TM 9-4110-256-14
5-14.
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 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 test the refrigeration
(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
(a)
If discharge and suction pressure are at, or near, the same value, defrost solenoid valve (L2) or
(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.
(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
kg/cm2
kg/cm2
Deg F
Deg C
psia
Deg F
Deg C
psia
-20
-28.88
12.95
5.87
-2
-18.88
20.23
9.17
-18
-27.77
13.63
6.18
0
-17.77
21.20
9.61
-16
-26.66
14.35
6.50
2
-16.66
22.22
10.07
-14
-25.55
15.09
6.84
4
-15.55
23.27
10.55
-12
-24.44
15.87
7.19
6
-14.44
24.35
11.04
-10
-23.33
16.67
7.56
8
-13.33
25.48
11.55
-8
-22.22
17.51
7.94
10
-12.22
26.65
12.08
-6
-21.11
18.38
8.33
12
-11.11
27.86
12.63
-4
-20.00
19.29
8.74
14
-10.00
29.11
13.20
5-29