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b. Remove all flux residue with brush and water while
material is still hot.
2. Use ″sil-fos″ or ″phos-copper″ for copper-to-copper only.
No flux is required.
3. Silver solder is used on copper-to-brass, copper-to-steel, or
copper-to-copper. Flux is required when using silver solder.
4. Fluxes should be used carefully. Avoid excessive applica-
tion and do not allow fluxes to enter into the system.
5. Proper brazing temperature of copper is when it is heated to
a dull red color.
This section on brazing is not intended to teach a technician how
to braze. There are books and classes that teach and refine brazing
techniques. The basic points above are listed only as a reminder.
IV. SERVICE VALVES
WARNING: Never attempt to make repairs to existing
service valves. Unit operates under high pressure. Dam-
aged seats and o-rings should not be replaced. Replace-
ment of entire service valve is required. Tampering with
damaged valves can cause personal injury or death.
Service valve must be replaced by properly trained
service technician.
Service valves provide a means for holding original factory charge
in outdoor unit prior to hookup to indoor coil. They also contain
gage ports for measuring system pressures and provide shutoff
convenience for certain types of repairs. (See Fig. 44.)
Two types of service valves are used in outdoor residential
equipment. The first type is a front-seating valve, which has a
service port that contains a Schrader fitting. The service port is
always pressurized after the valve is moved off the front-seat
position.
The second type is a combination front-seating/back-seating valve,
which has a metal-to-metal seat in both the open and closed
positions. When it is fully back-seated, the service port is not
pressurized. To pressurize the service port, this valve must be
moved off the back-seating position. This valve does not contain a
Schrader fitting. Both types of service valves are designed for
sweat connection to the field tubing.
The service valves in the outdoor unit come from the factory
front-seated. This means that the refrigerant charge is isolated from
the line-set connection ports. Some heat pumps are shipped with
sweat-adapter tube. This tube must be installed on the liquid-
service valve. After connecting the sweat adapter to the liquid-
service valve of a heat pump, the valves are ready for brazing. The
interconnecting tubing (line set) can be brazed to the service valves
using either silver-bearing or non-silver-bearing brazing material.
Consult local codes.
Before brazing the line set to the valves, the belled ends of the
sweat connections on the service valves must be cleaned so that no
brass plating remains on either the inside or outside of the bell
joint. To prevent damage to the valve and/or cap ″O″ ring, use a
wet cloth or other acceptable heat-sinking material on the valve
before brazing. To prevent damage to the unit, use a metal barrier
between brazing area and unit.
After the brazing operation and the refrigerant tubing and evapo-
rator coil have been evacuated, the valve stem can be turned
counterclockwise until it opens or back-seats, which releases
refrigerant into tubing and evaporator coil. The system can now be
operated.
Back-seating service valves must be back-seated (turned counter-
clockwise until seated) before the service-port caps can be re-
moved and hoses of gage manifold connected. In this position,
refrigerant has access from and through outdoor and indoor unit.
The service valve-stem cap is tightened to 20 ± 2 ft/lb torque and
the service-port caps to9±2ft/lb torque. The seating surface of
the valve stem has a knife-set edge against which the caps are
tightened to attain a metal-to-metal seal. If accessory pressure
switches are used, the service valve must be cracked. Then, the
knife-set stem cap becomes the primary seal.
The service valve cannot be field-repaired; therefore, only a
complete valve or valve stem and service-port caps are available
for replacement.
FIELD
SIDE
SERVICE PORT
W/SCHRADER
CORE
SEAT
STEM
FORGED FRONT SEATING VALVE
A91448
STEM
SERVICE PORT
W/SCHRADER CORE
SEAT
BAR STOCK FRONT SEATING VALVE
FIELD
SIDE
A91447
Fig. 44—Service Valves
—38—