Bryant R-22 service manual TXV Superheat Setting AT Outlet of Evaporator Coil, IX. Coil Removal

TABLE 20—TXV SUPERHEAT SETTING AT OUTLET OF EVAPORATOR COIL

INSTALLATION	TXV TYPE	PRODUCT USAGE	SUPERHEAT SETTING
Field Accessory	RPB/HSO	Air Conditioner Indoor Unit	10°
Field Accessory	RPB/HSO	Heat Pump Indoor Unit	6°
Field Accessory/Factory-Installed	HSO	Indoor Fan Coil Unit	6°
Factory-Installed	HSO	2-Speed Heat Pump Outdoor Unit	4°
Factory-Shipped/Field-Installed	HSO	2-Speed Indoor Unit	4°

FROM		TO		TO INDOOR COIL
	ACCUMULATOR
OUTDOOR			VIA SERVICE VALVE
COIL			ON OUTDOOR COIL
		INSULATE
			FOR	TP-2
TP-4	TP-3	ACCURATE

READING

INSULATE FOR

ACCURATE TP-1

READING

FROM COMPRESSOR

DISCHARGE LINE

ELECTRONIC

THERMOMETER

A88341

Fig. 48—Reversing Valve (Heating Mode, Solenoid De-

Energized)

Hard Shutoff (HSO)—Has no bleed port and allows no bleed- through after system shutdown. No pressure equalization occurs. Because of unequalized system pressures, a start capacitor and relay must be installed on single-phase reciprocating compressors to start the compressor.

See Table 20 for TXV superheat settings. These settings are factory set and are not field adjustable. Table 17 settings are for Bryant-approved accessories and factory-installed TXVs only.

VIII. THERMOSTATIC-EXPANSION VALVE (BI-FLOW TXV)

The standard TXV is a metering device that is used in condensing and heat pump systems to adjust to changing load conditions by maintaining a preset superheat temperature at the outlet of the evaporator coil. The volume of refrigerant metered through the valve seat is dependent upon:

1.Superheat temperature sensed by cap-tube sensing bulb on suction tube at outlet of evaporator coil. As long as this bulb and cap tube contains some liquid refrigerant, this tempera- ture is converted into suction pressure pushing downward on the diaphragm, which tends to open the valve via the pushrods.

2.The suction pressure at the outlet of the evaporator coil is transferred via the external equalizer tube to the underside of the diaphragm.

3.The needle valve on the pin Bryant is spring-loaded, which also exerts pressure on the underside of the diaphragm via the pushrods, which 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 Bryant away from the seat, opening the valve and increasing the flow of refrigerant. The increased refrigerant flow causes

—41—

increased leaving evaporator pressure, which is transferred via the equalizer tube to the underside of the diaphragm. This tends to cause the pin-Bryant spring pressure to close the valve. The refrigerant flow is effectively stabilized to the load demand with negligible change in superheat. The bi-flow TXV is used on split-system heat pumps. In the cooling mode, the TXV operates the same as the standard TXV previously explained. (See Fig. 49.)

However, when the system is switched to the heating mode of operation, the refrigerant flow is reversed. The bi-flow TXV has an additional internal-check valve and external tubing. (See Fig. 50.) These additions allow the refrigerant to bypass the TXV when refrigerant flow is reversed with only a 1- to 2-psig pressure drop through the device. When the heat pump switches to the defrost mode, the refrigerant flows through a completely open (unthrottled) TXV, and the bulb senses the residual heat of the outlet tube of the coil that had been operating in the heating mode (about 85°F and 155 psig). This temporary, unthrottled valve decreases the indoor-pressure drop, which in turn increases the refrigerant-flow rate, decreases overall defrost time, and enhances defrost efficiency.

IX. COIL REMOVAL

Coils on this family of units are easy to remove, if required for compressor removal or replacement coil.

CAUTION: Wear safety glasses and gloves when han- dling refrigerants.

To remove or replace coil:

1.Shut off all power to unit.

2.Remove and recover refrigerant from system through ser- vice valves.

3.Remove top cover. (See Remove Top Cover section.)

4.Remove screws in base pan to coil grille.

5.Remove coil grille from unit.

6.Remove screws on corner-post (Reliant) service-valve panel (Cube unit) holding coil-tube sheet.

CAUTION: Cut tubes to reduce the possibility of fire and personal injury.

7.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.

8.Lift coil vertically from basepan. Place aside carefully.

9.Reverse procedure to reinstall coil.

X. LIQUID-LINE STRAINER (HEAT PUMPS ONLY)

The liquid-line strainer is upstream of the heating piston. The strainer catches debris in the liquid line during heating mode. If it becomes plugged, system operation and pressure become abnor- mal, and the compressor may become hot and cycle off on the overloads or pressure relief.