Unit Functions
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IOM 1207-6 • TRAILBLAZER
®
MODEL AGZ CHILLERS
Table 53: Stage Limits - Six Compressors
Demand Limit Signal
(%)
Demand Limit Range
(mA)
Stage
Limit ≥ 83.3%
Limit ≥ 17.3 mA
1
83.3% > Limit ≥ 66.7% 17.3 mA > Limit ≥ 14.7 mA
2
66.7% > Limit ≥ 50%
14.7 mA > Limit ≥ 12 mA
3
50% > Limit ≥ 33.3%
12 mA > Limit ≥ 9.3 mA
4
33.3% > Limit ≥ 16.7% 9.3 mA > Limit ≥ 6.7 mA
5
16.7% > Limit
6.7 mA > Limit
6
Network Limit
The maximum unit capacity can be limited by a network signal.
This function is only enabled if the control source is set to
network. The maximum unit capacity stage is based on the
network limit value received from the BAS and is determined
as shown in the following tables:
Table 54: Stage Limits - Four Compressors
Network Limit
Stage
Limit ≥ 100%
4
100% > Limit ≥ 75%
3
75% > Limit ≥ 50%
2
50% > Limit
1
Table 55: Stage Limits - Six Compressors
Network Limit
Stage
Limit ≥ 100%
6
100% > Limit ≥ 83.3%
5
83.3% > Limit ≥ 66.7%
4
66.7% > Limit ≥ 50%
3
50% > Limit ≥ 33.3%
2
33.3% > Limit
1
Maximum LWT Pulldown Rate
The maximum drop rate for the leaving water temperature shall
be limited by the Maximum Pulldown Rate set point only when
the unit mode is Cool.
If the rate exceeds the set point, no more compressors can
be started until the pulldown rate is less than the set point.
Running compressors will not be stopped as a result of
exceeding the maximum pulldown rate.
High Ambient Limit
On units configured with single point power connections, the
maximum load amps could be exceeded at high ambient
temperatures. If the power connection is single point, and the
outdoor air temperature OAT is greater than 46.6°C (115.9°F),
the high ambient limit becomes active. This limit will be
removed when the OAT drops back down to 45.56°C (114°F).
The max operating ambient temperature is 51.6°C (125°F).
When the limit is active, the unit is allowed to run all but one
compressor. So it will inhibit the unit from loading if all but one
compressor is on, and it will shut down a compressor if all
compressors are running.
RapidRestore
®
Option
RapidRestore
®
is an option that can be added to Trailblazer
®
chillers. The general purpose of the option is to allow the
capability to restart more quickly and to load faster than normal
operation.
Enabling
The RapidRestore
®
option shall be enabled via the
RapidRestore
®
set point and requires the optional module.
Doing so will require the following to be true:
• RapidRestore
®
module is present at address 22
• DI1 on the RapidRestore
®
module has a signal
If the DI1 input loses the signal or the RapidRestore
®
module
is no longer communicating, then the option will be disabled in
the chiller.
Operation Following Power Cycle
The chiller will enter RapidRestore
®
upon powering up when
the following conditions are met:
• RapidRestore
®
is enabled
• Power failure lasts less than the value of the Max Power
Failure Time set point
• Power failure lasts at least one second (shorter power
loss may result in unpredictable operation)
• Unit is enabled
When RapidRestore
®
is triggered, the time value used for the
evaporator recirculation time will be limited to 110 seconds
or less. The evaporator recirculation time set point will not be
changed. Only the value used in the evaporator state logic will
be limited, and only if the set point exceeds the 110 second
limit.
This action will ensure that the chiller is ready to start after the
motor protection module delay has expired.
Time to Start
The compressor manufacturer requires a minimum two minute
delay after power on until a compressor should be started,
which is to ensure proper operation of the motor protection
modules. Unit controller boot time is about 10 seconds, so a
delay of 110 seconds will start upon completing boot up. After
this delay, the two minute manufacturer requirement will be
satisfied.
After the 110 second delay, the first circuit to start will enter the
preopen state, which takes five seconds. The end result is that
the first compressor should start approximately 125 seconds
after power is restored to the chiller.
Current software has a delay of 150 seconds after bootup is
complete before the first circuit can start. The software will be
