SIEMENS QAF64.6-J Frost Protection Monitor, Continuous and 2-Point (S55700-P156)

In ventilation and air conditioning plants, heat exchangers are at risk of freezing when outside air temperatures drop. The SIEMENS QAF64.6-J Frost Protection Monitor continuously measures the lowest temperature along its 6-meter capillary tube and triggers protective actions to prevent coil damage. It provides both a continuous DC 0-10 V output and a 2-point SPDT relay output, making it suitable for a wide range of control systems.

Key specifications

• Setpoint range: -10 to 15 °C
• Switching differential: 0.5 K (fixed)
• Capillary tube length: 6 m
• Operating voltage: AC 24 V
• Power consumption: 1 VA
• Protection class: IP54
• Electrical connection: Screw terminals
• Mounting type: Duct mounting (with mounting brackets)
• Housing material: Noryl (plastic)
• Ambient operating temperature: -20 to 50 °C
• Ambient storage temperature: -20 to 70 °C
• Switching capacity (relay): AC 250 V, 4 A (resistive load)
• Output current (continuous): Max. 1 mA
• Reset function: Automatic reset
• Cable entry: M16 x 1.5 (2x)

Why choose it

The QAF64.6-J offers dual output flexibility: the continuous 0-10 V signal allows precise modulation of heating or damper actuators, while the SPDT relay provides a simple on/off control for alarms or direct equipment shutdown. Its long 6-meter capillary tube covers the entire coil surface, ensuring no cold spots are missed. The automatic reset function simplifies operation after a frost event.

Ideal use cases

• Frost protection for hot water coils in air handling units
• Protection of cooling coils in mixed-air systems
• Monitoring of duct temperatures in cold climates
• Integration into building automation systems requiring analog or digital signals

Good to know

The unit is designed for duct mounting with included brackets, and the IP54 housing allows installation in dusty or damp environments. It operates on 24 V AC and consumes only 1 VA, making it energy efficient. The capillary sensor uses expansion principle for reliable mechanical temperature sensing without electronic drift.