Checking Compressor Efficiency; Overfeeding; Checking Superheat - Daikin DCG Series Service Instructions Manual

SERVICING
After system has stabilized per startup instructions, com-
pare the operating pressures and outdoor unit amp draw to
the numbers listed in the spec sheet manual. If pressures
and amp draw are too low, add charge. If pressures and amp
draw are too high, remove charge. Check subcooling and
superheat as detailed in the following section.
5. With the system still running, remove hose and reinstall
both valve caps.
6. Check system for leaks.
Due to their design, Scroll compressors are inherently more
tolerant of liquid refrigerant.
NOTE: Even though the compressor section of a Scroll
compressor is more tolerant of liquid refrigerant, continued
floodback or flooded start conditions may wash oil from the
bearing surfaces causing premature bearing failure.S-104

CHECKING COMPRESSOR EFFICIENCY

The reason for compressor inefficiency is broken or damaged
suction and/or discharge valves, or scroll flanks on Scroll
compressors, reducing the ability of the compressor to pump
refrigerant 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
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 as
explained in S-110 Checking Expansion Valve Operation.
3. Check for restricted or plugged equalizer tube.
S-108 SUPERHEAT

CHECKING SUPERHEAT

Refrigerant gas is considered superheated when its tempera-
ture is higher than the saturation temperature corresponding
to its pressure. The degree of superheat equals the degrees
of temperature increase above the saturation 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
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
100 ---
95 ---
90 ---
85 ---
80 ---
75 10
70 10
65 13
60 17
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.
Return Air Temp. (°F Drybulb)
70 75 80 85
--- --- 10 10
--- 10 10 10
--- 12 15 18
10 13 17 20
10 15 21 26
13 17 25 29
17 20 28 32
19 26 32 35
25 30 33 37
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