Nov 2004: Converting R22 Systems to R407C

10th November 2004

The following is a set of general guidelines to assist in the replacement of R22 condensing units with equivalent R407C units. They are not meant to replace any existing relevant standards or recommended good practice.

All work must be carried out by appropriately qualified refrigeration and/or electrical personnel, complying with local and national codes of practice.

  1. Condensing units built and supplied by IMI Air Conditioning Ltd, (now Marstair Ltd), before 1999, for use with R22 will contain mineral oil. R407C units will contain polyolester oil (POE). Check the compressor label to confirm the type of oil in the system. For safe system operation, it is essential to remove the mineral oil from the existing system, as R407C is not compatible with mineral oil.  On completion of the change over the concentration of mineral oil remaining in the system should not exceed 5% of the total oil charge.
  2. In order to recover as much oil as possible to the condensing unit, the system should be pumped down prior to disconnecting the condensing unit.
    a. With the power turned off, disconnect the low-pressure switch (if fitted) from the unit control circuit.
    b. Fully shut off the liquid line valve (upstream of the expansion device) on the side of the condensing unit or heat pump outdoor unit.
    c. Connect service gauges to monitor the suction pressure.
    d. Switch the system on and run in cooling. Ensure the compressor is running.
    e. Monitor the suction pressure and when it drops to 2psig fully shut off the suction valve on the side of the unit and switch the unit off.
  3. Using the appropriate recovery system and bottle, recover the remaining refrigerant in the indoor unit and interconnecting pipework.
  4. Ensure the mains power to the condensing unit is safely isolated.
  5. Disconnect the electricity supply and interconnecting pipework at the condensing unit (including the expansion device) and remove the unit.
  6. Seal the ends of the interconnecting pipework immediately to prevent unnecessary exposure to moisture or dirt ingress.
    Note:  The condensing unit will still contain a charge of R22 refrigerant, which must be safely reclaimed prior to the unit being disposed of.
  7. Using a suitable proprietary flushing agent, like Endoflush (available from Heronhill), thoroughly flush the interconnecting pipework and indoor unit in order to remove remaining traces of mineral oil. 
  8. Blow the pipework through with Oxygen Free Nitrogen to remove any residue left by the flushing agent.
  9. Install and connect the new condensing unit.  Do not open the suction and liquid line valves.
  10. If the system is fitted with a filter/drier this should be changed for one suitable for use with R407C.
  11. Pressure test the interconnecting pipework joints.
  12. The interconnecting pipework and indoor unit should be evacuated using a triple evacuation procedure.
  13. When satisfied that the pipework connections are sound, break the vacuum by opening the suction and liquid line valves.
  14. First check the wiring diagram on the new condensing unit, as the connections may be different to those on the original unit. Reconnect the electricity supply,
  15. Re-commission the system following the instructions provided with the units.
  16. It is advisable to test the oil, with a proprietary oil test kit, after about 100 hours of operation to confirm that the concentration is within the 5%/95% tolerance.