Machine Dehydration - Carrier 17 Start Up & Operation Manual

Table 5B — HFC-134a Pressure — Temperature (C)
TEMPERATURE (C)
-18.0
-16.7
-15.6
-14.4
-13.3
-12.2
-11.1
-10.0
-8.9
-7.8
-6.7
-5.6
-4.4
-3.3
-2.2
-1.1
0.0
1.1
2.2
3.3
4.4
5.0
5.6
6.1
6.7
7.2
7.8
8.3
8.9
9.4
10.0
11.1
12.2
13.3
14.4
15.6
16.7
17.8
18.9
20.0
21.1
22.2
23.3
24.4
25.6
26.7
27.8
28.9
30.0
31.1
32.2
33.3
34.4
35.6
36.7
37.8
38.9
40.0
41.1
42.2
43.3
44.4
45.6
46.7
47.8
48.9
50.0
51.1
52.2
53.3
54.4
55.6
56.7
57.8
58.9
60.0
PRESSURE (kPa)
44.8
51.9
59.3
66.6
74.4
82.5
90.8
99.4
108.0
118.0
127.0
137.0
147.0
158.0
169.0
180.0
192.0
204.0
216.0
229.0
242.0
248.0
255.0
261.0
269.0
276.0
284.0
290.0
298.0
305.0
314.0
329.0
345.0
362.0
379.0
396.0
414.0
433.0
451.0
471.0
491.0
511.0
532.0
554.0
576.0
598.0
621.0
645.0
669.0
694.0
720.0
746.0
773.0
800.0
828.0
857.0
886.0
916.0
946.0
978.0
1010.0
1042.0
1076.0
1110.0
1145.0
1180.0
1217.0
1254.0
1292.0
1330.0
1370.0
1410.0
1451.0
1493.0
1536.0
1580.0
51
Machine Dehydration —
mended if the machine has been open for a considerable pe-
riod of time, if the machine is known to contain moisture, or
if there has been a complete loss of machine holding charge
or refrigerant pressure.
Do not start or megohm test the compressor motor or
oil pump motor, even for a rotation check, if the ma-
chine is under dehydration vacuum. Insulation break-
down and severe damage may result.
Dehydration is readily accomplished at room tempera-
tures. Use of a cold trap (Fig. 29) may substantially reduce
the time required to complete the dehydration. The higher
the room temperature, the faster dehydration takes place. At
low room temperatures, a very deep vacuum is required for
boiling off any moisture. If low ambient temperatures are
involved, contact a qualified service representative for the
dehydration techniques required.
Perform dehydration as follows:
1. Connect a high capacity vacuum pump (5 cfm
3
[.002 m /s] or larger is recommended) to the refrigerant
charging valve (Fig. 7 and 8). Tubing from the pump to
the machine should be as short and as large a diameter as
possible to provide least resistance to gas flow.
2. Use an absolute pressure manometer or a wet bulb vacuum
indicator to measure the vacuum. Open the shutoff valve
to the vacuum indicator only when taking a reading. Leave
the valve open for 3 minutes to allow the indicator vacuum
to equalize with the machine vacuum.
3. Open all isolation valves (if present), if the entire ma-
chine is to be dehydrated.
4. With the machine ambient temperature at 60 F (15.6 C)
or higher, operate the vacuum pump until the manometer
reads 29.8 in. Hg vac, ref 30 in. bar. (0.1 psia)
(–100.61 kPa) or a vacuum indicator reads 35 F (1.7 C).
Operate the pump an additional 2 hours.
Do not apply greater vacuum than 29.82 in. Hg vac
(757.4 mm Hg) or go below 33 F (.56 C) on the wet bulb
vacuum indicator. At this temperature/pressure, isolated
pockets of moisture can turn into ice. The slow rate of
evaporation (sublimination) of ice at these low temperatures/
pressures greatly increases dehydration time.
5. Valve off the vacuum pump, stop the pump, and record
the instrument reading.
6. After a 2-hour wait, take another instrument reading. If
the reading has not changed, dehydration is complete. If
the reading indicates vacuum loss, repeat Steps 4 and 5.
7. If the reading continues to change after several attempts,
perform a leak test up to the maximum 180 psig
(1241 kPa) pressure. Locate and repair the leak, and re-
peat dehydration.
Fig. 29 — Dehydration Cold Trap
Dehydration is recom-