S-106 Overfeeding; S-107 Underfeeding; S-108 Superheat; S-109 Checking Subcooling - Daikin DP14UM Service Instructions Manual

SERVICING
The bulb must be securely fastened to a clean straight
section of the suction line. Application of the bulb to a
horizontal run of line is preferred. If a vertical installation
cannot be avoided the bulb should be mounted so that the
capillary tubing comes out at the top.
THE VALVES PROVIDED ARE DESIGNED TO MEET THE
SPECIFICATION REQUIREMENTS FOR OPTIMUM PRODUCT
OPERATION. DO NOT USE SUBSTITUTES.

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 servicing section.
2. Check the operation of the power element in the
valve as explained in Checking Expansion Valve
Operation.
3. Check for restricted or plugged equalizer tube.

S-107 Underfeeding

Underfeeding by the expansion valve results in low system
capacity and low suction pressures.
If these symptoms are observed:
1. Check for a restricted liquid line or drier. A restriction
will be indicated by a temperature drop across the
drier.
2. Check the operation of the power element of the
valve as described in Checking Expansion Valve
Operation.

S-108 Superheat

The expansion valves are factory adjusted to maintain
12 to 15 degrees superheat of the suction 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
malfunction.
Checking Superheat
Refrigerant gas is considered superheated when its
temperature 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 on following page.
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.
EXAMPLE:
A. Suction Pressure = 143
B. Corresponding Temp. °F. = 50
C. Thermometer on Suction Line = 61°F.
To obtain the degrees temperature of superheat, subtract
50.0 from 61.0°F.
The difference is 11° Superheat. The 11° Superheat would
fall in the ± range of allowable superheat.
Superheat And Subcooling Adjustment
On Txv Applications
1. Run system at least 10 minutes to allow pressure to
stabilize.
2. Temporarily install thermometer on liquid (small) line
near pressure switches with adequate contact and
insulate for best possible reading.
3. Check subcooling and superheat. Systems with TXV
application should have a subcooling and superheat
of 12 - 15 ºF.
A. If subcooling and superheat are low, adjust TXV
to 9 ± 3ºF then check subcooling.
B. If subcooling is low and superheat is high, add
charge to raise subcooling to 10ºF then check
superheat.
C. If subcooling and superheat are high, adjust TXV
valve to 12 - 15 ºF then check subcooling.
If subcooling is high and superheat is low, adjust
TXV valve to 12 - 15 ºF superheat and remove
charge to lower the subcooling to 2 - 15 ºF.
CAUTION
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