Trane RTAA-130 Installation, Operation And Maintenance Manual Download

Page: 107 / 140

107

RTAA-IOM-3

Leaving Water Temperature Cutout

This temperature cutout provides
protection against freezing caused by
low leaving water temperature. The
setpoint is both factory set and
adjustable from Menu 4. Temperatures
below the setpoint will cause the UCM
to accelerate reduction of chiller
capacity, even to the point of
compressor shutdown. A non-latching
diagnostic will be generated if the LWT
is below the cutout for more than 30
degree F seconds.

There must be a minimum of 5 F
between the cutout temperature and
both the front panel and active chilled
water setpoints. The UCM will not
permit setting of either the front panel
or active chilled water temperatures
less than 5 F above this cutout
temperature and the display will flash
the last valid temperature.

If the leaving water temperature cutout
is set upward, the UCM will maintain
the 5 F minimum and will raise the
settings on the front panel and active
chilled water setpoints, if necessary.

Low Refrigerant Temperature
Cutout

Both circuits are protected from a
saturated evaporator refrigerant
temperature that goes below this
setting. The cutout setpoint must be a
minimum of 15 F lower than the front
panel or active chilled water setpoints.

There must be a minimum of 15 F
between the cutout temperature and
both the front panel and active chilled
water setpoints. The UCM will not
permit setting of either the front panel
or active chilled water temperatures
less than 15 F above this cutout
temperature and the display will flash
the last valid temperature.

If the leaving water temperature cutout
is set upward, the UCM will maintain
the 15 F minimum and will raise the
settings on the front panel and active
chilled water setpoints, if necessary.

If the saturated evaporator refrigerant
temperature for a circuit drops below
this setpoint for longer than 30 degree
F seconds, the circuit will be shutdown
and a CMR diagnostic will be
displayed.

Low Ambient Temperature Start

The Low Refrigerant Temperature
Cutout (LRTC) on a circuit is ignored,
briefly, each time the circuit is started.
The “ignore time” is a function of the
Saturated Condenser Refrigerant
Temperature at the time the
compressor starts, as shown in Figure
54.

Low Refrigerant Temperature
Cutout Retry

If the LTRC trips despite the low
ambient temperature start logic, the
circuit will be permitted to shutdown
and retry one time

If the LRTC trips within the first 20
minutes after initial start but after the
Low Ambient ignore time (grace
period), the compressor stops
immediately and the Restart Inhibit
timer is set to 1 minute. After time
expires, the compressor will restart if
there is a call for cooling.

If the LRTC trips again during the grace
period, a CMR diagnostic will occur. If
there is an LRTC trip anytime after the
grace period, a CMR diagnostic will
occur.

Figure 54
Low Refrigerant Temperature
Cutout Ignore Time

Low Refrigerant Temperature Cutout Time - vs - Saturated Condenser Refrigeration Temperature