Danfoss AK-PC 551 Pack Controller (080G0281) | 230V | LCD Display | 2 SSR (PWM) | Modbus | Compressor & Condenser Capacity Control

In commercial refrigeration systems, capacity control of the compressor pack (rack/pack) and common condenser is managed from a single device by the Danfoss AK-PC 551 pack controller (Danfoss code: 080G0281, ADAP-KOOL family). Based on suction pressure (Po/Pe), it drives up to 8 compressor steps and, based on condensing pressure (Pc), the condenser fans (stepped or 0-10V variable speed) with PI control. The built-in graphic LCD display and setup wizard allow fast commissioning.

Compressor and Condenser Capacity Control — Pack/Rack Controller

The AK-PC 551 manages one suction group (max. 8 relays) + one condenser group, or two suction groups (e.g. MT + LT, each max. 4 relays) + a common condenser. It is compatible with variable-speed (VLT/EC), Digital Scroll, Stream 4-cylinder, and single- and multi-step (unloader) compressors. For energy savings it offers suction pressure (Po) optimization, floating condenser control, night setback/quiet mode and load shedding.

Key Features

• Pack/rack control: 1 or 2 suction groups + common condenser; up to 8 compressors
• Built-in graphic LCD display + setup wizard (fast commissioning)
• 2× SSR (solid state relay) — PWM for Digital Scroll / Stream compressor modulation (or normal relay)
• 2× analog output 0-10V — variable speed (VLT/EC) for compressor and condenser fan
• Modbus communication — AK-SM 800 / AK-SC 355 system manager integration
• Energy savings: Po optimization, floating condenser, night mode, load shedding, heat recovery

Technical Specifications

• Brand / Model: Danfoss / AK-PC 551 (Danfoss code: 080G0281)
• Type: Electronic pack/rack controller (ADAP-KOOL); compressor + condenser control
• Supply Voltage: 110-230 V AC, 50/60 Hz
• Display: Built-in graphic LCD (optional remote display MMIGRS2)
• Inputs: 8 analog (AKS pressure transmitter + Pt1000 temperature) + 8 digital inputs
• Outputs: 6 relays + 2 SSR (PWM) + 2 analog 0-10V
• Capacity Control: 8 compressor steps; step / speed / PWM; PI control
• Communication: Modbus (RS485)
• Mounting: DIN rail, 8 DIN modules wide
• Protection Class: IP20
• Operating Temperature: -20 / +60 °C
• Power Consumption: ~10 W (230V ≈ 20 VA); weight ~0.51 kg; RTC battery CR1620
• Approvals: CE, cULus/UL, EAC, CMIM

Technician Tips

• Position the suction (Po) and condensing (Pc) pressure transmitters and the Pt1000 temperature sensors correctly; measurement errors directly affect capacity control.
• Use the 2× SSR outputs only for Digital Scroll / Stream PWM modulation; they can also be assigned as normal relays.
• Reduce energy consumption by enabling Po optimization and floating condenser control.
• Connect to the AK-SM 800 / AK-SC 355 system manager via Modbus for central monitoring and alarm management.