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262259-YTG-B-0107
38 Unitary Products Group
bearings, internally protected against overload conditions and
staged independently.
REFRIGERANT COMPONENTS
Compressors:
a. Shall be Scroll (25T only) compressors internally
protected with internal high-pressure relief and over
temperature protection.
b. Shall have internal spring isolation and sound muf-
fling to minimize vibration and noise, and be exter-
nally isolated on a dedicated, independent
mounting.
Coils:
a. Evaporator and condenser coils shall have alumi-
num plate fins mechanically bonded to seamless
internally enhanced copper tubes with all joints
brazed. Special Phenolic coating shall be available
as a factory option.
b. Evaporator and Condenser coils shall be of the
direct expansion, draw-thru, design.
Refrigerant Circuit and Refrigerant Safety Components shall
include:
a. Balance-port thermostatic expansion valve with
independent circuit feed system.
b. Filter drier/strainer to eliminate any moisture or for-
eign matter.
c. Accessible service gage connections on both suc-
tion and discharge lines to charge, evacuate, and
measure refrigerant pressure during any necessary
servicing or troubleshooting, without losing charge.
d. The refrigeration system shall provide at least 15° F
of sub-cooling at design conditions.
e. All models shall have two independent circuits.
f. Hot gas bypass option shall be factory-installed on
compressor #1 discharge line to provide cooling in
low-load applications. HGBP shall be a standard
feature on VAV models and an optional feature on
CV models.
UNIT CONTROLS
a. Unit shall be complete with self-contained low-volt-
age control circuit protected by a resettable circuit
breaker on the 24-volt transformer side.
b. Unit shall incorporate a lockout circuit which pro-
vides reset capability at the space thermostat or
base unit, should any of the following standard
safety devices trip and shut off compressor.
c. Loss-of-charge/Low-pressure switch.
1. High-pressure switch.
2. Freeze-protection thermostat, evaporator coil. If
any of the above safety devices trip, a LED
(light-emitting diode) indicator shall flash a
diagnostic code that indicates which safety
switch has tripped.
d. Unit shall incorporate "AUTO RESET" compressor
over temperature, over current protection.
e. Unit shall operate with conventional thermostat
designs and have a low voltage terminal strip for
easy hook-up.
f. Unit control board shall have on-board diagnostics
and fault code display.
g. Standard controls shall include anti-short cycle and
low voltage protection, and permit cooling operation
down to 0 °F.
h. Control board shall monitor each refrigerant safety
switch independently.
i. Control board shall retain last 5 fault codes in non
volatile memory, which will not be lost in the event of
a power loss.
GAS HEATING SECTION (DM***N MODELS)
Shall be designed with induced draft combustion with post
purge logic and energy saving direct spark ignition, redun-
dant main gas valve. Ventor wheel shall be constructed of
stainless steel for corrosion resistance. The heat exchanger
shall be of the tubular type, constructed of T1-40 aluminized
steel for corrosion resistance and allowing minimum mixed
air entering temperature of 25° F. Burners shall be of the in-
shot type, constructed of aluminum coated steel and contain
air mixture adjustments. All gas piping shall enter the unit
cabinet at a single location through either the side or curb,
without any field modifications. An integrated control board
shall provide timed control of evaporator fan functioning and
burner ignition. Heating section shall be provided with the fol-
lowing minimum protection:
a. Primary and auxiliary high-temperature limit
switches.
b. Induced draft motor speed sensor.
c. Flame roll out switch (automatic reset).
d. Flame proving controls. Unit shall have two inde-
pendent stages of capacity.
ELECTRIC HEATING (DM***C/E MODELS)
Nickel chromium electric heating elements shall be provided
as required by the application with 1 or 2 stage control, as
required, from 13.5 KW to 72 KW capacities. The heating
section shall have a primary limit control(s) and automatic
reset to prevent the heating element system from operating
at an excessive temperature. Units with Electric Heating shall
be wired for a single point power supply with branch circuit
fusing (where required).
UNIT OPERATING CHARACTERISTICS
Unit shall be capable of starting and running at 125° F
outdoor temperature, exceeding maximum load criteria of
ARI Standard 340/360. The compressor, with standard
controls, shall be capable of operation down to 0° F outdoor