McQuay IM 987 31
Mechanical Installation
Refrigerant Charge
Factory-installed DX coils are designed to use R-22. The total
charge per circuit is the sum of the following three values:
• Condenser section charge. Refer to manufacturer’s data.
• Evaporator coil charge.
• Charge for length of interconnecting piping installed by
field.
Note: Factory-installed DX coils are intended for one
refrigerant circuit on unit size 800C and two refrigerant
circuits containing identical weights of refrigerant on all
other sizes. The values shown in Ta ble 8 and Table 9 are
for each circuit.
Note: The total operating charge per circuit should not exceed
the pumpdown capacity per circuit.
Note: * The RDS 802C unit has two refrigerant circuits.
Unit Piping
Condensate Drain Connection
• The unit is provided with a 1.5" male NPT condensate drain
connection. Refer to certified drawings for the exact
location. For proper drainage, level the unit and drain pan
side to side and install a P-trap
• Units may have positive or negative pressure sections. Use
traps in both cases with extra care given to negative pressure
sections. In Figure 57, dimension “A” should be a minimum
of 8" (203 mm). As a conservative measure to prevent the
cabinet static pressure from blowing or drawing the water
out of the trap and causing air leakage, dimension A should
be two times the maximum static pressure encountered in
the coil section in inches wc.
• Draining condensate directly onto the roof may be
acceptable; refer to local codes. Provide a small drip pad of
stone, mortar, wood, or metal to protect the roof against
possible damage.
• If condensate is piped into the building drainage system,
pitch the drain line away from the unit a minimum of 1/8"
per foot. The drain line must penetrate the roof external to
the unit. Refer to local codes for additional requirements.
Sealed drain lines require venting to provide proper
condensate flow.
• Where the cooling coils have intermediate condensate pans
on the face of the evaporator coil, copper tubes near both
ends of the coil provide drainage to the main drain pan.
Check that the copper tubes are in place and open before the
unit is put into operation.
• On units with staggered cooling coils, the upper drain pan
drains into the lower coil drain pan through a copper tube
near the center of the drain pan. Check that this tube is open
before putting the unit into operation and as a part of routine
maintenance.
• Because drain pans in any air conditioning unit have some
moisture in them, algae, etc. will grow. Periodically clean to
prevent this buildup from plugging the drain and causing the
drain pan to overflow. Clean drain pans to prevent the spread
of disease. Cleaning should be performed by qualified
personnel
.
Figure 33: Condensate Drain Connection
Gas Piping
See the “Installation” section of the gas-fired furnace
installation manual, Bulletin No. IM 684 or 685.
Table 8: Approximate DX Coil Refrigerant Charge Per
Circuit
Unit size
DX Coil R-22 charge (lbs./circuit)
Flat coil Staggered coil
047C 3 x no. of DX rows 3.5 x no. of DX rows
077C 5 x no. of DX rows 6.5 x no. of DX rows
Table 9: Approximate Refrigerant Charge Per Circuit
Unit size Evaporator coil (lbs/ckt/coil row)
802 3.30
802C* 2.45
WARNING
Drain pans must be cleaned periodically.
Material in uncleaned drain pans can cause disease.
Cleaning should be performed by qualified personnel.
S t a t i c P r e s s u r e " P "
( i n . w . o . )
D r a i n P a n
4 " ( 1 0 2 m m )
M i n i m u m
" A "
8 " ( 2 0 3 m m )
M i n . o r 2 x " P "
M i n i m i z e T h i s
D i m
e n s i o n
V i e w A
N o t e : D r a i n l i n e m u s t
n o t b e r u n h i g h e r
t h a n t h i s l e v e l
C o p p e r T u b e
( o n e e a c h e n d o f c o i l )
S e e V i e w " A "
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