Daikin DZ16 - S-106 OVERFEEDING; S-107 UNDERFEEDING; S-108 SUPERHEAT; SUPERHEAT AND SUBCOOLING ADJUSTMENT ON TXV APPLICATIONS

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SERVICING
S-106 OVERFEEDING
Overfeeding by the expansion valve results in high sucon
pressure, cold sucon 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 servicing secon.
2. Check the operaon of the power element in the valve as
explained in S-110 Checking Expansion Valve Operaon.
3. Check for restricted or plugged equalizer tube.
S-107 UNDERFEEDING
Underfeeding by the expansion valve results in low system ca-
pacity and low sucon pressures.
If these symptoms are observed:
1. Check for a restricted liquid line or drier. A restricon will be
indicated by a temperature drop across the drier.
2. Check the operaon of the power element of the valve as
described in S-110 Checking Expansion Valve Operaon.
S-108 SUPERHEAT
The expansion valves are factory adjusted to maintain 8 to
12 degrees superheat of the sucon gas. Before checking the
superheat or replacing the valve, perform all the procedures
outlined under Air Flow, Refrigerant Charge, Expansion Valve -
Overfeeding, Underfeeding. These are the most common causes
for evaporator malfuncon.
CHECKING SUPERHEAT
Refrigerant gas is considered superheated when its temperature
is higher than the saturaon temperature corresponding to its
pressure. The degree of superheat equals the degrees of tem-
perature increase above the saturaon temperature at exisng
pressure. See Temperature - Pressure Chart on following pages.
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. For best results, temporarily install a thermometer on the
liquid line at the liquid line service valve and 4-6” from the
compressor on the sucon line. Ensure the thermometer
makes adequate contact and is insulated for best possible
readings. Use liquid line temperature to determine sub-cool-
ing and vapor temperature to determine superheat.
NOTE: An oponal method is to locate the thermometer at the
sucon line service valve. Ensure the thermometer makes ade-
quate contact and is insulated for best possible readings.
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.
EXAMPLE:
a. Sucon Pressure = 143
b. Corresponding Temp. °F. = 50
c. Thermometer on Sucon Line = 61°F.
To obtain the degrees temperature of superheat, subtract 50.0
from 61.0°F.
The dierence is 11° Superheat. The 11° Superheat would fall in
the ± range of allowable superheat.
SUPERHEAT AND SUBCOOLING ADJUSTMENT ON TXV APPLICA-
TIONS
NOTE: Units mached with indoor coils equipped with nonadjust-
able TXV should be charged by subcooling only.
1. Run system at least 10 minutes to allow pressure to stabilize.
2. For best results, temporarily install a thermometer on the
liquid line at the liquid line service valve and 4-6” from the
compressor on the sucon line. Ensure the thermometer
makes adequate contact and is insulated for best possible
readings. Use liquid line temperature to determine sub-cool-
ing and vapor temperature to determine superheat.
NOTE: An oponal method is to locate the thermometer
at the sucon line service valve. Ensure the thermometer
makes adequate contact and is insulated for best possible
readings.
3. Check subcooling and superheat. Systems with TXV applica-
on should have a subcooling of 7 to 9 ºF and superheat of 7
to 9 ºF.
a. If subcooling and superheat are low, adjust TXV to 7 to
9 ºF superheat, then check subcooling.
NOTE: To adjust superheat, turn the valve stem clockwise to
increase and counter clockwise to decrease.
b. If subcooling is low and superheat is high, add charge
to raise subcooling to 7 to 9 ºF then check superheat.
c. If subcooling and superheat are high, adjust TXV valve
to 7 to 9 ºF superheat, then check subcooling.
d. If subcooling is high and superheat is low, adjust TXV
valve to 7 to 9 ºF superheat and remove charge to lower the
subcooling to 7 to 9 ºF.
The TXV should NOT be adjusted at light load condions 55º
to 60ºF, under such condions only the subcooling can be
evaluated. This is because sucon pressure is dependent on
the indoor coil match, indoor airow, and wet bulb tempera-
ture. NOTE: Do NOT adjust charge based on sucon pressure
unless there is a gross undercharge.