Piper conversion of air conditioning systems from using R12 to R134a refrigerant on aircraft models listed. For PA-31-300 s/n 31-660, 31-712 thru 31-900, 31-7300901& up. For PA-31-325 sns 31-7400990 & up. PA-31-350 sns, 31-5001& 31-5003, 31-7305005 up View PDF on drs.faa.gov ↗

The STC PDF is authoritative: installation instructions, ICA requirements and limitations.