SERVICING
33
S-104 CHECKING COMPRESSOR EFFICIENCY
The reason for compressor inefficiency is broken or
damaged
scroll flanks on Scroll compressors, reducing the ability of
the compressor to pump refrigerant 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 dill
valves.
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, evacuate and recharge.
S-106 OVERFEEDING
Overfeeding by the expansion valve results in high suction
pressure, cold suction line, and possible liquid slugging of the
compressor.
If these symptoms are observed:
1. Check for an overcharged unit by referring to the cooling
performance charts in the spec sheet manual.
2. Check the operation of the power element in the valve.
3. Check for restricted or plugged equalizer tube.
S-108 SUPERHEAT
CHECKING SUPERHEAT
Refrigerant gas is considered superheated when its tem-
perature is higher than the saturation temperature corre-
sponding to its pressure. The degree of superheat equals the
degrees of temperature increase above the saturation tem-
perature 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
stabilize.
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) 65 70 75 80 85
100 --- --- --- 10 10
95 ------101010
90 ------121518
85 --- 10 13 17 20
80 --- 10 15 21 26
75 10 13 17 25 29
70 10 17 20 28 32
65 13 19 26 32 35
60 17 25 30 33 37
Return Air Temp. (°F Drybulb)
SYSTEM SUPERHEAT
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.
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