Trane 120 GEH Operation Manual page 20

Microprocessor Design
The 24 volt deluxe design is a micro-
processor-based control board conve-
niently located in the control box. The
board is unique to Trane water-source
products and is designed to control the
unit as well as provide outputs for unit
status and fault detection.
The Trane microprocessor board is fac-
tory wired to a terminal strip to provide
all necessary terminals for field connec-
tions. See Figure 27 for the deluxe 24V
control board.
Deluxe 24V features include:
Random Start
The random start relay provides a time
delay start-up of the compressor when
cycling in the occupied mode. A new
start delay time between 3 and 10 sec-
onds is applied each time power is
enabled to the unit.
Anti-short Cycle Timer
The anti-short cycle timer provides a
three minute time delay between com-
pressor stop and compressor restart.
Brown-out Protection
The brown-out protection function
measures the input voltage to the con-
troller and halts the compressor opera-
tion. Once a brown-out situation has
occurred, the anti-short cycle timer will
become energized. The general fault
contact will not be affected by this con-
dition. The voltage will continue to be
monitored until the voltage increases.
The compressors will be enabled at this
time if all start-up time delays have
expired, and all safeties have been sat-
isfied.
Compressor Disable
The compressor disable relay provides
a temporary disable in compressor
operation. The signal would be provid-
ed from a water loop controller in the
system. It would disable the compres-
20
R
Features and Benefits
Deluxe Controls
sor because of low water flow, peak
limiting or if the unit goes into an unoc-
cupied state. Once the compressor has
been disabled, the anti-short cycle time
period will begin. Once the compressor
disable signal is no longer present, and
all safeties are satisfied, the control will
allow the compressor to restart.
Generic Relay
The generic relay is provided for field
use. Night setback or pump restart are
two options that may be wired to the
available relay. (Note: Night setback is
available as factory wired). An external
Class II 24VAC signal will energize the
relay coil on terminals R1 and R2.
Terminals C (common), NO (normally
open), and NC (normally closed) will be
provided for the relay contacts.
Safety Control
The deluxe microprocessor receives
separate input signals from the refriger-
ant high pressure switch, low suction
pressure switch and condensate over-
flow.
In a high pressure situation, the com-
pressor contactor is de-energized,
which suspends compressor operation.
The control will go into soft lockout
mode initializing a three minute time
delay and a random start of 3 to 10 sec-
ond time delays. Once these delays
have expired, the unit
will be allowed to run.
If a high pressure situa-
tion occurs within one
hour of the first situa-
tion, the control will be
placed into a manual
lockout mode, halting
compressor operation,
and initiating the gener-
al alarm.
In a low temperature
situation, the low pres-
sure switch will transi-
tion open after the com-
pressor starts. If the
switch is open for 45 seconds during
compressor start, the unit will go into
soft lockout mode initializing a three
minute time delay and a random start
of 3 to 10 second time delays. Once
these delays have expired, the unit will
be allowed to run. If the low pressure
situation occurs again within 30 min-
utes, and the device is open for more
than 45 seconds, the control will be
placed into a manual lockout mode,
halting compressor operation, and initi-
ating the general alarm.
In a condensate overflow situation, the
control will go into manual lockout
mode, halting compressor operation,
and initiating the general alarm.
The general alarm is initiated when the
control goes into a manual lockout
mode for either high pressure, low
pressure or condensate overflow condi-
tions.
Diagnostics
Component device connections to the
microprocessor board are referenced in
Figure 25. Three LEDs (light emitting
diodes) are provided for indicating the
operating mode of the controller. See
the unit IOM for diagnostics or trou-
bleshooting through the use of the
LEDs.
Figure 25:
Deluxe 24V
control
board.
WSHP-PRC003-EN