Trane RTHC User Manual

6 - 2 RTHC-IOM-1C
From this point, the UCP2 will be looking for a
differential to start or, basically, a requirement for
cooling.
(NOTE: differential to start is the degrees
range above setpoint that the leaving water
temperature must drift before the chiller will start.)
Until that need is apparent, no further action will
occur. The following screen will come up informing
the operator of the situation.
Assuming eventually that a differential is satisfied,
the start sequence continues, waiting only for the
restart inhibit (or other) timer to time out.
During this waiting period, the operating mode is
displayed as:
or
or
All of the above modes could occur and inhibit
starting once a demand has been established. The
first mode “Restart Inhibit” is a mode that prevents
fast cycling of the compressor motor and the build up
of heat caused by successive inrush starting currents
occurring too close together. This mode enforces an
appropriate cool-down time for the motor.
Parameters effecting this mode are dependent on
motor size and inrush characteristics and thus are
not intended to be user adjusted.
The “Staggered Start” mode provides an easy way
for a user to prevent two or more chillers in an
installation, from all starting simultaneously after a
power interruption or power application. The
Staggered Start delay setting is adjustable in the
Field Startup Group.
The last mode above is invoked if a restart is
attempted immediately following the occurrence of
certain critical “Low System Differential Pressure”
diagnostics. This mode will then prevent restart of
chiller, despite manual reset attempts, until a
predetermined cool-down time has been allowed.
The cool-down is necessary as the compressor has
been operating with less than desired oil flow rates
causing excessive rotor heating. A restart is not
allowed unless 60 minutes have expired since the
occurrence of the No System Differential Pressure or
Low System Differential Pressure Diagnostic. The
time remaining for the cool-down period is displayed
with the mode. The mode reduces the risk of serious
compressor damage that would otherwise result from
frequent starts or short cycling situations when
condenser pressures are too low.
30 seconds prior to starting, the condenser water
pump relay is energized and the UCP2 confirms
condenser water flow. Also the electronic expansion
valve is pre-positioned (40% open) and the unload
slide valve solenoid is energized. Be aware that the
start of the condenser water pump and the pre-start
unload may begin even before the restart inhibit timer
times out.
During these last few seconds before the
compressor starts, the UCP2 is completing a final
component and contactor test. Finally, the master oil
line solenoid is energized, the oil heater is de-
energized, and the compressor starter sequence
begins.
As the compressor starts, the following is displayed:
When the starting sequence is complete, unless a
diagnostic occurs, the next screen will be:
the possible limit conditions being softloading,
condenser limit, evaporator limit, current limit and
phase unbalance limit. These limits are discussed in
the following paragraphs.
Auto
Waiting For A Need To Cool
Starting is Inhibited by Restart Inhibit
Timer: Time Remaining: Min; Sec
Starting is Inhibited by Staggered Start
Time Remaining: Min; Sec
Low Diff Rfgt Pres - Overheating Cprsr
Cooldown Time Remaining Min; Sec
Starting
Unit is Running
<limit condition if applicable>

Trane RTHC Specifications

General

Brand	Trane
Model	RTHC
Category	Chiller
Language	English