DERELL RES-37SD-220 | Single Output Heating/Cooling Controller with Virtual Defrost

RES-37SD-220 is a single-output digital thermostat designed for both cooling and heating control. It features a virtual defrost function without requiring an evaporator sensor, using a time-based defrost cycle on the same relay output.

It supports ON/OFF hysteresis control, compressor protection timers, and adjustable alarm limits. A digital input allows external defrost trigger, door alarm, or logic signal (e.g., mode switching).

Typical Applications: Basic refrigeration cabinets, showcase coolers, single-compressor units, cost-sensitive temperature control projects

▶︎ Technical Specifications

Power Supply: 220V AC / 50-60Hz
Relay Output: 1 x Relay (16A / 250VAC)
Sensor Input: 1 x NTC (10k Ohm, 25°C)
Control Range: -40°C ~ +150°C
Defrost Mode: Virtual (time-based, no evaporator probe)
Digital Input: Configurable for alarm, defrost, or door
Hysteresis: Adjustable via r0 parameter
Display: 4-digit 14mm LED
Front Panel Protection: IP65

▶︎ Editor’s Recommendations & Experience

This controller is ideal for projects that need cooling, heating, and basic defrosting without the cost and wiring of a second probe. The virtual defrost cycle is simple and efficient.

The output relay toggles based on both temperature thresholds and defrost time. The display shows “dEFr” during active defrost and resumes normal control afterward. Input signal flexibility adds functional value to small systems.

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