mpo55Danfoss MP 55 Differential Pressure Switch is used in refrerating systems with R717 and also systems with HCFC and non-flammable HFC refrerants. MP 55 Pressure Switch has a fixedMelting Point System MP55 Simple and Versatile. The MP55 is the ideal starter model and offers simultaneous determination of up to 3 melting pointmelting range or 2 slip melting point