Assuming the restriction in the drier is only partial, and that a low pressure cut-out control is in circuit, the following procedure should be adopted:
1. Note the pressure at which the compressor cuts out. The control must be reset to the original setting after the filter drier is replaced.
2. Alter the range of the low pressure control and pump down the system as previously described. Ensure that the suction service valve is front seated when this is completed.
3. Isolate the plant electrically.
4. Remove the defective filter drier and replace it. Take care that the new one is installed correctly; note the direction of flow.
5. Open the liquid shut-off valve at the receiver.
6. Leak test the joints which have been disturbed.
7. Loosen the connection on the suction line at the inlet to the compressor and allow a small amount of vapour to escape, tighten connection.
8. Set the suction service valve to the operating position and operate the plant.
9. Reset the low pressure control to its original cut-out setting.
10. Remove gauges, fit service valve caps and carry out a final leak test.
11. Clear the site of debris etc.
Should the filter drier be completely blocked, which is improbable, then the replacement procedure will be the same as that given earlier for the replacement of a thermostatic expansion valve with a complete loss of charge.
