Table 12. Circuit operation-top level mode - waiting to start
Circuit Description
Top Level Mode
Waiting to Start The circuit is going through the necessary steps to allow the lead circuit to start.
Waiting to Start Sub Modes
Prepositioning EXV
The circuit will wait for the time it takes the EX
V to get to its commanded pre-
position prior to starting the compressor. This is typically a relatively short delay
and no countdown timer is necessary (less than 15 seconds).
Note: This does not occur during EXV pre-position but is not necessarily required
as the time
is short and the top level mode is adequate to explain that the startup
sequence is in process.
Table 13. Circuit operation-top level mode - running
Circuit Description
Top Level Mode
Running The compressor on the given circuit is currently running.
Running Sub Modes
Comfort Purge
A Comfort Purge cycle is entered when compressors have been running on the
reheat circ
uit but no reheat is commanded. Therefore, reheat has been inactive
and the reheat modulating valve has been closed.
Dehumidification Purge
A Dehumidification Purge cycle is entered when compressors have been running
o
n the reheat
circuit, “standalone” dehumidification control is active and reheat
has been active with the modulating valve having been opened.
38 RT-SVP011E-EN
TD7 Display
Table 14. Circuit operation-top level mode - running-limit
Circuit Description
Top Level Mode
Running – Limit
The circuit is currently running however the operation of the unit/compressors
is being actively li
mited by the controls. Further information is provided by the
sub-mode. See the section below regarding criteria for annunciation of limit
modes.
Running – Limit Sub Modes
Coil Purge
A 3 minute Coil Purge is in process to reclaim any logged oil fro
m the condenser
or reheat coils.
Compressor Involute Pressure Limit
If compressors on the circuit are energized and the compressor involute pressure
differential
limit is in the hold region or unload region.
Compressor Startup Speed Limit
This applies to the variable speed compressor and enforces a maximum speed
li
mit for a fixed ti
me period following startup. During normal operation, the speed
range limits are determined based on unit type, efficiency, capacity stage and
other limit controls. The maximum speed limit following every startup is treated
as a special case to help provide the best possible oil quality.
Discharge Pressure Limit
The circuit capacity is prevented from loading or has unloaded due to high
di
scharge pressure.
Frost Protection Limit
This is a circuit level protection and is active whenever one or more compressors
on a circuit are runni
ng. Each circuit will compare its Saturated Suction
Temperature to various criteria. Depending on the severity of the coil frost
potential this protection will limit loading or unload the circuit capacity in an
attempt to minimize the frost.
High Discharge Pressure Limit
This circuit-level feature prevents a circuit shutdown when the discharge
pr
essure approac
hes the high-pressure cutout switch setting by decreasing
compressor capacity. Limit control action modifies the normal capacity
modulation and staging commands to decrease capacity by reducing compressor
modulation or staging off compressors on circuits with high discharge pressure.
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