Carrier SUPRA 950Mt - Lead Compartment Decision; Pulse Sequence; Figure 4.1 Temperature Controller Op Seq (Frozen Range) Controller Set Point below +10°F (-12°C)

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b. STANDBY Mode
Automatic Start:
The DER is energized via N2 output.
• Prevents activation of engine run solenoid and fuel pump
• Standby motor contactor is energized
The RR is energized. Electrical power is supplied to the standby motor for starting.
c. Temperature Control
When a compartment enters COOL mode, the cool relay (CR) is energized, while the hot gas (HGR) and electric
heat relays (EHR) are de-energized. This allows refrigerant to flow to the compartment’s evaporator.
d. HEAT Mode
When a compartment enters the HEAT mode, it will either use hot gas, run an electric heater, or both. If the com-
partment is the lead compartment, it will heat with hot gas as long as no other compartment is cooling.
e. NULL Mode
When a compartment enters the NULL mode, the cool, hot gas, and electric heat relays are disabled.
4.1.5 Lead Compartment Decision
As long as the compressor is running, at least one compartment must accept refrigerant or hot gas. The unit may
need to override the NULL mode in a compartment to force the compartment to either cool or hot gas heat,
depending on the compartment’s error offset. The compartment that is overridden is called the lead compartment.
The criteria used to decide which compartment should be lead at any given time is as follows:
If all active compartments are calling for the null mode, then some compartments must be forced to accept flow
from the compressor. In this situation, the compartment with the highest set point will be chosen and will become
the lead compartment.
4.1.6 Pulse Sequence
There is a sequence available for each compartment to use either pulse heating or cooling. A 30-second period is
divided into three 10-second intervals, one for each compartment. Based on these 10-second intervals, each com-
partment uses a 50 percent duty cycle, or five seconds of refrigerant flow, followed by five seconds of no refrigerant
flow. Following this, there is an additional 20-second period of no refrigerant flow for each compartment and the
cycle repeats.
Figure 4.1 Temperature Controller Op Seq (Frozen Range) Controller Set Point Below +10°F (-12°C)
3.6 F (2.0 C)
í0.9
F (í0.5 C)
3.6
F (0.8 C)
í2.7
F (í1.5 C)
í3.6
F (í2.0 C)
Set point
4 Cyl. Cool
4 Cyl. Heat
4 Cyl. Cool
í1.4
F (í0.8 C)
6 Cyl. Heat
6 Cyl. Cool
For Start-Stop, the engine will go to an OFF
cycle when the temperature for all
compartments with set point in the
perishable range are within 1.0 F (0.5 C)
of set point and all compartments in the
Frozen range are within + 1.0 F (0.5 C)
or lower than set point.