Step 8—Metering device
Refrigerant metering devices are fixed orifices and are located in
the inlet header to the indoor and outdoor coils.
Step 9—Liquid line strainers
The liquid line strainers (to protect metering devices) are made of
wire mesh and are located in the liquid lines on the inlet side of the
metering devices.
Step 10—High Flow Valves
High flow valves are located on the compressor hot gas and
suction tubes. Large black plastic caps distinguish these valves
with O-rings located inside the caps. These valves can not be
accessed for service in the field. Ensure the plastic caps are in
place and tight or the possibility of refrigerant leakage could occur.
Step 11—Time-delay relay
The Time-Delay Relay (TDR) is a solid-state control, recycle
delay timer which keeps indoor blower operating for 60 sec. after
thermostat is satisfied. This delay enables blower to remove
residual cooling in coil after compression shutdown, thereby
improving efficiency of system. The sequence of operation is that
on closure of wall thermostat and at end of a fixed on delay of 1
sec., fan relay is energized. When thermostat is satisfied, an off
delay is initiated. When fixed delay of 60± 5 sec. is completed, fan
relay is de-energized and fan motor stops. If wall thermostat closes
during this delay, TDR is reset and fan relay remains energized.
TDR is a 24-v device that operates within a range of 15-v to 30-v
and draws about 0.5 amps. If the blower runs continuously instead
of cycling off when the fan switch is set on AUTO, the TDR is
probably defective and must be replaced.
Step 12—Loss of charge switch
The loss of charge switch is located on the outdoor liquid line. This
switch contains a Schrader core depressor. This switch opens at 7
psig and closes at 22 psig. No adjustment is necessary.
NOTE: Because these switches are attached to refrigeration
system under pressure, it is not advisable to remove this device for
troubleshooting unless you are reasonably certain that a problem
exists. If switch must be removed, remove and recover all system
charge so that pressure gages read 0 psi. Never open system
without breaking vacuum with dry nitrogen.
Step 13—Check defrost thermostat
There is a liquid header with a brass distributor and feeder tube
going into outdoor coil. At the end of 1 of the feeder tubes, there
is a 3/8-in. OD stub tube approximately 3 in. long (See Fig. 24).
The defrost thermostat should be located on this stub tube. Note
that there is only 1 stub tube used with liquid header, and on most
units it is the bottom circuit.
Step 14—Defrost Thermostat
Defrost thermostat signals heat pump that conditions are right for
defrost or that conditions have changed to terminate defrost. It is
a thermally actuated switch clamped to outdoor coil to sense its
temperature. Normal temperature range is closed at 30° +/- 3°F
and open at 80° +/- 5°F.
NOTE: The defrost thermostat must be located on the liquid side
of the outdoor coil on the bottom circuit and as close to the coil as
possible.
TROUBLESHOOTING
Refer to the Cooling and Heating Troubleshooting Chart (Table 9)
for troubleshooting information.
START-UP CHECKLIST
Use the Start-Up Checklist to ensure proper start-up procedures are
followed.
Fig. 21—Defrost Thermostat
C99029
FEEDER TUBE
STUB TUBE
DEFROST
THERMOSTAT
C99097
Fig. 20—Refrigerant Circuit
18
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