D-EIMWC00804-14EN
Centrifugal Chillers
51
Repair of System
Pressure Relief Valve Replacement
Current condenser designs use two relief valves separated by a three-way shutoff valve (one
set). This three-way valve allows either relief valve to be shut off, but at no time can both be
shut off. In the event one of the relief valves are leaking in the two valve set, these procedures
must 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 leaking pressure relief valve. Remove and replace the faulty relief
valve. The three-way shutoff valve must remain either fully back seated or fully forward to
normal operation. If the relief valve farthest from the valve stem is leaking, front seat the
three-way valve and replace the relief valve as stated above.
•
The refrigerant must be pumped down into the condenser before the evaporator relief valve
can be removed.
Pumping Down
If it becomes necessary to pump the system down, extreme care must be used to avoid damage to
the evaporator from freezing. Always make sure that full water flow is maintained through the
chiller and condenser while pumping down. To pump the system down, close all liquid line
valves. With all liquid line valves closed and water flowing, start the compressor. Set the
MicroTech II control to the manual load. The vanes must be open while pumping down to avoid
a surge or other damaging condition. Pump the unit down until the MicroTech II controller cuts
out at approximately 20 psig. It is possible that the unit might experience a mild surge condition
prior to cutout. If this should occur, immediately shut off the compressor. Use a portable
condensing unit to complete the pump down, condense the refrigerant, and pump it into the
condenser or pumpout vessel using approved procedures.
A pressure regulating valve must always be used on the drum being used to build the system
pressure. Also, do not exceed the test pressure given above. When the test pressure is reached
disconnect the gas cylinder.
Pressure Testing
No pressure testing is necessary unless some damage was incurred during shipment. Damage
can be determined upon a visual inspection of the exterior piping, checking that no breakage
occurred or fittings loosened. Service gauges should show a positive pressure. If no pressure is
evident on the gauges, a leak may have occurred, discharging the entire refrigerant charge. In
this case, the unit must be leak tested to determine the location of the leak.
Leak Testing
In the case of loss of the entire refrigerant charge, the unit must be checked for leaks prior to
charging the complete system. This can be done by charging enough refrigerant into the system
to build the pressure up to approximately 10 psig (69 kPa) and adding sufficient dry nitrogen to
bring the pressure up to a maximum of 125 psig (860 kPa). Leak test with an electronic leak
detector. Halide leak detectors do not function with R-134a. Water flow through the vessels
must be maintained anytime refrigerant is added or removed from the system.
WARNING
Do not use oxygen or a mixture of R-22 and air to build up pressure
as an explosion can occur causing serious personal injury.
If any leaks are found in welded or brazed joints, or it is necessary to replace a gasket, relieve the
test pressure in the system before proceeding. Brazing is required for copper joints.
After making any necessary repair, the system must be evacuated as described in the following
section.
