OM 135
PFS 155C - 315C
13
2.
If the unit is moderately undercharged the unit will most likely trip on freeze protection. Recharge
the unit as described in the following charging procedure.
3.
If the unit is severely undercharged the unit will trip off due to lack of liquid injection. In this case
either remove the remaining charge by means of a proper reclamation system and recharge the
unit with the proper amount of refrigerant as is stamped on the unit nameplate, or add refrigerant
through the suction valve back seat port on the compressor. Feed liquid into the suction valve
when the compressor is running. If the unit is severely undercharged the unit may nuisance trip
during this charging procedure. If this happens close off the refrigerant from the tank and restart
the unit. Once the unit has enough charge so that it does not trip out continue with the charging
procedure below.
Procedure to charge a moderately undercharged PFS unit:
Note:
Refrigerant can be satisfactorily added at less than full load conditions (preferably above
50% unit load and steady state). Condensing temperature should be reasonably high and
characteristic of normal cooling tower type operation. Saturated suction temperatures should
also be at a value not higher than the design leaving chilled water temperature.
1.
Connect a refrigerant drum to the service valve on evaporator -- OR -- to the backseat port on the
suction service valve on compressor.
2.
Open refrigerant drum adding a "weighed-in" amount -- OR -- charge refrigerant during operation
of the compressor(s) until liquid line and liquid injection line sightglasses are clear.
Liquid Presence Sensor
Each compressor is equipped with a liquid sensor to assure that liquid flows to the compressor for
cooling and sealing during operation. The sensor will shutdown the compressor if liquid is not
sensed and discharge superheat increases over 5°F. At start-up the liquid sensor checks for excessive
liquid in the compressor and will delay (adjustable delay time of five minutes) start until the
compressor heater transfers the liquid out of the compressor and into the condenser. A liquid trip by
the sensor will produce an alarm message on the MicroTech display.
High Condenser Pressure Control
MicroTech is also supplied with high pressure transducers on each compressor. Although the main
purpose of the high pressure transducer is to maintain proper head pressure control, another purpose
is to convey a signal to the MicroTech control to stop the compressor in the event of an excessive rise
in discharge pressure. If the high condenser pressure control trips, the MicroTech must be manually
reset.
Mechanical High Pressure Safety Control
The high pressure safety control is a single pole pressure activated switch that opens on a pressure
rise. When the switch opens, the control relay circuit is de-energized stopping the compressors.
The control is mounted on the compressor ahead of the discharge shut off valve.
Compressor Motor Protection
The compressors are supplied with two types of motor protection.
Repeat overload trips under normal operation may indicate wiring or compressor motor problems. The
overloads are manual reset and must be reset at the overload as well as through MicroTech.
Also, the compressors have a solid-state Guardistor™ circuit which provides motor over temperature
protection. The Guardistor™ circuit has automatic reset but must also be reset through MicroTech.
