In my opinion, Diploma in Refrigeration and Air Conditioning is likely to fetch more job in case the candidate acquires real skill and expertise in such fields instead of merely acquiring a diploma. From jobs point of view, any degree or diploma has no value. It helps only in submitting applications where minimum eligibility criteria are specified as the degree or diploma concerned. However, during job interview, their actual knowledge is assessed by the experienced persons and a decision about offering the job or otherwise is taken accordingly. Even after getting a job, in case the candidates are not able to deliver the results, they are likely to be fired by the company.
Therefore, the author should opt for the diploma course, depending upon his aptitude and capacity/willingness to do hard work in the chosen field for becoming successful later and get a stable job.