Condensing Unit & Heat Pump R410A Service Manual

118
SERVICING
necessary.
1. Purge gauge lines. Connect service gauge manifold to base-
valve service ports. Run the system in low stage at least 10
minutes to allow pressure to stabilize.
2. 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 subcooling and vapor tem-
perature to determine superheat.
3. Check subcooling and superheat. Systems with TXV applica-
on should have a subcooling of 5 to 7°F and superheat of 7
to 9 °F.
a. If subcooling and superheat are low, adjust TXV to 7 to
9 ºF superheat, and 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 5 to 7 °F 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 5 to 7 ºF.
NOTE: Do NOT adjust the charge based on sucon pressure
unless there is a gross undercharge.
4. Disconnect manifold set, installaon is complete.
SUBCOOLING FORMULA = SATURATED LIQUID TEMP. - LIQUID
LINE TEMP.
NOTE: Check the Schrader ports for leaks and ghten valve cores
if necessary. Install caps nger-ght.
HEAT PUMP - HEATING CYCLE
The proper method of charging a heat pump in the heat mode
is by weight with the addional charge adjustments for line size,
line length, and other system components. For best results on
outdoor units with TXVs, superheat should be 2-5°F at 4-6” from
the compressor. Make nal charge adjustments in the cooling
cycle.
S-104 CHECKING COMPRESSOR EFFiCIENCY
The reason for compressor ineciency is broken or damaged
scroll anks on Scroll compressors, reducing the ability of the
compressor to pump refrigerant vapor.
The condion of the scroll anks is checked in the following
manner.
1. Aach 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 dierence 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 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
capacity 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 7 to 9
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 temperature increase above the saturaon temperature
at exisng pressure. See Temperature - Pressure Chart on
following pages.