The Grässlin by Intermatic AT1 series is a compact panel-mount digital refrigeration temperature regulator designed for medium- and low-temperature commercial refrigeration applications. It integrates a high-power 16A relay for direct compressor control, two selectable sensor inputs (NTC10K or PTC1000), a fully configurable defrost management system with three distinct defrost modes, a multi-function auxiliary output, a comprehensive four-layer alarm system, condenser cleaning reminder, and RS485 communication for remote monitoring—all within a 71 × 29 mm panel cutout. This makes the AT1 a complete single-unit solution that replaces the traditional combination of a thermostat, a defrost timer, a door switch, and an alarm module.

Direct Compressor Control & Sensor Flexibility

• 16A Compressor Relay: The primary output relay is rated 16(4)A or 16(8)A at 240VAC—sufficient to directly drive the compressor of a medium-sized walk-in cooler or a reach-in display cabinet without an intermediate contactor. This reduces wiring complexity and component count inside the electrical panel.
• NTC or PTC Sensor Input: The controller supports Intermatic SN4 series NTC probes (10KΩ at 25°C) and ST1 series PTC probes (1000Ω at 25°C), selectable via the INP parameter. This lets you use whichever probe type is already installed in a replacement scenario, rather than pulling new sensor wiring.
• Two Probe Inputs: Probe T1 measures the room or cabinet air temperature for thermostat control; Probe T2 (optional, enable T2=YES) mounts on the evaporator coil and provides the temperature feedback used to terminate a defrost cycle early once the set DLI temperature is reached.
• Probe Failure Protection: If probe T1 fails, the controller enters a programmable cycling mode (CT1 minutes ON, CT2 minutes OFF) to keep the compressor running on a fixed duty cycle while the alarm E1 is displayed, protecting stored product until the probe can be replaced.

Three Defrost Modes — Configure for Your Application

• Off-Cycle Defrost (DTY=OFF): Both compressor and heater outputs are switched off. Defrost relies purely on the ambient air circulating over the evaporator. This is the default mode for coolers operating above 2°C, where ice buildup is minimal and no supplementary heat is needed.
• Electric Defrost (DTY=ELE): Compressor output turns off; the auxiliary output (when configured OAU=DEF) energises an electric heater rod embedded in the evaporator coil. Use for freezer cabinets (below -18°C) where off-cycle defrost cannot melt accumulated ice.
• Hot Gas Defrost (DTY=GAS): Both compressor and auxiliary outputs are active. A solenoid valve diverts hot discharge gas from the compressor directly into the evaporator, melting ice rapidly without supplementary electric heaters. Preferred for large walk-in freezers and blast freezers where electric defrost would add excessive heat load and energy cost.
• Defrost Parameters at a Glance: DFR sets how many defrosts occur per 24 hours (0=disabled, 1–24). DLI sets the evaporator temperature at which defrost ends early (if probe T2 is enabled). DTO sets the maximum defrost duration as a safety timeout. A manual defrost can also be triggered by holding the front-panel button for 2 seconds.

Auxiliary Output & Alarm Management

• Auxiliary Output (7(2)A): The second relay is fully configurable via the OAU parameter: set it to DEF for defrost control, LGT for cabinet light control (press a button to switch lights), ALR to close contacts when any alarm condition occurs, or 0-1 to follow the controller on/standby state for cascading multiple controllers.
• Temperature Alarms: High (AHA) and low (ALA) temperature thresholds with a configurable delay (ATD, 0–120 minutes) prevent nuisance alarms during defrost or door openings. Alarm management mode (ATM) can be set to ABS (absolute temperature thresholds) or REL (differentials relative to setpoint).
• Door Open Alarm: When a door switch is wired to the digital input (DS=YES), the controller displays "DO" and can trigger an alarm after a configurable delay (ADO, 0–30 minutes). Additionally, the compressor re-start can be delayed after the door closes (CSD, 0–30 minutes) to prevent short-cycling.
• Condenser Cleaning Reminder: The ACC parameter (0–52 weeks) tracks compressor running hours. When the accumulated time reaches the set interval, "CL" flashes on the display, prompting maintenance staff to clean the condenser coil—reducing compressor failure risk and improving energy efficiency.

Installation, Communication & Maintenance

• Standard Panel Cutout (71 × 29 mm): Compatible with the industry-standard mounting hole used by LAE, Dixell, and Eliwell controllers—the AT1 drops into most existing commercial refrigeration panel openings without metalwork.
• RS485 Communication: Built-in RS485 interface with configurable device address (ADR, 1–255) for connection to LAE supervisory software or third-party MODBUS-compatible building management systems. Operators can remotely view real-time temperatures, log alarm events, and adjust setpoints across a fleet of refrigerated cabinets from a central PC.
• IP55 Front Protection: The front face, including the membrane keypad and display window, is rated IP55—protected against dust ingress and low-pressure water jets from any direction, suitable for wiping down with cleaning solutions in commercial kitchen environments.
• Keypad Lock (LOC=YES): In self-service retail settings, the keypad can be locked to prevent customers or untrained staff from accidentally adjusting parameters. All control buttons are disabled until an authorised technician re-enters the INFO menu and sets LOC=NO.

Technical Specifications

• Power Supply: 230 V AC (E version) ±10%, 120 V AC (U version) ±10%, or 12 V AC (D version) ±10%; 50/60 Hz; 3 W
• Measurement Range: -50 °C to 120 °C (-55 °F to 240 °F); Resolution: 0.1 °C / 1 °C / °F
• Accuracy: NTC10K: < ±0.3 °C (-40 °C to 70 °C); PTC1000: < ±0.5 °C (full range)
• Operating Conditions: -10 °C to +50 °C; 15% to 80% r.H.
• Approvals: CE (EN60730-1, EN60730-2-9, EN55022 Class B, EN50082-1), UL 60730-1A

Typical Applications

• Medium-temperature reach-in coolers and upright display cabinets in supermarkets and convenience stores
• Low-temperature walk-in freezers and blast freezers in commercial kitchens and food processing facilities
• Plug-in refrigerated display cases in bakeries, delis, and butcher shops
• Heated cabinets for prepared food holding (C-H=HEA mode)
• Control panels for cold storage warehouse monitoring systems with RS485 networking