Installation manual

ManualsBrandsMcQuay ManualsPrint & ScanRDS 802C

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Piping recommendations

1. Use type K or L clean copper tubing. All joints should be

thoroughly cleaned or brazed with high temperature solder.

2. Piping sizes should be based 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.

3. Suction line piping pressure drop should not exceed the

pressure equivalent of 2°F (1°C), 3 psi (20.7 kPa) per 100

feet (30.5 m) of equivalent pipe length. After the suction

line size has been determined, the vertical suction risers

should be checked to verify that oil will be carried up the

riser and back to the compressor. The suction line(s)

should be pitched in the direction of refrigerant flow and

adequately supported. Lines should be free draining and

fully insulated between the evaporator and the compressor.

4. Vertical suction risers should be checked using Table 4 to

determine the minimum tonnage required to carry oil up

suction risers of various sizes.

5. The liquid line should be sized for a pressure drop not to

exceed the pressure equivalent of 2°F (1°C), 6 psi (41.4

kPa) saturated temperature. The RDS unit includes a

factory installed filter-drier, solenoid valve, and sightglass

in each liquid line, upstream of the thermostatic expan-

sion valve.

Table 4. Minimum tonnage (R-22) to carry oil up suction

riser at 40

F saturated suction

LINE SIZE

O.D.

⁄8"1

⁄8"2

⁄8"3

⁄8"4

⁄8"

MINIMUM

TONS

1.50 2.50 3.80 7.60 13.10 20.4 29.7 41.3

Note: When compressor minimum tonnage is less than shown in the above

table for a given line size, double suction risers will be required.

Leak testing

The field piping system should be checked for leaks prior to

charging. Leak testing must be performed to current EPA

standards and regulations. After making any necessary re-

pair, the system should be evacuated as described in the

following paragraphs.

Do not use oxygen to build up pressure.

A serious explosion could result from using oxygen to

build up pressure, resulting in severe personal injury or

death.

Evacuation

After it has been determined that the unit is tight and there are

no refrigerant leaks, the system should be evacuated. The

use of a vacuum pump with a pumping capacity of approxi-

mately 3 cu.ft./min. and the ability to reduce the vacuum in

the unit to at least 1 millimeter (1000 microns) is recom-

mended.

1. A mercury manometer or an electronic or other type of

micron gauge should be connected to the unit at a point

remote from the vacuum pump. For readings below 1

millimeter, an electronic or other micron gauge should be

used.

2. The triple evacuation method is recommended and is

particularly helpful if the vacuum pump is unable to obtain

the desired 1 millimeter of vacuum. The system is first

evacuated to approximately 29" (740 mm) of mercury.

Enough refrigerant vapor is then added to the system to

bring the pressure up to 0 pounds (0 microns).

3. Then the system is once again evacuated to 29" (740 mm)

of vacuum. This procedure is repeated three times. This

method can be most effective by holding system pressure

at 0 pounds (0 microns) for a minimum of 1 hour between

evacuations. The first pulldown will remove about 90% of

the noncondensables, the second about 90% of that

remaining from the first pulldown, after the third, only 1/10

of 1% of noncondensables will remain.

Table 5 below shows the relationship between pressure,

microns, atmospheres, and the boiling point of water.

Table 5. Pressure-vacuum equivalents

ABSOLUTE PRESSURE ABOVE ZERO VACUUM BELOW 1 ATMOSPHERE

APPROXIMATE BOILING POINT

MERCURY MERCURY

FRACTION OF OF H

O AT EACH

MICRONS PSIA

(MM) (IN.)

1 ATMOSPHERE PRESSURE (

°F)

0 0 760.00 29.921 — —

50 0.001 759.95 29.920 1/15,200 –50

100 0.002 759.90 29.920 1/7,600 –40

150 0.003 759.85 29.920 1/5,100 –33

200 0.004 759.80 29.910 1/3,800 –28

300 0.006 759.70 29.910 1/2,500 –21

500 0.009 759.50 29.900 1/1,520 –12

1,000 0.019 759.00 29.880 1/760 1

2,000 0.039 758.00 29.840 1/380 15

4,000 0.078 756.00 29.760 1/189 29

6,000 0.117 754.00 29.690 1/127 39

8,000 0.156 752.00 29.600 1/95 46

10,000 0.193 750.00 29.530 1/76 52

15,000 0.290 745.00 29.330 1/50 63

20,000 0.387 740.00 29.130 1/38 72

30,000 0.580 730.00 28.740 1/25 84

50,000 0.967 710.00 27.950 1/15 101

100,000 1.930 660.00 25.980 2/15 125

200,000 3.870 560.00 22.050 1/4 152

500,000 9.670 260.00 10.240 2/3 192

760,000 14.697 0 0 1 Atmosphere 212

WARNING