PSI D-1 Limited Warm Air, Air Conditioning & Refrigeration System ContractorPSI D 1 Limited Warm Air, Air Conditioning & Refrigeration System Contractor PSI Connecticut D 1 Limited Warm Air, Air Conditioning & Refrigeration System Contractor license allows individuals to install, repair, replace, maintain, or alter warm air, air conditioning, and refrigeration systems, including necessary piping and pumping equipment, but not oil burners. Approved References International Mechanical Code or International Mechanical Code