Reclaiming the refrigerant
When the refrigerant in a system is to be removed and the system compressor is operational it is possible to use the compressor to recover the charge. Obviously, the arrangement of the service valves on the system will affect the exact procedure.
It is possible to pump down the system in the usual manner and decant the refrigerant into a cooled recovery cylinder. It may also be possible to use the recovery cylinder installed at the compressor discharge to act as both a condenser and receiver.
In cases where the compressor has failed and the system is to be charged a recovery unit could be used to reclaim the refrigerant. There are many types of portable recovery units available which can be connected to any system service valves. A recovery unit can handle refrigerants in either liquid or vapour form. It will remove a system charge to any suitable pre-set pressure. Most recovery unit capacities range from 50 to 100 kg/h and operate on single phase 220/240 V, 50 Hz electrical supply.
It is possible to recover refrigerant from a hermetically sealed system which has no service valves by using line tap valves following the recovery unit manufacturer’s instructions.
Changing the refrigerant charge
As previously stated, exact procedures adopted by service agents may vary and the one given here is typical for replacing a refrigerant charge of CFC 12 with R134a.
The refrigerant in a system that requires replacement may be identified by the following methods:
(a) Refrigerant type stamped on the compressor nameplate.
(b) Refrigerant charge indicated on the expansion valve.
(c) By the system standing pressure.
Procedure
1 Isolate the compressor after evacuating the vapour in the compressor crankcase.
2 Drain the old mineral oil from the crankcase.
3 Replace that oil with a suitable PE oil.
4 Open compressor service valves and operate the plant.
5 Repeat step 1.
6 Drain the PE oil from the crankcase.
7 Replace with fresh PE oil.
8 Open compressor valves and operate the plant.
9 Repeat step 1 again.
10 Drain the oil and carry out a contamination check. There must be less than 1% contamination by the original mineral oil. (This test requires a special oil test kit and is easily applied.)
11 If less than 1% residual mineral oil, recover the CFC 12 refrigerant from the system.
12 Change filter drier, expansion valve and any other component necessary.
13 Evacuate the system and replace the PE oil once more.
14 Charge the system with R134a refrigerant.
Note: After step 10, if the oil contamination is still in excess of 1%, steps 1, 2, 3 and 4 must be repeated, after which another oil test must be carried out.
In reality R134a should not be charged until the oil contamination is less than 1%.
The chlorine free refrigerant R134a was selected as an example because it is available in sufficient quantities to replace R12. Another reason for its selec- tion was because there are probably a greater number of small R12 systems in the commercial field than the larger systems using other refrigerants. It can be used as an alternative for most R12 applications.