Final answer:
The most likely refrigerant to be used for trailer refrigeration services is R-404A.
Step-by-step explanation:
When performing trailer refrigeration services, the most likely refrigerant to be used is R-404A. R-404A is a commonly used refrigerant in the refrigeration industry due to its high cooling capacity and low environmental impact. It is a blend of HFC (hydrofluorocarbon) refrigerants, consisting of R-125, R-143a, and R-134a. R-404A is known for its excellent thermal properties and is widely used in a variety of refrigeration applications, including trailer refrigeration.