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9-2
SERVICE OPERATIONS
Expansion Valve. The expansion valve was adjusted before shipment and it is rarely necessary to
change this setting.
If considerably less ice than shown in TABLE 11-5 is being produced per discharge, check the water
supply, circulating water pump, water distributors, liquid line valve, refrigerant level, freezer
pressure switch and all other avenues BEFORE changing the factory setting of the expansion valve.
Vogt Part #: 12A4200C0503
Superheat. Superheat is the difference between the refrigerant vapor temperature and its saturation
temperature. (Translate the pressure to saturated temperature and subtract from the actual temperature.)
Checking Superheat. Follow this procedure:
1. Attach an accurate pressure gage to the freezer-charging valve (#28).
2. Using a digital thermometer, attach the thermocouple to the suction line directly below and in-
line with the existing TXV sensing bulb.
3. Hold the thermocouple in place with tape and insulation to assure good contact and a true reading.
4. Operate the machine and monitor the superheat during the freeze cycle after the first four
minutes and at two minute intervals for at least two cycles.
5. Adjust the valve only 1/4 turn at a time. Close (turn stem in) to raise superheat. Open (turn stem
out) to lower superheat. Monitor at least two cycles after each adjustment before adjust further.
If the valve cannot be adjusted satisfactorily, check the bulb insulation as follows:
1. Remove the insulation from the sensing bulb.
2. Loosen the bulb clamps and remove the bulb.
3. Clean and polish the sensing bulb and suction line to assure maximum contact between them.
4. Install the bulb in the same place tightening the clamps securely.
5. Replace the insulation around the bulb making sure it is well sealed. Repeat the adjustment
procedure and if you are still unable to accomplish the proper superheat setting, replace valve.
When installing a new valve, be sure to use the proper soldering techniques to prevent overheating
the valve body, which could damage the superheat spring and result in flood back problems.
When soldering:
1. Wrap a wet cloth around the valve body and element.
2. Direct the flame away from the valve body.
3. Apply only enough heat to flow the alloy material into all the joint areas. Do not overheat.
4. After the brazing alloy has set, quench or apply a wet brush or swab to remove the flux residue.
Use Emery cloth or a wire brush if necessary.
4/2/14
FIGURE 9-2
Thermal Expansion Valve
03TA Service Manual
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