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Section 3 • Installation
CO2 Systems
A CO2 system will tend to be more prone to leaks due to
the higher working pressures and the smaller molecule
size, and therefore its leak detection should become a
regular maintenance procedure. For a charge size of
above 661 lbs, for example, the recommendation would
be to perform the leak detection procedure about 4
times a year.
An oil stain will be a visual indicator of a CO2 leak, but
there are also leak detection sprays available in the mar-
ket (such as Weicon´s or Bulleye´s), infrared hand held
leak detectors (such as D-TEK CO2), and ultrasonic leak
detectors of several brands
Evacuating The System
A refrigeration system operates best when only refrig-
erant is present. Steps must be taken to remove all air,
water, vapor, and all other non-condensables from the
system before charging it with refrigerant. A combina-
tion of moisture and refrigerant, along with any oxygen
in the system, can form acids or other corrosive com-
pounds that corrode internal parts of the system.
To properly evacuate the system, and to remove all non-
condensables, air and water vapor, use a high vacuum
pump capable of attaining a blanked off pressure of 50
microns or less. Attach this pump to the system and al-
low it to operate until system pressure is reduced some-
where below 1000 microns. Evacuation should not be
done unless the room temperature is 60°F or higher.
Attach vacuum gauge(s), reading in the 20 to 20,000
micron gauge range, to the refrigerant system. These
gauge(s) should be used in conjunction with the high
vacuum pump. The reading from the gauge(s) indicates
when the system has reached the low absolute pressure
required for complete system evacuation.
Connect the high vacuum pump into the refrigera-
tion system by using the manufacturer's instructions.
Connect the pump both to the high side and low side
of the system, to insure system evacuation. Attach the
vacuum gauge to the system in accordance with the
manufacturer's instructions.
A single evacuation of the system does not satisfac-
torily remove all of the non-condensable, air and wa-
ter vapor. To do a complete job, a triple evacuation is
recommended.
2
Information taken from Commercial CO2
Refrigeration Systems Guide for Subcritical and
Transcritical CO2 Applications, by Emerson.
VSS/VSM/VSH/VSSH • Installation, Operation and Maintenance Manual • Emerson • 35391SD
.
2
When the pump is first turned on, bring system pressure
to as low a vacuum level as possible, and continue opera-
tion for 5 to 6 hours.
Stop the pump and isolate the system. Allow the unit to
stand at this vacuum for another 5 to 6 hours. After this
time, break, the vacuum and bring the system pressure
up to 0 psig with dry nitrogen.
To begin the second evacuation, allow the pump to op-
erate and reduce the pressure again to within 50 to 1000
microns. After this reading is reached, allow the pump
to operate 2 or 3 hours. Stop the pump and let the sys-
tem stand with this vacuum. Again using dry nitrogen,
raise the system pressure to zero.
For the third evacuation, follow the previous procedure
with the pump operating until system pressure is re-
duced below the 1000 micron level. Run the pump an
additional 6 hours and hold the system for approximate-
ly 12 hours at low pressure. After this, again break the
vacuum with dry nitrogen and allow the pressure in the
system to rise slightly above zero pounds (psig). Install
new drier cartridges and moisture indicators. Charge
the system once more below the 1000 micron level and
use the refrigerant designed for the system.
When properly evacuating the system as outlined
above, the system is dry, oxygen-free and free of non-
condensables. The piping should not be insulated be-
fore the evacuation process is started. If moisture is in
the system before evacuating, it condenses in low places
and freezes. If this happens, it can be removed by gently
heating the trap farthest away from the vacuum pump.
This causes the ice to melt and water to boil. Water va-
por collects in the next trap towards the vacuum pump.
This process should be repeated until all pockets of wa-
ter have been boiled off, and the vacuum pump has had
a chance to remove all the water vapor from the system.
3 – 19
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Troubleshooting
