94
SERVICING
NOTE:
Do NOT adjust the charge based on suction pressure
unless there is a gross undercharge.
4. Disconnect manifold set, installation is complete.
SUBCOOLING FORMULA = SATURATED LIQUID TEMP. - LIQUID
LINE TEMP.
NOTE:
Check the Schrader ports for leaks and tighten valve cores
if necessary. Install caps finger-tight.
HEAT PUMP - HEATING CYCLE
The proper method of charging a heat pump in the heat mode
is by weight with the additional charge adjustments for line size,
line length, and other system components. For best results on
outdoor units with TXVs, superheat should be 8°F at 4-6” from
the compressor. Make final charge adjustments in the cooling
cycle.
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.
The condition of the 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:
A. Below normal high side pressure.
B. Above normal low side pressure.
C. Low temperature difference across coil.
D. Low amp draw at compressor.
And the charge is correct. The compressor is faulty - replace the
compressor.
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 S-110 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 S-110 Checking Expansion Valve Operation.
S-108 SUPERHEAT
The expansion valves are factory adjusted to maintain 7 to
9 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
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 suction line. Ensure the thermometer
makes adequate contact and is insulated for best possible
readings. Use liquid line temperature to determine sub-
cooling and vapor temperature to determine superheat.
NOTE:
An optional method is to locate the thermometer
at the suction line service valve. Ensure the thermometer
makes adequate 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.
