Allied Air 4HP16LT Series Installation And Maintenance Instructions Manual page 16

5. Subtract the outdoor ambient temperature from the liquid
line temperture to determine the approach temperature.
°
Liquid Line Temperature °F
°
Outdoor Ambient Temperature °F
°
Approach Temperature °F
6. Compare the approach value with those shown in Table
8. If the values do not agree with those provided in Table 8,
add refrigerant to lower the approach temperature or recover
refrigerant from the system to increase the approach
temperature.
Approach Values for TXV Systems
Approach value is the liquid line temperature minus the outdoor
ambient temperature (±1°F).
Note: For best results, use the same digital thermometer to check
both outdoor ambient and liquid temperatures.
506468-01
Table 8
Check Charge Using Normal Operating Pressures
Use Table 7 to perform maintenance checks. Table 7 is not
a procedure for charging the system. Minor variations in
these pressures may be due to differences in installations.
Significant deviations could mean that the system is not
properly charged or that a problem exists with some
component in the system.
Issue 1004 Page 16