Limit Conditions; Seasonal Unit Start-Up Procedure - Trane RTHC Installation Operation & Maintenance

After the starting sequence ends, the UCP2 checks
for a complete starter transition, begins a run unload
mode, and energizes the unload solenoid for 30
seconds
In the normal mode, the compressor slide valve will
modulate to satisfy the leaving water setpoint. Also
the EXV will modulate to maintain the desired liquid
level control in the evaporator.

Limit Conditions

The UCP2 will automatically limit certain operating
parameters during startup and run modes to maintain
optimum chiller performance and prevent nuisance
diagnostic trips. These limit conditions will be noted
as a second line of the operating mode display "Unit
is Running." (See Table 16 in section 5 for the
possibilities.) First the limit condition is noted as, for
example
Unit is Running
Capacity Limited By Low Evap Temp
As the adaptive controls initiate machine actions, the
status of those actions will appear as the second line
as, for example
Unit is Running
Establishing Minimum Capacity Limit
The following are limit controls, all of which the UCM
will limit to adjustable setpoints:
q Current Limit Control - The UCM reads the
current from the current input and limits it using
the solenoid valves that operate the slide valve.
q Condenser Limit Control - The UCM converts
the saturated condensing refrigerant sensor
reading to a pressure and limits it using the
solenoid valves that operate the slide valve.
q Evaporator Limit Control - The UCM reads
evaporator refrigerant temperature from a
temperature sensor and limits it using the
solenoid valves that operate the slide valve.
q EXV/Liquid Level Control - The UCM reads the
evaporator liquid level sensor output and
maintains it by opening and closing the EXV.
q Soft Loading - Soft loading prevents the chiller
from going to full capacity during the cooldown
Installation, Operation and Maintenance
period (often done by imposing a current limit) or
slows the rate of loading during the initial pull-
down (by limiting the loading).
q Minimum Capacity Limit - This control operates
in direct response to the compressor discharge
temperature and will force load the compressor in
an attempt to head off a high discharge
temperature cutout and diagnostic.
Note: While limit controls are in effect, sudden
variations in some display readings and machine
actions will be observed.

Seasonal Unit Start-Up Procedure

1 Close all valves and re-install the drain plugs in
the evaporator and condenser headers.
2 Service the auxiliary equipment according to the
start-up/maintenance instructions provided by the
respective equipment manufacturers.
3 Vent and fill the cooling tower, if used, as well as
the condenser and piping. At this point, all air
must be removed from the system (including each
pass). Close the vents in the evaporator chilled
water circuits.
4 Open all the valves in the evaporator chilled water
circuits.
5 If the evaporator was previously drained, vent and
fill the evaporator and chilled water circuit. When
all air is removed from the system (including each
pass), install the vent plugs in the evaporator
water boxes.
CAUTION
CAUTION: Insure that the oil sump
heaters have been operating for a
minimum of 24 hours before starting.
Failure to do so may result in equip-
ment damage.
6 Check the adjustment and operation of each
safety and operating control.
7 Close all disconnect switches.
8 Refer to the sequence for daily unit startup for the
remainder of the seasonal startup.
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