Specifications

CONTROLS (cont)
When the outdoor ambient temperature is above the outdoor
ambient set point and both fan coils on a compressor circuit are
calling for cooling operation, the outdoor fan runs at full speed
whenever compressor operation is permitted. When only one
fan coil is calling for cooling, fan cycling is permitted at all am-
bients. Fan motor is then cycled on and off to maintain set point
discharge pressure.
When the outdoor ambient temperature is below the specified
set point, the fan motor is cycled on and off to maintain a com-
pressor discharge pressure at the specified pressure set point.
On 538S048 units with 2 compressors running, the compressor
with the lower head pressure controls the fan operation. If only
one compressor is running, that compressor controls the fan
operation.
If the discharge pressure on either circuit exceeds 370 psig, the
outdoor-fan motor runs continuously, and the fan cycling func-
tion is bypassed until the discharge pressure decreases to
365 psig.
Units can be field configured to select head pressure control at
35 F outdoor ambient and/or 200 psig discharge pressure.
Status indicator lights — The 538S control board is equipped
with LED indicators to aid in evaluating the status of the control
system, including:
• time delay function status
• fan coil unit demand status
• head pressure control status
• current unit malfunctions
Also see System Status Red and Green LEDs and Fault Codes
table below.
Unit malfunction — Each compressor circuit is equipped with
a high-pressure switch (HPS), a low-pressure switch (LPS), and
a discharge temperature switch (DTS). These safety devices
are located in a Cycle-LOC™ device circuit that prevents com-
pressor operation if any of these safety devices is activated. The
lockout can be reset by turning the main power to the 538S unit
off, then on again.
Compressor overcurrent protection is achieved by an internal
linebreak overload, which automatically resets when the motor
temperature cools to a satisfactory level. Manual reset of Cycle-
LOC circuit may also be required.
Pressure transducers and the outdoor ambient thermistor are
monitored by the 538S controller. If a pressure transducer is
found to be out of range, the LEDs flash a code for this fault, but
the control continues to cycle the outdoor fan according to input
from the other transducer. If only one transducer is active and is
determined to be out of range, the head pressure control is by-
passed and the fan runs continuously. If the thermistor is found
to be out of range, the control allows fan cycling per transducer
input, and the LEDs flash a code for this failure. See System
Status Red and Green LEDs and Fault Codes table below for
diagnostic codes.
SYSTEM STATUS RED AND GREEN LEDs AND FAULT CODES
GREEN LED RED LED
UNIT STATUS
Number of
Flashes On
Number of
Flashes Off
Number of
Flashes On
Number of
Flashes Off
11
— Always System Ready
1 1 Low Head Pressure, Circuit 1
2 2 High Head Pressure, Circuit 1
3 3 Low Head Pressure, Circuit 2
22
1 1 High Head Pressure, Circuit 2
2 2 Low Outdoor Ambient Temperature, Outdoor Thermistor
3 3 High Outdoor Ambient Temperature, Outdoor Thermistor
33
1 1 Hardware Error
2 2 Time GuardT Device Active, Circuit 1
3 3 Time Guard Device Active, Circuit 2
LED — Light-Emitting Diode
49