Service Manual

SERVICING
34
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 refrig-
erant vapor.
The condition of the valves or scroll flanks is checked in the fol-
lowing manner.
1. Attach gauges to the high and low side of the system.
2. St art the syst em and run a Cooling Performance Test .
If the t est show s-
⇒ 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 COM PRESSOR 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 refrig-
erant vapor.
During t he " OFF" cycle, t he high side pressure bleeds t o the low
side through the fixed orifice rest riction device. Check equaliza-
tion time as follows:
1. Attach a gauge manifold to the suction and liquid line access
fit tings.
2. St art the syst em and allow the pressures t o st abilize.
3. St op the system and check t he t ime it takes for the high and
low pressure gauge readings to equalize.
If it takes more than seven (7) minutes to equalize, the rest rictor
device is inoperat ive. Replace, install a liquid line drier, evacuat e
and recharge.
S-108 SUPERHEAT
CHECKING SUPERHEAT
Refrigerant gas is considered superheat ed whenever its tempera-
ture is higher than the sat uration temperature corresponding to
its pressure. The degree of superheat equals the degrees of tem-
perature increase above the sat urat ion temperature 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 st abi-
lize.
2. Temporarily install t hermomet er on suct ion (large) line near
compressor wit h adequate contact and insulate for best
possible reading.
3. Refer to the superheat table provided for proper syst em su-
perheat . Add charge to lower superheat or recover charge to
raise superheat .
Superheat Formula = Suct. Line Tem p. - Sat. Suct. Temp.
100 - - - 10 10
95 - - 10 10 10
90 - - 12 15 18
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
Ambient Condenser
Inlet Temp (°F
Drybulb)
65 70 75
Return Air Temp. (°F Drybulb)
80 85
EXAMPLE:
a. Suction Pressure = 143
b. Corresponding Temp. °F. = 50
c. Thermometer on Suction Line = 59°F.
To obtain the degrees temperature of superheat , subt ract 50.0
from 59.0°F.
The difference is 9° Superheat . The 9° Superheat would fall in
the ± range of allow able superheat .
S-109 CHECKING SUBCOOLING
Refrigerant liquid is considered subcooled when its temperature
is lower than the saturat ion temperature corresponding t o its
pressure. The degree of subcooling equals the degrees of tem-
perature decrease below the saturat ion temperature at the ex-
ist ing pressure.
1. Att ach an accurate thermometer or preferably a thermo-
couple type temperature tester to the liquid line close to the
pressure switch.
2. Install a high side pressure gauge on the liquid access fitt ing.
3. Record the gauge pressure and the temperature of the line.
4. Compare t he hi-pressure reading to the "Required Liquid Line
Temperature" chart. Find the hi-pressure value on the left
column. Follow that line right to the column under the de-
sign subcooling value. Where t he t wo int ersect is the required
liquid line temperature.
Alternately you can convert the liquid line pressure gauge
reading to temperature by finding the gauge reading in Tem-
perature - Pressure Chart and reading to the left , find the tem-
perature in the °F. Column.
5. The difference between the thermometer reading and pressure
to t emperat ure conversion is the amount of subcooling.