Specifications

Electrical System
Maintenance of the electrical system involves the general requirement of keeping contacts clean and connections
tight and checking on specific items as follows:
1. The compressor current draw should be checked and compared to nameplate RLA value. Normally, the
actual current will be lower, since the nameplate rating represents full load operation. Also check all pump and
fan motor amperages, and compare with nameplate ratings.
2. At least once a quarter, all equipment protection controls, except compressor overloads, should be made
to operate and their operating points checked. A control can shift its operating point as it ages, and this must be
detected so the controls can be adjusted or replaced. Pump interlocks and flow switches should be checked to be
sure they interrupt the control circuit when tripped.
Cleaning and Preserving
A common cause of service calls and equipment malfunction is dirt. This can be prevented with normal
maintenance. The system components most subject to dirt are:
1. Permanent or cleanable filters in the air handling equipment must be cleaned in accordance with the
manufacturer’s instructions; throwaway filters should be replaced. The frequency of this service will
vary with each installation.
2. Remove and clean strainers in the chilled water system and condenser water system at every inspection.
Water Treatment
Make sure tower blowdown or bleed-off is operating. Set up and use a good maintenance program to prevent
“liming up” of both tower and condenser. It should be recognized that atmospheric air contains many
contaminants that increase the need for proper water treatment. The use of untreated water can result in
corrosion, erosion, sliming, scaling or algae formation. It is recommended that the service of a reliable water
treatment company be used. McQuay International assumes no responsibility for the results of untreated or
improperly treated water.
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