Service Valves and Pumpdown
!WARNING
PERSONAL INJURY AND UNIT DAMAGE HAZARD
Failure to follow this warning could result in personal injury or equipment damage.
Never attempt to make repairs to existing service valves. Unit operates under high pressure. Damaged seats and o-rings should not be replaced. Replacement of entire service valve is required. 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 gauge ports for measuring system pressures and provide shutoff convenience for certain types of repairs. (See Fig. 15 and Fig. 16.)
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 (will no longer turn counter clockwise), the service port is not pressurized. To pressurize the service port, this valve must be moved off the back-seating position (turned clockwise slightly). The gage port in 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. All heat pumps are shipped with an adapter stub tube. This tube must be installed on the liquid service valve. After connecting the stub tube 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 industry accepted methods and materials. 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 evaporator coil have been evacuated, the valve stem can be turned counterclockwise until 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 counterclockwise until seated) before the service-port caps can be removed and hoses of gauge 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 to 9 ± 2 ft/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.
If the service valve is to be replaced, a metal barrier must be inserted between the valve and the unit to prevent damaging the unit exterior from the heat of the brazing operations.
!CAUTION
PERSONAL INJURY HAZARD
Failure to follow this caution may result in personal injury.
Wear safety glasses, protective clothing, and gloves when handling refrigerant.
Pumpdown Procedure
Service valves provide a convenient shutoff valve useful for certain refrigeration-system repairs. System may be pumped down to make repairs on low side without losing complete refrigerant charge.
1.Attach pressure gauge to suction service-valve gauge port.
2.Front seat liquid-line valve.
3.Start unit in cooling mode. Run until suction pressure reaches 5 psig (35kPa). Do not allow compressor to pump to a vacuum.
4.Shut unit off. Front seat suction valve.
STAINLESS
STEEL
STEM
SERVICE
PORT
ENTRANCE
BACK
SEAT
POSITION
FIELD SIDE
FRONT
SEAT
POSITION
FORGED BACK SEATING VALVE
A91435
Fig. 15 – Suction Service Valve (Back Seating) Used in Preferred and Evolution ACs and HPs.
FIELD
SIDE
STEM
SERVICE PORT
W/SCHRADER CORE
SEAT
BAR STOCK FRONT SEATING VALVE
A91447
Fig. 16 – Suction Service Valve (Front Seating) Used in Legacy RNC and Legacy Line ACs and HPs
NOTE: All outdoor unit coils will hold only factory-supplied amount of refrigerant. Excess refrigerant, such as in long-line applications, may cause unit to relieve pressure through internal pressure-relief valve (indicated by sudden rise of suction pressure) before suction pressure reaches 5 psig (35kPa). If this occurs, shut unit off immediately, front seat suction valve, and recover remaining pressure.
