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Carrier 69NT20-531-300 manual Modes of Operation

Models: 69NT20-531-300

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3.2.2 Operational Software (Function codes)

The Operational Software is the actual operation programming of the controller which activates or deactivates components in accordance with current unit operating conditions and operator selected modes of operation.

The programming is divided into function Codes. Some of the codes are read only while the remaining codes may be user configured. The value of the user configurable codes can be assigned in accordance with user desired mode of operation. A list of the function codes is provided in Table 3-5.

To access the function codes, perform the following:

a. Press the CODE SELECT key, then press an arrow key until the left window displays the desired code number.

b. The right window will display the value of this item for five seconds before returning to the normal dis- play mode.

c. If a longer time is desired, press the ENTER key to extend the time to 30 seconds.

3.3 MODES OF OPERATION

The Operational Software responds to various inputs. These inputs come from the temperature and pressure sensors, the temperature set point, the settings of the the configuration variables and the function code assignments. The action taken by the Operational Software will change if any one of the inputs changes. Overall interaction of the inputs is described as a “mode” of operation. The modes of operation include, perishable (chill) mode and frozen mode. Descriptions of the controller interaction and modes of operation are provided in the following sub paragraphs.

3.3.1 Temperature Control -- Perishable Mode

With configuration variable CnF26 (Heat Lockout Temperature) set to -10_C the perishable mode of operation is active with set points at or above -10_C (+14_F). With the variable set to -5_C, the perishable mode is active at or above -5_C (+23_F). Refer to Table 3-4.

When in the perishable mode the controller maintains the supply air temperature at set point, the SUPPLY indicator light will be illuminated on the display module and the default reading on the display window will be the supply temperature sensor reading.

When the supply air temperature enters the in-range temperature tolerance (as selected at function code Cd30), the in-range light will energize.

3.3.2 Defrost Interval

Function code Cd27 may be operator set to initiate defrost at intervals of 3, 6, 9, 12 or 24 hours. It may also be set to OFF (no defrost). The factory default is 12 hours. (Refer to Table 3-5).

3.3.3 Failure Action

Function code Cd29 may be operator set to allow continued operation in the event the control sensors are reading out of range. The factory default is full system shutdown. (Refer to Table 3-5).

3.3.4 Generator Protection

Function codes Cd31(Stagger Start, Offset Time) and Cd32 (Current Limit) may be operator set to control start up sequence of multiple units and operating current draw. The factory default allows on demand starting (no delay) of units and normal current draw. Refer to Table 3-5.

3.3.5Compressor High Temperature, Low Pres- sure Protection.

The controller monitors compressor suction and discharge temperatures and pressures. If the discharge temperature exceeds a certain limit, the liquid injection valve is opened to provide sufficient liquid refrigerant flow into the economizer line to reduce the discharge temperature. If the liquid injection is unable to reduce the discharge temperature sufficiently and the temperature exceeds the allowed limit, the compressor will cycle off on a 3 minute timer. The compressor will also cycle off in a similar manner if the suction pressure falls below the allowed limit. Condenser and evaporator fans continue to operate during the compressor off cycle.

3.3.6 Perishable Mode -- Conventional

The unit is capable of maintaining supply air temperature to within ¦0.25_C (¦0.5_F) of set point. Supply air temperature is controlled by positioning of the suction modulation valve (SMV), cycling of the compressor and cycling of the heaters.

When cooling from a temperature that is more than 2.5_C (4.5_F) above set point, the system will be in the perishable pull down mode. It will be in economized operation with a target SMV position of 100% open. However, pressure and current limit functions may restrict the valve, if either exceeds the preset value.

Once set point is reached, the unit will transition to the perishable steady state mode. This results in unloaded operation with some restriction of the SMV. The SMV will continue to close and restrict refrigerant flow until the capacity of the unit and the load are balanced.

If the SMV is at minimum modulation, the controller has determined that cooling is not required, or the controller logic determines suction pressure is at the low pressure limit, the unit will transition to the perishable idle mode. The compressor is turned off and the evaporator fans continue to run to circulate air throughout the container. If temperature rises above set point +0.2_C, the unit will transition back to the perishable steady state mode

If the temperature drops to 0.5_C (0.9_F) below set point, the unit will transition to the perishable heating

T-309

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Carrier 69NT20-531-300 manual Modes of Operation
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69NT20-531-300 specifications

The Carrier 69NT20-531-300 is a cutting-edge rooftop unit designed to meet the demanding requirements of commercial heating and cooling applications. This model embodies Carrier’s commitment to energy efficiency, reliability, and advanced technological features that enhance indoor comfort while minimizing operational costs.

One of the standout features of the Carrier 69NT20-531-300 is its high energy efficiency. It is equipped with advanced compressor technology that optimizes performance while reducing energy consumption. This ensures that businesses can maintain a comfortable indoor climate without incurring exorbitant utility bills. With a high Seasonal Energy Efficiency Ratio (SEER) and Energy Efficiency Ratio (EER), users can expect not only enhanced comfort but also significant cost savings over time.

The cooling capabilities of the 69NT20-531-300 are complemented by its robust heating options. This unit utilizes a gas heat exchanger, ensuring quick and even heating throughout the space. The combination of cooling and heating capabilities in one compact unit makes it a versatile choice for various applications, including retail spaces, offices, and warehouses.

In addition to its impressive performance specifications, the Carrier 69NT20-531-300 incorporates innovative technologies that further enhance its functionality. The unit comes with advanced controls, allowing for precise temperature regulation and zoning capabilities. This ensures that different areas of a building can maintain their desired temperatures based on usage, improving overall energy efficiency.

Durability is another hallmark of the Carrier 69NT20-531-300. The unit is constructed with high-quality materials and features a weather-proof cabinet that protects it from the elements, ensuring long-term reliability even in harsh conditions. Furthermore, its modular design simplifies maintenance, making it easy for technicians to access critical components.

The 69NT20-531-300 is also designed with low noise operation in mind. It employs sound-dampening technology to ensure that operations are quiet, making it an ideal choice for locations where noise reduction is a priority, such as schools or healthcare facilities.

Overall, the Carrier 69NT20-531-300 stands out as a premier choice for businesses looking for an efficient, reliable, and feature-rich rooftop HVAC unit. Its blend of energy efficiency, advanced technology, and durability positions it as a leader in commercial heating and cooling solutions, making it a valuable investment for any commercial property.