The triple evacuation method is recommended and is par-
ticularly helpful if the vacuum pump is unable to obtain the
desired 1 millimeter of vacuum. The system is first evacuated
to approximately 29 inches of mercury. Enough refrigerant
vapor is then added to the system to bring the pressure up
to zero gauge pressure. Then the system is once again
evacuated to approximately 29 inches of mercury. This is
repeated 3 times. The second pull down will remove about
90% of that remaining from the first pull down and after the
third, only
1/10
of 1% non-condensables will remain.
REFRIGERANT CHARGING
The
McQuay
centrifugal chillers normally use R-12, or R-500
refrigerant; therefore, it is recommended that the operator
check the unit nameplate to assure the correct refrigerant
selection prior to charging or adding refrigerant.
An initial operating charge is made at the factory prior to
shipment. In the event the operator needs to add refrigerant
after the unit is installed, certain precautions should be taken
to protect equipment components. Refrigerant charging lines
must be kept dry, clean and free of non-condensable gases.
Care should be taken in selecting the best charging point in
the unit so as to protect the equipment from damage.
If the entire charge is lost or removed from the unit, recharg-
ing can be accomplished quickly and safely by introducing
the liquid refrigerant directly into the bottom of the evaporator
with the expansion valve manually opened. Both condenser
water and chilled water must be flowing through the respec-
tive vessels to prevent localized freezing. Consult the chiller
nameplate for the proper refrigerant charge.
With a near-normal charge in the system, final charging
can best be accomplished with the unit running with the com-
pressor at full load. In this operating mode the unit should
be charged until suction superheat is between
2”
and
6”F,
adjusting the thermal expansion valve as necessary. Con-
tinue charging until
9” to 11
OF
liquid subcooling is obtained
leaving the condenser if the unit is operating at full load. At
less than full load, liquid subcooling will be proportionally less.
PRESSURE RELIEF VALVE REPLACEMENT
Current condenser designs use two relief valves (1 set)
separated by a three-way shutoff valve. In the event one of
the relief valves is leaking on the two valve set, the following
procedures should be followed:
If the valve closest to the valve stem is leaking, back seat
the three-way valve all the way, closing the port to the leak-
ing pressure relief valve. Remove and replace the faulty relief
valve. The three-way shutoff valve should remain either fully
back seated or fully forward for normal operation. If the relief
valve furthest from the valve stem is leaking, front seat the
three-way valve and replace the relief valve and replace the
relief valve as stated above.
EQUIPMENT WARRANTY
Each PEH/PHH centrifugal chiller manufactured by McQuay
startup or 18 months from date shipped by the company,
carries a standard limited warranty. This warranty covers
whichever comes first.
repair or replacement of component parts which prove
defec-
For a complete description of this warranty refer to the
war-
tive in material or workmanship within 12 months from initial
ranty form furnished with the equipment.
REFRIGERANT CHARTS
FIGURE 12.
IM 307 I Page
17
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