Carrier 38TN Service Manual page 14

DIAPHRAGM
INLET
pushrods and tends to close the valve. Therefore, bulb pressure
equals evaporator pressure (at outlet of coil) plus spring
pressure. If the load increases, the temperature increases at the
bulb, which increases the pressure on the topside of the
diaphragm, which pushes the pin carrier away from the seat,
opening the valve and increasing the flow of refrigerant. The
increased refrigerant flow causes increased leaving evaporator
pressure which is transferred via the equalizer tube to the
underside of the diaphragm. This tends to cause the pin carrier
spring pressure to close the valve. The refrigerant flow is
effectively stabilized to the load demand with negligible
change in superheat.
Step 7—Coil Removal
Coils are easy to remove if required for compressor removal, or to
replace coil. Shut off all power to unit. Remove and recover
refrigerant from system through service valves.
Wear safety glasses and gloves when handling refrigerants.
1. Remove top cover. (See Remove Top Cover in Cabinet
section of the manual.)
2. Remove screws in base pan to coil grille.
3. Remove coil grille from unit.
4. Remove screws on corner post holding coil tube sheet.
Cut tubing to reduce possibility of fire and personal injury.
5. Use midget tubing cutter to cut liquid and vapor lines at both
sides of coil. Cut in convenient location for easy reassembly
with copper slip couplings.
6. Lift coil vertically from basepan and place aside carefully.
7. Reverse procedure to reinstall coil.
PUSHRODS
FEEDER TUBES
OUTLET
NEEDLE
VALVE
SPRING
DISTRIBUTOR
Fig. 19—TXV Operation
CAPILLARY TUBE
COIL
EXTERNAL EQUALIZER TUBE
Step 8—Accumulator
Under some light load conditions on indoor coils, some liquid
refrigerant is present in suction gas returning to compressor. The
accumulator stores liquid and allows it to boil off into a vapor so
it can be safely returned to compressor. Since a compressor is
designed to pump refrigerant in its gaseous state, introduction of
liquid into it could cause severe damage or total failure of
compressor.
The accumulator is a passive device which seldom needs replac-
ing. Occasionally its internal oil return orifice or bleed hole may
become plugged. Some oil is contained in refrigerant returning to
compressor. It cannot boil off in accumulator with liquid refriger-
ant. The bleed hole allows a small amount of oil and refrigerant to
enter the return line where velocity of refrigerant returns it to
compressor. If bleed hole plugs, oil is trapped in accumulator, and
compressor will eventually fail from lack of lubrication. If bleed
hole is plugged, accumulator must be changed. Bleed hole is so
tiny that cleaning efforts usually are not successful. The accumu-
lator has a fusible element located in the bottom end bell. (See Fig.
20.) This fusible element will melt at 430° F and vent the
refrigerant if this temperature is reached either internal or external
to the system. If fuse melts, the accumulator must be replaced.
To change accumulator:
1. Shut off all power to unit.
2. Remove and reclaim all refrigerant from system.
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.
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BULB
A94056