housing is basic but well‑finished. Inside, the metal diaphragm and switch feel robust for the category. Claims of high cycle counts for the contact are plausible based on the firm, clean engagement, but that’s the sort of thing you really only prove over years. After installation and burn‑in, I didn’t see any signs of arcing residue or inconsistent switching. The simplicity here is a virtue—very little to fail, no batteries to replace, and no firmware to age out.

Documentation is terse and translated, but adequate if you’re comfortable with electrical diagrams. If you’re new to line‑voltage thermostats, plan to cross‑check with a wiring guide for your specific equipment.

Pros

• Simple, reliable mechanical control with no power required
• Flexible wiring modes for common fan‑coil and valve scenarios
• Clean, unobtrusive look; easy to operate
• Consistent switching with a sensible differential for comfort systems
• Great for driving a relay or handling low‑power control inputs

Cons

• Celsius‑only scale; no Fahrenheit markings
• Scale accuracy is approximate; expect to “set by feel”
• Modest contact capacity; not suited to high‑current loads without a relay
• 86‑box mounting can be awkward in North America without an adapter
• Documentation is brief and assumes some electrical familiarity

Final recommendation

I recommend the Buachois mechanical thermostat for anyone who needs a no‑nonsense, line‑voltage control for small loads—fan‑coil valves, actuator circuits, or as a pilot for a relay. It’s inexpensive, dependable, and does exactly what a basic thermostat should do without adding complexity. You’ll want to plan for the 86‑box footprint if you’re outside regions that use it, and you should be comfortable with Celsius and with setting to comfort rather than exact numbers. If you need precise temperature control, a Fahrenheit scale, or you want to switch a heavy load directly, look elsewhere or pair this with an appropriate relay. For straightforward, low‑power applications, though, it’s a solid, practical choice that I’m happy to keep in my kit.