Bryant 180B024 Application Manual And Service Manual Download Page 31

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Residential Air Conditioners and Heat Pumps Using R-22 and Puron® Refrigerant: Application Guideline and Service Manual

Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.

Thermostatic Expansion Valve (TXV)

All (post-2006) furnace coils, most fan coils and a few heat pumps have

a factory installed thermostatic expansion valve (TXV). The TXV will

be a bi-flow, hard-shutoff with an external equalizer and a balance port

pin. A hard shut-off TXV does not have a bleed port. Therefore,

minimal equalization takes place after shutdown. TXVs are specifically

designed to operate with Puron or R-22 refrigerant, use only factory

authorized TXV’s. 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 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

the following:

1. Superheat temperature is sensed by cap tube sensing bulb on

suction tube at outlet of evaporator coil. This temperature is

converted into pressure by refrigerant in the bulb pushing

downward on the diaphragm which opens the valve via the

pushrod(s).

2. The suction pressure at the outlet of the evaporator coil is

transferred via the external equalizer tube to the underside of the

diaphragm. This is needed to account for the indoor coil pressure

drop. Residential coils typically have a high pressure drop, which

requires this valve feature.

3. The pin is spring loaded, which exerts pressure on the underside of

the diaphragm. Therefore, the bulb pressure works against the

spring pressure and evaporator suction pressure to open the valve.

If the load increases, the temperature increases at the bulb, which

increases the pressure on the top side of the diaphragm. This opens

the valve and increases the flow of refrigerant. The increased

refrigerant 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.

Install TXV

The thermostatic expansion valve is specifically designed to operate

with a refrigerant type. Do not use an R-22 TXV on a Puron system, and

do not use a Puron valve on an R-22 system. Refer to Product Data Sheet

for the appropriate TXV kit number.

IMPORTANT:

The TXV should be mounted as close to the indoor coil

as possible and in a vertical, upright position. Avoid mounting the inlet

tube vertically down. The valve is more susceptible to malfunction due

to debris if inlet tube is facing down. A factory-approved filter drier

must be installed in the liquid line at the indoor unit.

Installing TXV in Place of Piston in a Rated Indoor Coil

(pre-2006)

1. Pump system down to 2 psig, if possible, and recover refrigerant.
2. Remove hex nut from piston body. Use backup wrench on fan coils.
3. Remove and discard factory-installed piston. Be sure Teflon seal is

in place.

4. Reinstall hex nut. Finger tighten nut plus 1/2 turn.

NOTE:

If the piston is not removed from the body, TXV will not

function properly.

5. Install TXV on indoor coil liquid line. Sweat swivel adapter to inlet

of indoor coil and attach to TXV outlet. Use backup wrench to

avoid damage to tubing or valve. Sweat inlet of TXV, marked “IN”

to liquid line. Avoid excessive heat which could damage valve.

6. Install vapor elbow with equalizer adapter to suction tube of line set

and suction connection to indoor coil. Adapter has a 1/4-in. male

connector for attaching equalizer tube.

7. Connect equalizer tube of TXV to 1/4-in. equalizer fitting on vapor

line adapter.

8. Attach TXV bulb to horizontal section of suction line using clamps

provided. Insulate bulb with field-supplied insulation tape. See

Fig. 27

for correct positioning of sensing bulb.

9. Proceed with remainder of unit installation.

A08083

Fig. 27 – Position of Sensing Bulb

Replacing TXV on an Indoor Coil (pre-2006)

1. Pump system down to 2 psig, if possible, and recover refrigerant.
2. Remove coil access panel and fitting panel from front of cabinet.
3. Remove TXV support clamp using a 5/16-in. nut driver. Save the

clamp.

4. Remove R-22 TXV using a backup wrench on flare connections to

prevent damage to tubing.

5. Using wire cutters, cut equalizer tube off flush with vapor tube

inside cabinet.

6. Remove bulb from vapor tube inside cabinet.
7. Braze equalizer stub-tube closed. Use protective barrier as

necessary to prevent damage to drain pan.

IMPORTANT:

Route the equalizer tube of TXV through suction line

connection opening in fitting panel prior to replacing fitting panel

around tubing.

8. Install TXV with 3/8-in. copper tubing through small hole in