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Dehydration is readily accomplished at room temperatures. Use of a cold trap (Figure 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 [.002 m
3
/s] or larger is recommended) to the
refrigerant charging valve (Figure 7 and Figure 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 machine 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 psig) (–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)