Protective Devices, Compressor Protection

Fig. 61 Ð Auxiliary Switch Adjustment

Moisture/Liquid Indicator Ð A clear ¯ow of liquid refrigerant indicates sufficient charge in the system. Bubbles indicate undercharged system or the presence of noncon- densables. Moisture in the system measured in parts per mil- lion (ppm) changes the color of the indicator:

Green Ð moisture below 45 ppm (dry) Chartreuse Ð 45 to 130 ppm (caution!) Yellow Ð moisture above 130 ppm (wet)

Change ®lter driers at the ®rst sign of moisture in the sys- tem. See Carrier Charging Handbook for more information.

IMPORTANT: Unit must be in operation at least 12 hours before moisture indicator can give an accu- rate reading. With unit running, indicating element must be in contact with liquid refrigerant to give a true reading.

Filter Drier Ð Replace whenever the moisture/liquid in- dicator shows moisture in the system.

Liquid Line Service Valve Ð Located immediately ahead of the ®lter drier, this valve has a 1/4-in. ¯are con- nection for ®eld charging. With the liquid circuit shut, the compressor can be used to pump the refrigerant down into the high side. The refrigerant can then be stored there by closing the compressor discharge valve.

Compressor Discharge Service Valve Ð Each compressor has one.

Compressor Suction Service Valve Ð Each com- pressor has one.

Protective Devices

COMPRESSOR PROTECTION

Overcurrent Ð Each compressor has one manual reset, cali- brated trip, magnetic circuit breaker. Do not bypass connec- tions or increase the size of the circuit breaker to correct trouble. Determine the cause and correct it before resetting the breaker.

Overtemperature Ð Each 06D compressor has an internal protector to protect it against excessively high discharge gas temperatures. Each 06E compressor has an external dis- charge gas thermostat. See Fig. 62. They will reset, but the circuit will automatically be locked out by the control board. Unit must be manually reset by interrupting control power.

Crankcase Heater Ð Each compressor has a crankcase heater to prevent absorption of liquid refrigerant by oil in the crank- case when the compressor is idle. Since 115-v power for the crankcase heaters is drawn from the unit control circuit, main unit power must be on for the heaters to be energized.

IMPORTANT: After a prolonged shutdown or service job, energize the crankcase heaters for 24 hours before starting the compressor.

Compressor Lockout Ð If any of the safeties (compressor internal thermostat [06D compressors only], high-pressure, or low-pressure) trip, or if there is a loss of power to the compressors, the compressors will be locked out. To reset DJ,DW units, manually move the thermostat setting. To re- set DK,DY,NB,NP units, consult the controls and trouble- shooting literature for the appropriate unit for details.

EVAPORATOR-FAN MOTOR PROTECTION Ð A manual reset, calibrated trip, magnetic circuit breaker protects against overcurrent. Do not bypass connections or increase the size of the breaker to correct trouble. Determine the cause and correct it before resetting the breaker.

CONDENSER-FAN MOTOR PROTECTION Ð Each condenser-fan motor is internally protected against over- temperature. They are also protected against a severe over- current condition by manual reset, calibrated trip, magnetic circuit breakers on a common circuit. As with the circuit break- ers, do not bypass connections or increase breaker size to correct trouble. Determine the cause and correct it before resetting the breaker.

HIGH- AND LOW-PRESSURE SWITCHES Ð See Fig. 62 for compressor mounting locations. Settings for these switches are shown in Table 11. If either switch trips, that refrigerant circuit will be automatically locked out by the controls. To reset, interrupt control power.

NOTE: When a pressure transducer is used, the low pres- sure trip point is the same as the low-pressure switch.

Relief Devices Ð All units have relief devices to pro- tect against damage from excessive pressures (i.e., ®re). These devices protect the high and low side.

NP034-074 specifications

The Carrier NP034-074 is an advanced rooftop unit designed for commercial heating, ventilation, and air conditioning (HVAC) applications. This unit is part of Carrier’s extensive range of rooftop units that are known for their energy efficiency, reliability, and innovative features. The NP034-074 series is particularly recognized for its robust performance in diverse environmental conditions, making it ideal for a variety of commercial building types.

One of the standout features of the NP034-074 is its high-efficiency compressor. Equipped with a scroll compressor, the unit offers enhanced performance and quieter operation compared to traditional reciprocating compressors. This design not only improves energy efficiency but also reduces operating costs over time. The unit is designed to meet or exceed the latest efficiency standards, ensuring that businesses can enjoy optimal indoor comfort while keeping energy consumption low.

The NP034-074 also integrates advanced control technologies that provide users with greater flexibility and ease of operation. The intuitive control system allows for precise temperature management and can be easily integrated with building automation systems. This enables users to monitor and adjust settings remotely, ensuring consistent and efficient climate control throughout the facility.

Another key characteristic of the NP034-074 is its robust construction. Built to withstand various weather conditions, the unit features a galvanized steel cabinet with a powder-coated finish for corrosion resistance. Its design also facilitates easy access for maintenance and service, which minimizes downtime and operational interruptions.

In terms of air distribution, the NP034-074 incorporates a powerful blower system that ensures even and effective airflow throughout the space. This design improves indoor air quality by enhancing ventilation while maintaining comfort levels. Additionally, the unit can be customized with options such as economizers and variable speed fans to optimize performance based on specific building needs.

The NP034-074 is a versatile and reliable choice for businesses looking to enhance their HVAC systems. With its combination of energy efficiency, advanced technology, and robust construction, this rooftop unit stands out as a top choice for commercial climate control solutions.