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TM 5-4120-270-15
mation of condensation on the inside walls of the tubing.
Plug or cap all openings as a part is removed to
minimize the entry of dirt and moisture.
d. Use a silver solder on all soldered connections.
Easy-Flo silver solder (or equivalent) with a 50 percent
silver capacity and a melting point of approximately
1160°F is recommended. Continually pass dry nitrogen
through the tubing or connections being soldered to
prevent formation of harmful copper oxides.
e. After assembly of any flanged joint, apply one coat
of Amer-coat No. 40 to the joint.
f. After assembly of piping, coat all copper to-
aluminum joints with 3 coats Amer-coat No. 40 for a
distance of one inch on each side of joint as well as the
joint.
Note. Amer-coat may be force dried at a
maximum temperature of 140°F.
g. When removing and installing the solenoid valves,
direct flame away from the valve body to protect it from
heat damage. Keep the flame on the outside of the
distributor when disassembling or reassembling the
expansion valve.
h. No metal to metal contact is allowable on capillary
tubes; use tape to prevent such contact.
6-17. Thermal Expansion Valves
a. General. A 4 1/2-ton thermal expansion valve
controls the rate of flow of liquid refrigerant into the
evaporator coil during the cooling cycle of operation.
The 2.1 ton thermal expansion valve functions when the
unit is in the bypass cycle of operation. Each expansion
valve is provided with a superheat setting or adjustment
(10°F for each model) to assure efficiency in the
refrigerant system.
Note. A gas is superheated whenever its
temperature
is
higher
than
the
temperature
corresponding to its pressure at saturation. Example:
Refrigerant-22 at 69 pounds pressure has a temperature
of 40°F. If the suction pressure gage reads 69 pounds
and the temperature of the suction tube reads 50°F, the
gas is superheated 10OF.
b. Adjustment. Refer to figures 6-10 and 6-11
and check and adjust the superheat setting of the 4
1/2ton thermal expansion valve. The 2.1 ton thermal
expansion valve adjusts in the same manner.
c. Testing.
(1) Stop the air conditioner and allow the
suction line to warm up to ambient temperature. Remove
the sensing bulb from its location against the suction
line and place in an ice-water bath (820F).
(2) Start the air conditioner, remove the
sensing bulb from the ice-water bath and warm by hand
while feeling the suction line. If the suction line
temperature drops, the valve is operating correctly. Stop
air conditioner and reinstall the sensing bulb.
(3) If there is little or no change in suction line
temperature, the valve is defective and must be
replaced.
Caution: Do not warm sensing bulb in hand
longer than necessary to check operation of the
valve. The valve is wide open or nearly so during
this procedure and excessive flood-back of liquid
refrigerant into the suction line will damage the
compressor.
Figure 6-10. Thermal Expansion valve superheat
adjustment
6-12
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