15
4. Clean coil using a commercial coil cleaner or dish-
washer detergent in a pressurized spray canister. Wash
both sides of coil and flush with clean water. For best
results, back --flush toward return--air section to re-
move foreign material. Flush condensate pan after
completion.
5. Reinstall economizer and filters.
6. Reconnect wiring.
7. Replace access panels.
THERMOSTATIC EXPANSION
VALVE (TXV)
All 48HC’s have a factory installed nonadjustable
thermostatic expansion valve (TXV). The TXV will be a
bi-flow, bleed port expansion valve with an external
equalizer. TXVs are specifically designed to operate with
PuronR or R-22 refrigerant, use only factory authorized
TXVs. Do not interchange Puron and R-22 TXVs.
TXV Operation
The TXV is a metering device that is used in air
conditioning and heat pump systems to adjust to the
changing load conditions by maintaining a preset
superheat temperature at the outlet of the evaporator coil.
See Fig. 20.
The volume of refri gerant metered through the valve seat
is dependent upon the following:
1. Superheat temperature is sensed by cap tube sensing
bulb on suction tube at outlet of evaporator coil. T his
temperature i s converted into pressure by refrigerant
in the bulb pushing downward on the diaphragm
which opens the val ve using the push rods.
2. The suction pressure at the outlet of the evaporat or
coil is transferred through the external equalizer tube
to the underside of the diaphragm.
3. The pin is spring loaded, which exerts pressure on the
underside of the diaphragm. The r efore, the bulb pres-
sure works against the spring pressure and evaporator
suction pressure to open the valve. If the load in-
creases, the temperature increases at the bulb, which
increases the pressure on the top side of the dia-
phragm. This opens the valve and increases the flow
of refrige rant. The increased refrigera nt flow causes
the leaving evaporator temperature to decrease. This
lowers the pressure on the diaphragm and closes the
pin. The refrigerant flow is effectively stabilized to
the load demand with negligible change in superheat.
Replacing TXV
1. Recover refrigerant.
2. Remove TXV support clamp using a 5/l6-in. nut
driver.
3. Remove TXV using a wrench and an additional
wrench on connections to prevent damage to tubing.
4. Remove equalizer tube from suction line of coil. Use
file or tubing cutter to cut brazed equalizer line
approximately 2 inches above suction tube.
5. Remove bulb from vapor tube inside cabinet.
6. Install the new TXV using a wrench and an additional
wrench on connections to prevent damage to tubing
while attaching TXV to distributor.
7. Attach the equalizer tube to the suction line. If the
coil has mechanical a connection, then use a wrench
and an additional wrench on connections to prevent
damage. If the coil has a brazed connection, use a file
or a tubing cutter to remove the mechanical flare nut
from the equalizer line. Then use a new coupling to
braze the equaliz er line to the stub (pre vious equalizer
line) in suction line.
8. Attach TXV bulb in the same location where the ori-
ginal (in the sensing bulb indent) was when it was re-
moved, using t he supplied bulb clamps. See Fig. 19.
TXV SENSING
BULB
CLAMP
THERMAL EXPANSION
(TXV) VALVE
SENSING BULB INSULATION REMOVED FOR CLARITY
C10372
Fig. 19 -- TXV Valve and Sensing Bulb Location
9. Route equalizer tube through suct ion connection
opening (large hole) in fitting panel and install fitting
panel in place.
10. Sweat the inlet of TXV marked “IN” to the liquid
line. Avoid excessive heat which could damage the
TXV valve.
48HC
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