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Piping Recommendations
Use type K or L clean copper tubing. Thoroughly clean
1
or braze all joints with high temperature solder. Base
piping sizes on temperature/pressure limitations as
recommended in the following paragraphs. Under no
circumstances should pipe size be based strictly upon
coil or condensing unit piping connection size.
Do not exceed suction line piping pressure drop
2
equivalent to 2°F (1°C), 3 psi (20.7 kPa) per 100 feet
(30.5 m) of equivalent pipe length. After the suction line
size is determined, check the vertical suction risers to
verify that oil will be carried up the riser and back to the
compressor. Pitch the suction line(s) in the direction of
refrigerant flow and make sure they are adequately
supported. Lines should be free draining and fully
insulated between the evaporator and the compressor.
Install a trap on the vertical riser to the compressor.
To determine the minimum tonnage required to carry oil
3
up suction risers of various sizes, check the vertical
suction risers using
Table
the unit cabinet to prevent condensation.
Table 6: Minimum Tonnage (R-22) to Carry Oil Up Suction
Riser at 40°F Saturated Suction
Line size O.D.
1 1/8"
1 3/8"
1 5/8"
2 1/8"
2 5/8"
3 1/8"
3 5/8"
4 1/8"
Size the liquid line for a pressure drop not to exceed
4
the pressure equivalent of 2°F (1°C), 6 psi (41.4 kPa)
saturated temperature.
Leak Testing
In the case of loss of the nitrogen holding charge, the unit
should be checked for leaks prior to charging the complete
system. If the full charge was lost, leak testing can be done by
charging the refrigerant into the unit to build the pressure to
approximately 10 psig and adding sufficient dry nitrogen to
McQuay IM 987
6. Insulate suction lines inside
Minimum tonnage
1.5
2.5
3.8
7.6
13.10
20.4
29.7
41.3
Mechanical Installation
bring the pressure to a maximum of 125 psig. The unit should
then be leak tested with halide or electronic leak detector.
After making any necessary repair, the system should be
evacuated as described in the following paragraphs.
Do not use oxygen or air to build up pressure. Explosion hazard
can cause severe personal injury or death.
Evacuation
After determining the unit is tight and there are no refrigerant
leaks, evacuate the system. Use a vacuum pump with a
pumping capacity of approximately 3 cu.ft./min. and the
ability to reduce the vacuum in the unit to at least 1 mm (1000
microns).
Connect a mercury manometer or an electronic or other
1
type of micron gauge to the unit at a point remote from
the vacuum pump. For readings below 1 millimeter, use
an electronic or other micron gauge.
Use the triple evacuation method, which is particularly
2
helpful if the vacuum pump is unable to obtain the
desired 1 mm of vacuum. The system is first evacuated
to approximately 29" (740 mm) of mercury. Then add
enough refrigerant vapor to the system to bring the
pressure up to 0 pounds (0 microns).
Evacuate the system again to 29" (740 mm) of vacuum.
3
Repeat his procedure three times. This method is most
effective by holding system pressure at 0 pounds
(0 microns) for a minimum of 1 hour between
evacuations. The first pulldown removes about 90% of
the noncondensables; the second removes about 90% of
that remaining from the first pulldown. After the third
pulldown, only 1/10 of 1% of noncondensables remains.
Table 7, page 30
shows the relationship between pressure,
microns, atmospheres, and the boiling point of water.
Before replacing refrigerant sensors or protective devices, see
"Refrigerant Charge"‚ page 31
prevent an abrupt loss of the entire charge.
WARNING
CAUTION
for an important warning to
29
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