TM 9-4120-411-14
5.10 REFRIGERANT SYSTEM PRESSURE CHECK.
THIS TASK COVERS:
a. Testing
a. Testing.
(1) Install service manifold per paragraph 5.3.
(2) Check that all four service manifold valves are closed.
(3) Service manifold compound and pressure gages should indicate the same pressure. Check the reading
with the appropriate column in Table 5-1. If the system is even partially charged, the pressure should be
approximately equal to that shown in the table for the appropriate ambient temperature. If the pressure is
considerably less than shown in the table, the system does not contain enough refrigerant to continue the
pressure check. Leak check the FDECU per paragraph 5.7.
(4) Connect FDECU to power source and operate per paragraph 2.4.
(5) With the FDECU operating, allow service manifold gages to stabilize. Compare readings with those listed
in Table 5-2.
(a) If discharge and suc tion pressure are at, or near, the same value, reversing valve (L1) or compressor
(B2) failure is indicated.
(b) If discharge pressure is low and suction pressure is normal, a low refrigerant charge is indicated.
(c) If discharge pressure is normal and suction pressure is either high, or low, failure of the expansion
valve is indicated.
(d) If discharge pressure is high and suction pressure is normal, refrigerant overcharge is indicated.
(6) When pressure tests are completed, shutdown the FDECU per paragraph 2.4.
(7) Remove service manifold per paragraph 5.3.
Table 5-1. Pressure Temperature Relationship of Saturated Refrigerant R-134a.
Temperature
Pressure
2
Deg F
Deg C
psia
kg/cm
-20
-28.88
12.95
5.87
-18
-27.77
13.63
6.18
-16
-26.66
14.35
6.50
-14
-25.55
15.09
6.84
-12
-24.44
15.87
7.19
-10
-23.33
16.67
7.56
-8
-22.22
17.51
7.94
-6
-21.11
18.38
8.33
-4
-20.00
19.29
8.74
-2
-18.88
20.23
9.17
0
-17.77
21.20
9.61
2
-16.66
22.22
10.07
5-21
