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SERVICING
NOTE: Even though the compressor section of a Scroll com-
pressor is more tolerant of liquid refrigerant, continued flood-
back or flooded start conditions may wash oil from the bearing
surfaces causing premature bearing failure. S-104 CHECK-
ING COMPRESSOR EFFICIENCY
The reason for compressor inefficiency is broken or damaged
suction and/or discharge valves, or scroll flanks on Scroll com-
pressors, reducing the ability of the compressor to pump re-
frigerant vapor.
The condition of the valves or scroll flanks is checked in the
following manner.
1. Attach gauges to the high and low side of the system.
2. Start the system and run a Cooling Performance Test.
If the test shows-
⇒
Below normal high side pressure.
⇒
Above normal low side pressure.
⇒
Low temperature difference across coil.
⇒
Low amp draw at compressor.
-and the charge is correct. The compressor is faulty - replace
the compressor.
S-104 CHECKING COMPRESSOR
EFFICIENCY
The reason for compressor inefficiency is broken or damaged
suction and/or discharge valves, or scroll flanks on Scroll com-
pressors, reducing the ability of the compressor to pump re-
frigerant vapor.
During the "OFF" cycle, the high side pressure bleeds to the
low side through the fixed orifice restriction device. Check
equalization time as follows:
1. Attach a gauge manifold to the suction and liquid line ac-
cess fittings.
2. Start the system and allow the pressures to stabilize.
3. Stop the system and check the time it takes for the high
and low pressure gauge readings to equalize.
If it takes more than seven (7) minutes to equalize, the restrictor
device is inoperative. Replace, install a liquid line drier, evacu-
ate and recharge.
S-108 SUPERHEAT
CHECKING SUPERHEAT
Refrigerant gas is considered superheated whenever its tem-
perature is higher than the saturation temperature correspond-
ing to its pressure. The degree of superheat equals the de-
grees of temperature increase above the saturation tempera-
ture at existing pressure. See Temperature - Pressure Chart.
CAUTION
To prevent personal injury, carefully connect and
disconnect manifold gauge hoses. Escaping liquid
refrigerant can cause burns. Do not vent refrigerant
to atmosphere. Recover during system repair
or final unit disposal.
1. Run system at least 10 minutes to allow pressure to sta-
bilize.
2. Temporarily install thermometer on suction (large) line
near compressor with adequate contact and insulate for
best possible reading.
3. Refer to the superheat table provided for proper system
superheat. Add charge to lower superheat or recover
charge to raise superheat.
Superheat Formula = Suct. Line Temp. - Sat. Suct. Temp.
Ambient Condenser
Inlet Temp (°F
Drybulb)
100
95
90
85
80
75
70
65
60
EXAMPLE:
a. Suction Pressure = 143
b. Corresponding Temp. °F. = 50
c. Thermometer on Suction Line = 59°F.
To obtain the degrees temperature of superheat, subtract 50.0
from 59.0°F.
The difference is 9° Superheat. The 9° Superheat would fall in
the ± range of allowable superheat.
S-109 CHECKING SUBCOOLING
Refrigerant liquid is considered subcooled when its tempera-
ture is lower than the saturation temperature corresponding to
its pressure. The degree of subcooling equals the degrees of
temperature decrease below the saturation temperature at the
existing pressure.
1. Attach an accurate thermometer or preferably a thermo-
couple type temperature tester to the liquid line close to
the pressure switch.
Return Air Temp. (°F Drybulb)
65
70
75
80
-
-
-
10
-
-
10
10
-
-
12
15
-
10
13
17
-
10
15
21
10
13
17
25
10
17
20
28
13
19
26
32
17
25
30
33
85
10
10
18
20
26
29
32
35
37
35
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