Contaminant Removal; System Charging; Checking Charge - Carrier R-22 Application Manual And Service Manual

NOTE: Coil may be removed for access to accumulator. Refer to
appropriate sections of service manual for instructions.
Wear safety glasses and gloves when working on refrigerants
and when using brazing torch.
3. When accumulator is exposed, remove it from system with
tubing cutter.
4. Scratch matching marks on tubing stubs and old accumulator.
Scratch matching marks on new accumulator. Unbraze stubs
from old accumulator and braze into new accumulator.
5. Thoroughly rinse any flux residue from joints and paint with
corrosion-resistant coating such as zinc-rich paint.
6. Reinstall accumulator into system with copper-slip couplings.
7. Evacuate and charge system.
8. Pour and measure oil quantity (if any) from old accumulator.
If more than 20 percent of oil charge is trapped in accumula-
tor, add oil to compressor to make up for this loss.
Fig. 53—Accumulator
Step 12—Contaminant Removal
Proper evacuation of a unit removes non-condensibles and assures
a tight, dry system before charging. The 2 methods used to
evacuate a system are the deep-vacuum method and the triple-
evacuation method.
DEEP-VACUUM METHOD
The deep-vacuum method requires a vacuum pump capable of
pulling a vacuum of 1000 microns and a vacuum gage capable of
accurately measuring this vacuum depth. The deep-vacuum
method is the most positive way of assuring a system is free of air
and liquid water.
TRIPLE-EVACUATION METHOD
The triple-evacuation method can be used where the vacuum pump
is capable of pumping down to only 28 in. of mercury vacuum, and
the system does not contain any liquid water. The procedure is as
follows.
1. Pump the system down to 28 in. of mercury vacuum and allow
pump to continue to operate for additional 15 minutes.
2. Close service valves and shut off vacuum pump.
3. Connect a refrigerant cylinder to the system and open until
system pressure is 2 psig.
430 FUSE
ELEMENT
A88410
4. Close the service valve.
5. Allow system to stand for 1 hr, during which time the dry
refrigerant will be able to diffuse throughout the system,
absorbing moisture.
This procedure is repeated 3 times, after which the system will be
free of any contaminants and water vapor.
Step 13—System Charging
For all approved combinations, system must be charged correctly
for normal system operation and reliable operation of components.
Always wear safety glasses and gloves when handling refrig-
erants.
If system has lost all charge, weigh in charge using dial-a-charge
or digital scale.
System charge should be fine-tuned by using the superheat or
subcooling method, whichever is appropriate. These methods are
covered in the Checking Charge section below.
NOTE: Heat-pump check charts are for checking charge and
performance and for adding a small amount of charge. During
heating mode, correct method of charging is the weight method. In
heating mode, check should be made approximately 15 minutes
after a defrost with unit running with a clean coil. In cooling cycle,
system should run at least 10 minutes for temperatures and
pressures to stabilize. All charts assume there are no system
abnormalities and indoor coil airflows are correct. If system
abnormalities exist, correct them before checking system charge.
Step 14—Checking Charge
Superheat charging is the process of charging refrigerant into a
system until the temperature (superheat) of the suction gas entering
the compressor reaches a prescribed value. Small variations of
charge affect suction-gas superheat temperatures greatly. There-
fore, this method of charging is very accurate. This method can be
used only on split-system condensing units and heat pumps
(operating in the cooling mode) with fixed-restrictor-type metering
devices such as AccuRater™, cap tube, and so forth. For units
using a TXV, the subcooling method must be used. Heat pumps
must be operating in the cooling mode. To charge by superheat, a
service technician needs an accurate superheat thermocouple or
thermistor-type thermometer, a sling psychrometer, and a gage
manifold. Do not use mercury or small-dial-type thermometers as
they are not adequate for this type of measurement. Then use one
of the following procedures:
SUPERHEAT CHARGING METHOD
1. Operate a unit a minimum of 10 minutes before checking
charge.
2. Measure vapor pressure by attaching a gage to vapor valve-
service port.
3. Measure vapor-line temperature by attaching a service ther-
mometer to unit vapor line near vapor valve. On a heat pump,
attach to the suction tube between the accumulator and the
compressor. Insulate thermometer for accurate readings.
4. Measure outdoor-air, dry-bulb temperature with a second
thermometer.
5. Measure indoor-air (entering indoor coil), wet-bulb tempera-
ture with a sling psychrometer.
6. Locate outdoor temperature and evaporator entering air wet-
bulb temperature in Table 22. At this intersection note the
superheat.
45