Carrier 48N User Manual download pdf (Page 73)

10. On-board storage of unit manufacturer's cus-

tomer user settings, retrievable from the

keypad.

11. RS485 communications capability (accessory

card source required).

12. Internal thermal overload protection.

13. 5% swinging (non-linear) chokes for harmonic

reduction and improved power factor.

14. All printed circuit boards shall be conformal

coated.

G. Outdoor-Air Hood Assembly:

Factory-installed motorized outdoor-air damper shall

allow intake of up to 100% nominal airflow (on units

not equipped with optional economizer).

H. Heating Section:

1. Induced-draft combustion type with energy sav-

ing direct spark ignition systems and redundant

main gas valves.

2. The heat exchanger shall be of the tubular sec-

tion type constructed of a minimum of 20-gage

steel coated with a nominal 1.4 mil aluminum-

silicone alloy for corrosion resistance.

3. Burners shall be of the in-shot type constructed

of aluminized steel.

4. Induced Draft Fans:

a. Direct-driven, single inlet, forward-curved

centrifugal type.

b. Statically and dynamically balanced.

c. Made from steel with a corrosion-resistant

finish.

5. High-corrosion areas such as flue gas collection

and exhaust areas shall be lined with corrosion-

resistant material.

6. All gas piping shall enter the unit cabinet at a

single location.

I. Refrigerant Components:

Unit shall be equipped with dual refrigerant circuits,

each containing:

1. Filter drier.

2. Moisture indicating sight glass.

3. Two electronic expansion valves.

4. Fusible plug.

J. Filter Section:

1. Mixed air filter section shall consist of 2-in.

thick, MERV 7 disposable fiberglass filters of

commercially available sizes. Optional pleated,

bag and cartridge filters shall be available. (See

special features section.)

2. Optional final filters with pre-filters shall be

available. (See special features section.)

K. Controls, Safeties, and Diagnostics:

1. Controls:

a. Control shall be accomplished through the

use of a factory-installed, microprocessor-

based control system and associated

electronic and electrical hardware. Control

system shall determine control sequences

through monitoring the following opera-

tional variables:

1) Day and Time.

2) Schedule (Unoccupied/Occupied).

3) Set points (Unoccupied/Occupied,

Economizer, Duct Pressure, others).

4) Space temperature.

5) Outdoor-air temperature.

6) Unit supply-air temperature.

7) Unit return-air temperature.

8) Supply-air fan status.

9) Economizer position.

10) Compressor suction and discharge

pressure.

11) Navigator™ display.

12) Accessory and/or field-supplied sensors,

function switches and/or signals.

b. Controls shall be capable of performing the

following functions:

1) Capacity control based on supply-air

temperature and compensated by rate

of change of return-air temperature

(VAV) or room temperature (CV).

Capacity control shall be accomplished

through the use of compressor staging

or optional variable output compressors.

2) Perform a quick test to check the status

of all input and output signals to the

control system using the Navigator™

display.

3) Control of integrated economizer opera-

tion, based on unit supply-air

temperature.

4) Supply fan volume control shall control

output from a variable frequency drive to

maintain duct static pressure at user-

configured set point (VAV). Static pres-

sure reset in conjunction with Carrier

communicating terminals to reduce sup-

ply fan power requirements. Control

system calculates the amount of supply

static pressure reduction necessary to

cause the most open damper in the sys-

tem to open more than the minimum

value (60%) but not more than the maxi-

mum value (90% or negligible static

pressure drop).

5) Heating control shall provide space tem-

perature control for unoccupied period

heating, morning warm-up sequence

and occupied period heating (when con-

figured). Leaving air temperature control

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Carrier 48N User Manual Page 73

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