TM 9-4110-254-14
5-13. REFRIGERANT SYSTEM PRESSURE CHECK.
This task covers:
Testing
INITIAL SETUP
Equipment Conditions
Testing.
(1) Check that all four service manifold valves are closed
(2) Service manifold compound and pressure gauges should indicate the same pressure Check the reading with
the appropriate column m Table 5-1 If the system is even partially charged, the pressure should be
approximately equal to that shown m the table for the appropriate ambient temperature If the pressure is
considerably less than shown m the table, the system does not contain enough refrigerant to continue the
pressure check. Leak test the refrigeration system (para 5-10).
(3) Turn the refrigeration unit on (para 4-7) and operate at desired setting.
(4) With the refrigeration unit operating, allow service manifold gauges to stabilize. Compare readings with those
(a) If discharge and suction pressure are at, or near, the same value, defrost solenoid valve (L2) or compressor
(B1) failure is indicated.
(b) If discharge pressure is low and suction pressure is normal, a low refrigerant charge is indicated If charge is
correct, refer to troubleshooting procedure (para 5-1).
(c) If discharge pressure is normal and suction pressure is either high, or low, failure of the expansion valve is
indicated If discharge pressure is high and suction pressure is normal, refrigerant overcharge is indicated.
(5) When pressure tests are completed, turn the refrigeration unit off (para 2-7) and disconnect power.
Table 5-1. Pressure Temperature Relationship of Saturated Refrigerant R-134a
Temperature
Pressure
Temperature
Pressure
Deg F
Deg C
psia
kg/cm2
Deg F
Deg C
psia
kg/cm2
-2
-18.88
20.23
9.17
-20
-28.88
12.95
5.87
0
-17.77
21.20
9.61
-18
-27.77
13.63
6.18
2
-16.66
22.22
10.07
-16
-26.66
14.35
6.50
4
-15.55
23.27
10.55
-14
-25.55
15.09
6.84
6
-14.44
24.35
11.04
-12
-24.44
15.87
7.19
8
-13.33
25.48
11.55
-10
-23.33
16.67
7.56
10
-12.22
26.65
12.08
-8
-22.22
17.51
7.94
12
-11.11
27.86
12.63
-6
-21.11
18.38
8.33
14
-10.00
29.11
13.20
-4
-20.00
19.29
8.74
5-27