Carrier 30XA080-500 Controls, Start-Up, Operation, Service And Troubleshooting Instructions page 21

Override #13: Minimum On/Off and Off/On Time Delay --
Whenever a capacity change has been made, the control will
remain at this capacity stage for the next 90 seconds. During
this time, no capacity control algorithm cCdculations will be
made. If the capacity step is a compressor, an additional
90-second delay is added to the previous hold time (see Over-
ride #227. This override allows the system to stabilize before
another capacity stage is added or removed. If a condition of a
higher priority override occurs, the higher priolity override will
take precedence. Operating Mode 10 (MDI 0) will be in effect.
Override #14: Slow Change Override -- This override pre-
vents compressor stage changes when the leaving temperature
is close to the control point and slowly moving towards the
control point.
Override #15: System Manager Capacity Control -- If a
Chillervisor module is controlling the unit and the Chillervisor
module is controlling multiple chillers, the unit will increase
capacity to attempt to load to the demand limited v_due.
Override #16: Circuit A High Pressme Override
Override #17: Circuit B High Pressure Override
Override #18: Circuit C High Pressure Override -- This over-
ride attempts to avoid a high pressure failure. The algorithm is
run evely 4 seconds. If the Saturated Condensing Temperature
for the circuit is above the High Pressure Threshold (Configu-
ration--+ SERV--+HP.TH) then the position of slide valve will
be unloaded.
Override #19: Standby Mode -- This override algorithm will
not allow a compressor to run if the unit is in Standby mode,
(Run Status--)VIEW--_HC.ST=2).
Override #22: Minimum On Time Delay -- In addition to
Override #13 Minimum On/Off and Off/On Time Delay, for
compressor capacity changes, an additional 90-second delay
will be added to Override #13 delay. No compressor will be
deenelgized until 3 minutes have elapsed since the last com-
pressor has been turned ON. When this override is active, the
capacity control _dgorithm calculations will be perf(mned, but
no capacity reduction will be made until the timer has expired.
A control with higher precedence will override the Minimum
On Time Delay.
Override #23: Circuit A Low Saturated Suction
Temperature in Cooling
Override #24: Circuit B Low Saturated Suction
Temperature in Cooling
Override #25: Circuit C Low Saturated Suction Tempera-
ture in Cooling -- If the circuit is operating in an gu'ea close to
the operational limit of the compressol: the circuit capacity will
remain at the same point or unload to raise the saturated suction
temperatme. This _dgorithm will be active if at least 1 comples-
sot in the circuit is on and one of the following conditions is tree:
1. Saturated Suction Temperature is less than the Brine
Fleeze Setpoint (Configuration --_;ERV--cLOSP) - 6 ° F
(3.3 ° C).
2. Saturated Suction Telnperature is less than the Brine
Fleeze Setpoint (Configuration--cSERV--cLOSP) and
the circuit approach (Leaving Water Temperature - Satu-
rated Suction Temperature) is greater than 15 ° F (8.3 ° C)
and the Circuit Supoheat (Discharge Gas Temperatme -
Saturated Discharge Temperatme) is greater than 25° F
(13.9 ° C).
NOTE: The freeze set point is 34 F (1.1 C) for fresh
water systems (Configuration ---_S'ERV---_FLUD=I). The
freeze set point is Brine Freeze Set Point (Conjqguration
--+SERV--+LOSP), for Medium Temperature Brine
systems (Configuration ---_SERV---_FLUD=2).
If any of these conditions gue met, the appropriate operating
mode, 21 (Circuit A), 22 (Circuit B) or 23 (Circuit C) will be in
effect.
Override #26: Circuit A High Discharge Gas Override
Override #27: Circuit B High Discharge Gas Override
Override #28: Circuit C High Discharge Gas Override --
When the temperature is above the limit curve minus 2 ° F
(1.1 ° C) increase in capacity will not be allowed. This ovemde
will remain active until the DG_" goes below the limit curve by
-3 ° F (-1.7 ° C).
OvelTide #34: Circuit A Low Refi'igerant Charge
Override #35: Circuit B Low Refiigerant Charge
Override #36: Circuit C Low Refrigerant Charge -- The ca-
pacity override attempts to protect the compressor from start-
ing with no refiigemnt in the circuit. This algorithm runs only
when the circuit is not operational (no compressors are ON).
There are several criteria that will enable this override:
1. The saturated suction temperature or saturated dischmge
temperature is less than -13 F (-10.6 C).
2. All of these conditions must be true:
a. The saturated suction temperature or saturated
discharge temperature is less than leaving water
temperature by more than 5.4 ° F (3.0 ° C).
b. Saturated suction temperature or saturated dis-
charge temperature is less than 41 F (5 C).
c. Outdoor air temperature is less than 32 F (0 ° C).
d. Saturated suction temperature or saturated discharge
temperature is less than the outdoor air temperature
by more than 5.4 ° F (3.0 ° C).
3. All of these conditions must be true:
a. The saturated suction temperature or saturated
discharge temperature is less than leaving water
temperature by more than 5.4° F (3.0° C).
b. Saturated suction temperature or saturated dis-
charge temperature is less than 41 F (5 C).
c. Saturated suction temperature or saturated dis-
charge temperature is less than the brine freeze
point (Configuration--+SERV--+LOSP) by more
than 6° F (3.3° C).
NOTE: The freeze set point is 34 F (1.1 C)
for fresh water systems
(Configuration---)SERV
--+FLUD=I). The freeze set point is brine freeze
set point (Configuration--_SERV--_LOSP), for
medium temperature brine systems (Configura-
tion --_SER V--)FLUD=2 ).
All of these conditions must be true:
a. The saturated suction temperature or saturated
discharge temperature is less than leaving water
temperature by more than 5.4 ° F (3.0 ° C).
b. Saturated suction temperature or saturated discharge
temperature is less than 41 F (5 C).
c. Saturated suction temperature or saturated discharge
temperature is less than the outdoor air temperature
by more than 9 ° F (5 ° C).
If any of these conditions 1,2, 3 or 4 are met, the appropri-
ate operating mode, 21 (Circuit A), 22 (Circuit B) or 23
(Circuit C) will be in effect.
Override #41 : Circuit A High Current Override
Override #42: Circuit B High Current Override
Override #43: Circuit C High Current Override
This override attempts to avoid an overcurrent failure. The
_dgorithm is run every 4 seconds. If the compressor current is
greater than 79% of must trip amps (MTA) but less than 85%
MTA then the capacity will be held at current capacity. If the
compressor current is greater than 85% MTA then capacity
will be reduced by repositioning the slide valve until the
current is less than 85% MTA (Configuration--cUNIT--€
MTA.X).
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