GSX14 Service Manual

SERVICING
159
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. Check subcooling and superheat. Systems with TXV
application 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 subcool-
ing.
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.
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 = Sat. Liquid Temp. - Liquid Line Temp.
S-110 CHECKING EXPANSION VALVE OPERA-
TION
1. Remove the remote bulb of the expansion valve from the
suction line.
2. Start the system and cool the bulb in a container of ice
water, closing the valve. As you cool the bulb, the suction
pressure should fall and the suction temperature will rise.
3. Next warm the bulb in your hand. As you warm the bulb,
the suction pressure should rise and the suction tempera-
ture will fall.
4. If a temperature or pressure change is noticed, the
expansion valve is operating. If no change is noticed, the
valve is restricted, the power element is faulty, or the
equalizer tube is plugged.
5. Capture the charge, replace the valve and drier, evacuate
and recharge.
S-111 FIXED ORIFICE RESTRICTOR DEVICES
The fixed orifice restrictor device (flowrator) used in conjunc-
tion with the indoor coil is a predetermined bore (I.D.).
It is designed to control the rate of liquid refrigerant flow into
an evaporator coil.
The amount of refrigerant that flows through the fixed orifice
restrictor device is regulated by the pressure difference
between the high and low sides of the system.
In the cooling cycle when the outdoor air temperature rises,
the high side condensing pressure rises. At the same time,
the cooling load on the indoor coil increases, causing the low
side pressure to rise, but at a slower rate.
Since the high side pressure rises faster when the tempera-
ture increases, more refrigerant flows to the evaporator,
increasing the cooling capacity of the system.
When the outdoor temperature falls, the reverse takes place.
The condensing pressure falls, and the cooling loads on the
indoor coil decreases, causing less refrigerant flow.
A strainer is placed on the entering side of the tube to prevent
any foreign material from becoming lodged inside the fixed
orifice restriction device.
If a restriction should become evident, proceed as follows:
1. Recover refrigerant charge.
2. Remove the orifice or tube strainer assembly and re-
place.
3. Replace liquid line drier, evacuate and recharge.
CHECKING EQUALIZATION TIME
During the "OFF" cycle, the high side pressure bleeds to the
low side through the fixed orifice restriction device. Check
equalization time as follows:
1. Attach a gauge manifold to the suction and liquid line dill
valves.
2. Start the system and allow the pressures to stabilize.
3. Stop the system and check the time it takes for the high
and low pressure gauge readings to equalize.
If it takes more than seven (7) minutes to equalize, the
restrictor device is inoperative. Replace, install a liquid line
drier, evacuate and recharge.
S-112 CHECKING RESTRICTED LIQUID LINE
When the system is operating, the liquid line is warm to the
touch. If the liquid line is restricted, a definite temperature
drop will be noticed at the point of restriction. In severe
cases, frost will form at the restriction and extend down the
line in the direction of the flow.
Discharge and suction pressures will be low, giving the
appearance of an undercharged unit. However, the unit will
have normal to high subcooling.
Locate the restriction, replace the restricted part, replace
drier, evacuate and recharge.
S-113 OVERCHARGE OF REFRIGERANT
An overcharge of refrigerant is normally indicated by an
excessively high head pressure.
An evaporator coil, using an expansion valve metering device,
will basically modulate and control a flooded evaporator and
prevent liquid return to the compressor.
An evaporator coil, using a capillary tube metering device,
could allow refrigerant to return to the compressor under
extreme overcharge conditions. Also with a capillary tube
metering device, extreme cases of insufficient indoor air can
cause icing of the indoor coil and liquid return to the
compressor, but the head pressure would be lower.