The first prototypes were equipped with a standard Danfoss BD35F direct current compressor and an external electronic control. A big electrical capacitor (60 mF) was used in order to overcome the start torque.

During 2003 a quite new compressor BD35K became available. The new compressor is using R600a (isobutane), which does not contribute to the greenhouse effect. A new integrated electronic control was also available. This control has been developed to ensure that photovoltaric solar panels can be connected directly to the compressor without an external control and/or capacitor. The compressor is able to do a smooth start at low speed and is equipped with an adaptive energy optimiser (AEO-control). By using this control, the compressor will slowly speed up from minimum to maximum speed (from 2000 to 3500 RPM). If the panels can not give sufficient power, the compressor will stop and after a short while it will try to start again. If the start fails, the compressor will try to start again after another one minute. Once the power from the solar panels is sufficient, the compressor will start at low speed and slowly speed up again. The controller accepts a voltage between 10 and 45 Volts. The voltage from solar panels can vary, so this new feature is good for solar powered refrigerators and freezers. On a 12 V module, the compressor needs a current of about 4,5 A to start, and it can run continuously at 2 A.

Cabinets

The vaccine cooler cabinet was build by Vestfrost, and is based on a highly insulated standard cabinet. The net volume of the vaccine compartment is about 50 litres and is separated from the ice storage of about 18 kg, made by a number of standard plastic containers. The evaporator is integrated into the ice storage end during daytime forced convection is cooling the vaccine. If the temperature in the vaccine compartment gets to cold during daytime, a small electrical heating element is keeping the vaccine above freezing temperature. A thermostat controls the heater. During night time the vaccine is kept cool by natural convection from the ice department.