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Isotherm 3251SP 125L ASU Fridge Kit - Sea Water Cooled - 2023 Model - Allow 6 Weeks from Order

Make use of that Coolbox or build your own. Then enjoy all the benefits of a Fridge/Freezer much the same as home. Purchase a mains rectifier and run it off the Mains when you are in Marina's. If in doubt give us a call, we are here to help

Even on the hottest day the water-cooled Isotherm SP operates consistently at an extremely high level of efficiency. Without fans or pumps to remove the heat generated by the compressor, the SP system consumes much less battery power and is remarkably quiet.

ASU vs Classic Refrigerator
Isotherm ASU charges the holding plate while the engine is running.
The patented ASU system has now been available for more than 15 years and has been installed on tens of thousands of boats worldwide. The ASU system always starts the compressor when the engine is running and the power is "free" to chill the holding plate completely. The energy stored in the holding plate will keep the refrigerator cool for many hours. When the engine is stopped, the compressor will not restart until the energy stored in the plate is all but consumed. Only then will the compressor start to run for short periods to maintain the required temperature in the box. The ASU system always uses the stored energy first before automatically starting the compressor when the engine is running. With its unique principle of operation - the patented ASU "Automatic Start Up" system - Isotherm ASU has the advantage over traditional refrigerators.

ASU - Automatic Start Up
This unique system is designed to run the compressor primarily when the engine is running and plenty of power is available, making it preferable to have as large a compressor as possible to chill the holding plate rapidly. By taking advantage of the surplus energy generated by the alternator when the engine is running, the ASU feature does not reduce the engine's effectiveness. The Isotherm ASU system increases the speed of the compressor up to 75% when the engine is running to freeze the holding plate rapidly and effectively. This can only be done by a three-phase compressor with full-range speed control. The "intelligent" microprocessor is useful even when running only off the battery. If, for example, a crate of warm beer is placed in the refrigerator, or its door is inadvertently left open, the ASU function will speed up the compressor just enough to keep its contents cool. For larger refrigeration requirements and greater energy sources, Isotherm TWIN ASU is a good option. The Isotherm Twin system expands the refrigeration range from one compressor running at low speed to two compressors running at high speed. With both brain and brawn, Isotherm automation turns on full power only when it's required - and available!

Using air which is blown through the condenser by a fan is the traditional way to remove the heat. It is important that the compressor compartment is well ventilated allowing cold air to enter from below and hot air to escape to the top.

Key Features

  • Fridge or Freezer use
  • 12/24 V Danfoss / Secop compressor
  • Universal kit AC/DC optional for a complete power supply compatibility (12/24 V, 230/115 V and 50/60 Hz)
  • SP system (patented) to avoid the noise of a ventilated condenser and reach a very low power consumption
  • The perfect combination for sailing yachts


  • Compressor: BD35F
  • Dimensions Compressor H x W x D (mm): 280 x 175 x 160
  • Dimensions Holding Plate H x W x D (mm): 300 x 210 x 60
  • Max. Box Volume Fridge (l): 125
  • Max. Box Volume Freezer (l): 40

PS Please allow 6 weeks for delivery

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