Refrigerant Compatibility

Sometimes, and it takes three checks. First the pressure: read the class letter and the stamped rating on the nameplate against the pressures the new refrigerant will reach, including standstill. Second the charge: a flammable replacement brings a charge limit that the old exchanger volumes may break.

Third the duty. An evaporator's distribution and plate pattern were chosen for the original refrigerant, so capacity and superheat behavior can shift after conversion even when the unit is safe to keep. Send the nameplate designations and the new refrigerant and we will tell you which units carry over.

It is under-rated for the job, and it tends to get there by accident: a spare from an R134a machine has the same frame and the same connections, so it fits. S class is 31 bar at 155 C. R410A belongs in M class, up to 45 bar at 135 C.

The second difference is less visible. M is the fatigue-tested class, and a refrigerant circuit cycles pressure continuously. Check the last letter of the designation before reusing any exchanger across refrigerants. Pressure Classes sets out the full table.

On the highest pressure the refrigerant side can see and on how hard the circuit cycles. If the design pressure sits comfortably inside S, at 31 bar, and the machine runs steadily, S is a sound choice.

A machine that stages, defrosts or reverses puts repeated pressure swings through the braze joints, and M carries the fatigue qualification for exactly that. On a reversible heat pump or a short-cycling unit, choose M even where the pressure alone would allow S.

Not necessarily for operating pressure, but look at standstill before settling on less. The subcritical and cascade parts of a CO2 system run well below transcritical pressure, and there are lower tiers for them.

The trap is a stopped plant. When the compressors are off and the system warms toward ambient, pressure in the low side rises far above its running value unless something relieves or cools it. Each exchanger has to be rated for the highest pressure its section of the circuit can reach, so send the standstill strategy with the duty.

Yes, and the approval envelope is often narrower than the pressure class. ASME covers -40 C to +150 C, while CRN covers -196 C to +225 C. A low-temperature evaporator or a hot discharge-gas duty can sit inside the class and outside the stamp the job requires.

For CO2, UL approval also wants a relief valve on each side set at 0.9 times design pressure. Name the code that governs the installation at enquiry stage. Approvals and Certifications lists the envelopes.