A conversion from R12 to R134a involves a considerable risk of possible residues of decomposed refrige
rant, especially chlorine ions, or intact refrigerant and residues of mineral oil or alkylbenzenes staying in
the system. Therefore a procedure must be established during which these undesirable substances are
brought down to a level not causing substantial inconvenience in the repaired refrigeration system. Before
starting conversion to R134a it must be ensured that the original compressor motor has not ”burnt”. If this
is the case, the compressor should not be replaced since the contamination risk is too high.
Conversion to R134a always requires a compressor replacement since an original R134a compressor
must be mounted even if the R12 compressor is intact. The following procedure must be performed
continuously. If interruptions should occur, all open tubes and tube connections must be plugged. It is
assumed that the system is clean and that there is a simple evaporating circuit.
• If the system has lost its charge the leak must be traced.
• Mount a service valve on the compressor process tube.
• Collect the refrigerant which is left.
• Equalize to atmospheric pressure with dry nitrogen.
• Remove compressor and filter drier from the system.
• Flush through all system components with dry nitrogen.
• Perform the repair.
• Mount a new R134a compressor with corresponding cooling capacity.
• Mount a new filter drier with desiccant 4AXH7 or 4AXH9 or equivalent.
• Evacuate and charge the system with R134a.
For LBP systems the optimum R134a charge will be smaller than the original R12 charge. It is
recommended to start by charging 75% of the original charge and then gradually increase the charge until
the system is balanced.
• Seal the process tube.
• Check if there are leaks.
• Operate the system.
• After the repair is finished it should always be marked on the system which refrigerant and compressor
oil type it contains.
• After reassembly the system will be functional but minor oil residues from the R12 system will
circulate, which may in periods disturb injection in the evaporator, especially in capillary tube systems.
Whether this is vital for the practical use of the refrigeration system depends on the amount of oil residue.
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