AAON CA-25 - Manual (Page 4)

4
GENERAL
All refrigeration systems are factory assembled, includ-
ing a holding charge of R-22, and tested. On 13 - 25 ton
units the refrigerant system includes dual condenser
coils providing two stage cooling. These systems are
provided with liquid line filter driers and fully hermetic
compressors. Compressors are equipped with a posi-
tive pressure forced lubrication system and crankcase
heater. The air cooled condenser coil(s) is constructed
of copper tubes with aluminum fins (copper fins op-
tional), the air is pulled through with steel propeller
fans.
All CA Condensing units have factory furnished liquid
and suction line shutoff valves. The pipe sizes must be
selected to meet the actual installation conditions
and not simply based on the connection sizes at the
evaporator and/or condensing unit.
The refrigeration section of these appliances has been
listed by E.T.L. as meeting the applicable provisions of
UL 1995, CAN/CSA C22.2, No. 236-Second Edition.
NOTE: Crankcase Heater Operation
The 8 through 25 ton sizes are equipped with a crank-
case heater, which should be energized at least 24
hours prior to setting the thermostat for cooling opera-
tion with the compressor.
This section is not intended to provide all the informa-
tion required by the designer or installer of the refriger-
ant piping between the condensing units and the low
side components. The appropriate sections of the
ASHRAE Guide and the ASME standards should be
used for final information.
The piping between the condenser and low side must
assure:
• minimum pressure drop
• continuous oil return
• prevention of liquid refrigerant slugging or carryover.
Acceptable system design and installation will include
consideration as follows:
Interconnecting Piping Summary
• piping from the condensing unit to the indoor air
handler is the responsibility of the installing con-
tractor.
• only clean "ACR" tubing should be used.
• condensing units are provided with in-line shutoff
valves on both the liquid and suction lines. These
should remained closed until the system is ready
for start-up.
• piping should conform to generally accepted
practices and codes.
• care must be taken not to cross the circuits on
multiple circuit systems.
▲
! IMPORTANT
The Clean Air Act of 1990 bans the intentional
venting of refrigerant (CFC's and HCFC's) as of
July 1, 1992. Approved methods of recovery,
recycling or reclaiming must be followed.
Fines and/or incarceration may be levied for
non-compliance.
REFRIGERANT PIPING
• once piped, the interconnecting piping and air
handler MUST BE evacuated to 50 microns or less;
leak checked and charged with R22 refrigerant.
• open the shut off valves.
• run unit, check rotation of compressors using
refrigerant gauges.
• check super heat and subcooling; subcooling
should be 10-13
°
F, evaporator superheat should
be 10-15
°
F. Also check the compressor discharge
line superheat. It should be at least 60
°
F.
• make sure airhandler thermal expansion valve
bulb is mounted with good thermal contact on
the correct suction line on a horizontal section,
close to the evaporator in the 4 or 8 o'clock
position and insulated.
• the suction line should be insulated for its entire
length.
SUCTION LINE
The suction line pipe size should be selected to have
a maximum pressure drop of 3 PSI for the equivalent
length of piping that is used. This corresponds to
approximately 2
°
F with R22.
Any vertical suction risers should be checked to con-
firm that oil will be returned to the compressor. (Use
the following tables for pipe sizing information).
All suction lines must be pitched in the direction of flow
and supported to maintain their position.
Fully insulated piping must be used between the
evaporator and the condensing unit. A suction accu-
mulator is not included as part of the CA condensing
unit and must be field furnished and installed if re-
quired by job conditions.
R22 SUCTION LINE CAPACITY
Pressure Loss = 3 PSI (2
°
F) at 40
°
F saturated suction
NOTE: Pressure loss, PSI/100 feet of equivalent line length
due to line friction. (Corresponding change in R22 satura-
tion temperature.)
LINE SIZE - inches MAX. TONS / COMPRESSOR
5/8" 1.1
7/8" 2.9
1 1/8" 5.8
1 3/8" 10.1
1 5/8" 16.0