A thermostat with the wrong fan sequence, voltage or valve output can turn a simple FCU installation into rewiring, transformer changes and repeated commissioning visits.
Compare YONGFAN electronic LCD thermostats (DA valve-only, DB valve + 3-speed fan) and mechanical dial thermostats (K206 with built-in master switch and 220 V to 24 V step-down output) across AC 180–260 V, ±1 °C accuracy, and standard 86 wall-box formats.
Specifying a valve-only thermostat (DA) where occupant control of 3-speed fan is needed leaves the fan running on fixed speed at setpoint.
Wall boxes provide 220 V mains, but valve actuators require 24 V. K206 converts voltage internally; DA/DB require matching line-voltage coils.
Thermostat outputs must match the valve drive: spring-return 2-wire vs driving open/close 3-wire synchronous motors.
All units fit standard 86 wall boxes (60 mm pitch), but mechanical fit does not guarantee electrical compatibility with existing wiring.
Opens or closes the 2-wire or 3-wire motorized water valve based on room temperature, while fan operation remains completely independent (controlled separately by schedule, local switch, or central BAS).
Combines room temperature motorized valve control with a 3-speed fan selector (High/Med/Low/Auto). When room setpoint is satisfied, both water flow and fan operation can stop together, saving energy and terminal runtime.
Rotary dial mechanical room thermostat featuring a built-in master power isolation switch and a documented 220 V input to 24 V step-down output for direct connection to 24 V motorized valves without external transformers.
| Variant | Control Type | Fan Control | Valve / Control Role | Supply Voltage | Setpoint Range | Accuracy | Key Ordering Distinction |
|---|---|---|---|---|---|---|---|
| DA (K-01) | Electronic LCD | Fan Independent | 2-wire / 3-wire motorized valve control | AC 180–260 V, 50/60 Hz | 5–35 °C | ±1 °C | Choose when thermostat controls water valve only |
| DB (K Series) | Electronic LCD | 3-Speed Fan + Auto | Motorized valve + fan synchronous control | AC 180–260 V, 50/60 Hz | 5–35 °C | ±1 °C | Choose when valve and 3-speed fan are controlled together |
| K206 | Mechanical Rotary Dial | Separate Selector (K207/8) | Room control with master switch + AC 24 V output | AC 220 V ±10% | 10–30 °C std (5–35 °C adj) | ±1 °C | Choose when mechanical control & 220 V-to-24 V conversion are needed |
Specify Valve-Only (DA) or Valve + 3-Speed Fan synchronous shutdown (DB).
Available wall voltage (220 V) and matched valve actuator voltage (220 V vs 24 V).
Confirm 2-wire spring return or 3-wire floating/directional open-close control.
Standard 86×86 mm box, 60 mm pitch, custom faceplate branding or colors.
YONGFAN controls engineers will review wiring schedules, verify valve load ratings, and confirm lead times for stock and custom OEM faceplates.
Every electronic PCB undergoes automated optical inspection to verify solder joints, component alignment, and traces.
Finished electronic thermostats are powered on test racks for continuous operational cycling before final calibration.
NTC temperature sensors are tested against precision calibrated reference probes to enforce the published ±1 °C accuracy.
High-voltage dielectric withstand tests and relay load-break tests are performed on 100% of production lots.
Choose DA (K-01) when the thermostat should close the motorized water valve while leaving fan operation independent. Choose DB (K Series) if the fan should stop with the valve.
DB (K Series) controls a 3-speed fan (High/Med/Low/Auto) together with the motorized valve. The documented K206 dial uses a separate switch (K207/K208).
Electronic DA and DB platforms operate across AC 180–260 V, 50/60 Hz. K206 uses AC 220 V ±10%.
Yes. K206 accepts 220 V input and provides a documented AC 24 V output to power 24 V motorized valve coils directly.
Identify old supply voltage, fan wire count, valve wiring (2-wire vs 3-wire), and sequence at setpoint. DA, DB, and K206 all fit standard 86 wall boxes.
Yes. Both electronic families cover a 5 to 35 °C setpoint range with ±1 °C control accuracy.
Stock DA/DB units ship in 5–10 working days; K206 in 3–7 days; OEM customized faceplates in 15–25 days after artwork approval.
No. Standard models provide standalone room control. Centralized BACnet or Modbus integration must be confirmed as a specific project option.
Room thermostats are for terminal FCU space control. AHU duct-temperature PID loops require dedicated DDC controllers.
DA (K-01) controls the valve only. Do not specify DA where the occupant expects wall-mounted fan speed selection.
K206 and DA/DB are engineered for commercial HVAC comfort. Process loops require high-precision RTD/PID instrumentation.
A thermostat cannot correct a mismatched valve. Always match thermostat output voltage and wiring to the valve actuator.
Send your FCU equipment schedule, fan speed requirements, motorized valve models, and wall voltage. YONGFAN application engineers will verify wiring compatibility, load capacity, and supply complete wiring submittals.
