GSZH5 Service Manual
98
SERVICING
for best possible readings. Use liquid line temperature
to determine subcooling and vapor temperature to
determine superheat.
3. Check subcooling and superheat. Systems with TXV
application should have a subcooling of 5 to 7°F and
superheat of 7 to 9°F.
decrease.
4. If subcooling and superheat are low, adjust TXV to 7 to
9ºF superheat, and then check subcooling.
5. If subcooling is low and superheat is high, add charge
to raise subcooling to 5 to 7°F then check superheat.
6. If subcooling and superheat are high, adjust TXV valve
to 7 to 9ºF superheat, then check subcooling.
7. If subcooling is high and superheat is low, adjust TXV
valve to 7 to 9ºF superheat and remove charge to lower
the subcooling to 5 to 7ºF.
pressure unless there is a gross undercharge.
8. Disconnect manifold set, installation is complete.
SUBCOOLING FORMULA = SATURATED LIQUID TEMP.
- LIQUID LINE TEMP.
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
charge adjustments in the cooling cycle.
ability of the compressor to pump refrigerant vapor.
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
d. Low amp draw at compressor.
And the charge is correct. The compressor is faulty -
replace the compressor.
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.
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.
1. Purge gauge lines. Connect service gauge manifold
to base-valve service ports. Run system at least 10
minutes to allow pressure to stabilize.
2. Temporarily install a thermometer 4-6” from
the compressor on the suction line. Ensure the
thermometer makes adequate contact and is insulated
for best possible readings. Use vapor temperature to
determine superheat.
3. Refer to the superheat table provided for proper system
superheat. Add charge to lower superheat or recover
charge to raise superheat.
4. Disconnect manifold set, installation is complete.
SUPERHEAT FORMULA = SUCT. LINE TEMP. - SAT.
SUCT. TEMP.