Carrier 07D - Manual (Page 25)

INSTALLATION
06D,07D
Before dehydrating a system make the following
preparations:
1. Obtain a pump that will produce a vacuum of
0.2 in. Hg absolute. Do not use the compres­
sor as a vacuum pump. It is not designed for
such use and may be seriously damaged.
2. Pressure test the system to be sure it is
free of leaks.
3. Obtain a vacuum indicator similar to that
shown in Fig. 20 (available from Robinair
Manufacturing Corporation, Edgerton, Ohio).
4. Keep the ambient temperature above 60 F to
speed the evaporation of moisture.
TO
COMPRESSOR TO VACUUM PUMP
SHUT-OFF VALVE
Fig. 20 - Vacuum Indicator
Description and Use of the Vacuum Indicator
The vacuum indicator consists of a wet-bulb
thermometer in an insulated glass tube con­
taining distilled water. Part of the tube is ex­
posed so the thermometer can be read and the
water level checked. When the vacuum indicator
is connected to the vacuum pump suction line,
the thermometer reads the temperature of the
water in the tube. The temperature is related
to the absolute pressure in the tube. Table 5
gives the absolute pressures corresponding to
various temperatures.
Table 5 - Vapor Pressures of Water
Temp F Observed on
Vacuum Indicator
Absolute Pressure
Inches of Mercury
70 0.739
60 0.522
55 0 436
50 0 363
45 0.300
40 0.248
35 0 204
32 0.180
NOTE:
To determine the vacuum in inches of mercury,
subtract the absolute pressure from the barometer
reading.
Handle the vacuum indicator with care. It must
be vacuum tight to give a true reading. The top
seal of the indicator is not designed to support
a long run of connecting tubes. Faster the tubes
to supports to prevent damage.
Use only distilled water in the indicator. Be
sure the wick is clean. Oil or dirt on the wick
causes erroneous readings.
To prevent loss of oil from the vacuum pump
and contamination of the indicator:
1. Install a shut-off valve in the suction line at
the vacuum pump.
2. Install a shut-off valve in the suction line at
the vacuum indicator (Fig. 20).
3. When shutting off the pump, close the indica­
tor valve and the pump valve, and turn off
the pump in that sequence.
Procedure for Dehydrating the System
1. Connect the pump and vacuum indicator to
the system. Put a "jumper" line between
the high and low side so that the pump will
draw a vacuum on all portions of the system.
Open the compressor shut-off valves. Start
the pump.
2. Open the indicator connection shut-off valve
occasionally and take a reading. Keep the
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