106
Chapter 5
D. Charge the System and Check the
Pressure Drop
Charge the system and place in operation. Follow
the safety precautions outlined in “System Charg-
ing” on pages 5-6. Immediately after startup, check
the pressure drop across the suction line filter-drier.
This will serve two purposes:
•
Verify that the drier selection was correct; that
is, large enough.
•
Serve as a base point to which subsequent pres-
sure checks can be compared.
Because the permissible pressure drop across the
drier is relatively small, it is suggested that a differ-
ential pressure gauge be used for the measurement.
E. Measure the Pressure Drop
After the system has been operating for an hour or
so, measure the pressure drop across the suction line
filter-drier.
In the case of Compressor Housing Contamination,
little change should be noted. The pressure drop
will, in most instances, be below that tolerable for a
permanent installation (see Table 5-3).
On the other hand, where System Contamination
occurred, an increased pressure drop will be mea-
sured. Change the suction filter-drier and the liquid
line filter-drier whenever the pressure drop
approaches or exceeds that allowed for temporary
operation during cleanup (see Table 5-4).
Keep changing both the suction and liquid line fil-
ter-driers until the pressure drop stabilizes at a figure
equal to or below that permitted for permanent
operation in a system (see Table 5-3). At this point,
it is the service person’s option as to whether to leave
the suction drier in the system or remove it from
operation.
If the system is to be opened to permit the perma-
nent removal of the suction filter-drier then the liq-
uid line filter-drier should be changed once more.
Table 5-3: Suggested Maximum Pressure Drop (PSI) for Permanent Suction Filter-Drier Installation
Application
Air Cond.
High
Medium
Low
Low
Evaporator Range, °F
+55 to +32
+55 to +20
+30 to -10
+10 to -20
-20 to -40
R-12
2
2
1 1/2
1/2
1/2
R-22
3
3
2
1
1/2
R-502
3
3
2
1
1/2
Table 5-4: Suggested Maximum Pressure Drop (PSI) for Temporary Suction Filter-Drier Installation
During Cleanup
Application
Air Cond.
High
Medium
Low
Low
Evaporator Range, °F
+55 to +32
+55 to +20
+30 to -10
+10 to -20
-20 to -40
R-12
9
9
6
2
3/4
R-22
15
15
9
3
1 1/2
R-502
15
15
9
3
1 1/2
