Parameter Generation and Control 9354-4250 Installation And Operation Manual Download

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PGC, Inc

500-1000 CFM Air Handler

May 2006

Appendix A

A-9

AFETY

EVICES

The unit is equipped with several safety devices to guard against serious trouble due to failure of
any components.

Alarm contacts are available on the PLC, which will switch when either of the process variables
is in an alarm condition. The process variables are Air and Water in Two-Temperature mode, or
Air and Rh in any other mode. The alarm type, set points, and time delay are all programmable
from the SmartPad™; and the alarm can be disabled from the SmartPad™; refer to the
SmartPad™ manual for further information. The alarm contact is a single-pole double-throw
(SPDT), Normally Open / Normally Closed, dry contact relay rated at 6 Amps @ 250VAC.

Compressor Internal Overload:

The refrigeration compressor is equipped with an internal

thermal protector. If the compressor draws excessive current, the motor windings will overheat. If
the windings overheat, the internal thermal protector will open and the compressor will not
operate. The rest of the chamber will continue to function, although it is not possible to control air
or water temperature unless the compressor is operating. As soon as the internal temperature of
the compressor motor drops to a safe operating level, the compressor will resume operation. This
reset process will normally require about 45 minutes.

Several potential causes of a compressor internal overload include the loss of coolant water flow,
excessive coolant water temperature, clogged coolant water inlet filter, high ambient temperature,
or excessive refrigerant charge, low line voltage, or unusually high ambient temperature.

Refrigeration High Pressure Fault:

A pressure switch monitors the discharge pressure in the

refrigeration system. This switch is located beside the compressor. If the pressure is allowed to
operate at an excessive level, the compressor will be damaged. If the high-pressure switch opens,
the SmartPad™ will pad indicate “HIGH PRESSURE FAULT SET” and the system will shut
down. The high-pressure switch will automatically reset after the refrigeration discharge pressure
falls below the pressure trip point. When the switch is reset, the SmartPad™ display will indicate
“HIGH PRESSURE FAULT CLEAR”, and the system may be restarted by pressing the Standby
key on the SmartPad™ key

Several potential causes of a compressor internal overload include obstructed or dirty air cooled
condenser, excessive refrigerant charge, low line voltage, or unusually high ambient temperature.

Refrigeration Low Pressure Fault

A pressure switch monitors the suction pressure in the

refrigeration system. If this pressure is allowed to operate below a safe level, the compressor may
be damaged. If the low-pressure switch opens, the SmartPad™ will indicate “LOW PRESSURE
FAULT SET” and the system will shut down. The low-pressure fault will automatically reset
when the refrigeration suction pressure rises above the pressure trip point; when this occurs, the
SmartPad™ display will indicate “LOW PRESSURE FAULT CLEAR”, and the system may be
restarted by pressing the Standby key on the SmartPad™ key pad.

Some potential causes of a low-pressure fault include, but are not limited to, low refrigerant
charge, frozen evaporator, or a poor spray pattern.