Specifications

54 YORK INTERNATIONAL
the source of hot water under pressure and the cooler
head drain connection, out the cooler vent connec-
tion, into the condenser head drain and out the con-
denser vent. To avoid the possibility of causing leaks,
the temperature should be brought up slowly so that
the tubes and shell are heated evenly. Close the sys-
tem charging valve and the stop valve between the
vacuum indicator and the vacuum pump. (See Fig.
28) Then disconnect the vacuum pump leaving the
vacuum indicator in place.
6. Hold the vacuum obtained in Step 3 in the system
for 8 hours; the slightest rise in pressure indicates a
leak or the presence of moisture, or both. If, after 8
hours the wet bulb temperature in the vacuum indi-
cator has not risen above 40°F or a pressure of
6.3mm Hg, the system may be considered tight.
NOTE: Be sure the vacuum indicator is valved off
while holding the system vacuum and be
sure to open the valve between the vacuum
indicator and the system when checking the
vacuum after the 8 hour period.
7. If the vacuum does not hold for 8 hours within the
limits specified in Step 6 above, the leak must be
found and repaired.
VACUUM DEHYDRATION
To obtain a sufficiently dry system, the following instruc-
tions have been assembled to provide an effective
method for evacuating and dehydrating a system in the
field. Although there are several methods of dehydrat-
ing a system, we are recommending the following, as it
produces one of the best results, and affords a means
of obtaining accurate readings as to the extent of dehy-
dration.
The equipment required to follow this method of dehy-
dration consists of a wet bulb indicator or vacuum gauge,
a chart showing the relation between dew point tem-
perature and pressure in inches of mercury (vacuum),
(see Table 3) and a vacuum pump capable of pumping
a suitable vacuum on the system.
OPERATION
Dehydration of a refrigeration system can be obtained
by this method because the water present in the sys-
tem reacts much as a refrigerant would. By pulling down
the pressure in the system to a point where its satura-
tion temperature is considerably below that of room tem-
perature, heat will flow from the room through the walls
of the system and vaporize the water, allowing a large
percentage of it to be removed by the vacuum pump.
The length of time necessary for the dehydration of a
system is dependent on the size or volume of the sys-
tem, the capacity and efficiency of the vacuum pump,
the room temperature and the quantity of water present
in the system. By the use of the vacuum indicator as
suggested, the test tube will be evacuated to the same
pressure as the system, and the distilled water will be
maintained at the same saturation temperature as any
free water in the system, and this temperature can be
observed on the thermometer.
If the system has been pressure tested and found to be
tight prior to evacuation, then the saturation tempera-
ture recordings should follow a curve similar to the typi-
cal saturation curve shown as Fig. 29.
The temperature of the water in the test tube will drop
as the pressure decreases, until the boiling point is
reached, at which point the temperature will level off
and remain at this level until all of the water in the shell
is vaporized. When this final vaporization has taken place
the pressure and temperature will continue to drop until
eventually a temperature of 35°F or a pressure of 5mm
Hg. is reached.
When this point is reached, practically all of the air has
been evacuated from the system, but there is still a small
amount of moisture left. In order to provide a medium
for carrying this residual moisture to the vacuum pump,
nitrogen should be introduced into the system to bring it
to atmospheric pressure and the indicator temperature
will return to approximately ambient temperature. Close
off the system again, and start the second evacuation.
The relatively small amount of moisture left will be carried
out through the vacuum pump and the temperature or
pressure shown by the indicator should drop uniformly
until it reaches a temperature of 35°F or a pressure of
5mm Hg.
When the vacuum indicator registers this temperature
or pressure it is a positive sign that the system is evacu-
ated and dehydrated to the recommended limit. If this
level can not be reached, it is evident that there is a leak
somewhere in the system. Any leaks must be corrected
before the indicator can be pulled down to 35°F or 5mm
Hg. in the primary evacuation. During the primary pull-
FIG. 29 - SATURATION CURVE
LD00474