York 251934-YTG-J-0910 - Manual (Page 10)

251934-YTG-J-0910
10 Johnson Controls Unitary Products
the service factor. Units shall be designed not to operate above
service factor. Fan wheel shall be double-inlet type with
forward-curved blades, dynamically balanced to operate
smoothly throughout the entire range of operation. Airflow
design shall be constant air volume.
A variable air volume (VAV) option using a variable frequency
drive (VFD) is available for applications requiring a constant
supply duct static pressure. Units equipped for VAV shall be
controlled by a duct pressure transducer with a 0 - 5” WC
pressure range. The pressure transducer shall provide a 0 - 5
VDC output signal to a VAV control board which, in turn shall
provide a 2 - 10 VDC speed reference signal to the VFD. The
VAV control board shall operate using factory-installed Supply
Air, Return Air and Outside Air Temperature Sensors. Units
equipped with VFD’s shall have factory-installed manual bypass
as an option.
Outdoor (Condenser) Fan Assembly
The outdoor fans shall be of the direct-driven propeller type,
discharge air vertically, have aluminum blades riveted to
corrosion resistant steel spider brackets and shall be
dynamically balanced for smooth operation. The 4 outdoor fan
motors shall be totally enclosed with permanently lubricated
bearings, internally protected against overload conditions and
staged independently.
Refrigerant Components
Compressors:
a. Shall be Scroll compressors internally protected with
internal high-pressure relief and over temperature
protection.
b. Shall have internal spring isolation and sound muffling to
minimize vibration and noise, and be externally isolated
on a dedicated, independent mounting.
Coils:
a. Evaporator and condenser coils shall have aluminum
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 foreign
matter.
c. Accessible service gage connections on both suction
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 four 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-voltage
control circuit protected by a resettable circuit breaker on
the 24-volt transformer side.
b. Unit shall incorporate a lockout circuit which provides
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 (ZJ/ZR/ZF***N Models)
Shall be designed with induced draft combustion with post purge
logic and energy saving direct spark ignition, redundant 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 following 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 independent
stages of capacity.