Vogt HEC-10, Service Manual

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HEC-Series Service Manual
SERVICE OPERATIONS
10/21/01
9-2
TXV Adjustment By Superheat. Superheat is the difference between the refrigerant vapor
temperature and its saturation temperature. (Translate the pressure reading to saturated temperature
and subtract it from the actual temperature reading.)
Follow this procedure:
1. Attach an accurate pressure gage to the low pressure test connection.
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. Set the selector switch to make crushed ice.
5. 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. Refer to the chart below for recommended
superheat ranges.
6. 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.
Model Minimum Target Maximum
HEC-10 7 8 10
HEC-20 5 6 8
HEC-30 7 8 10
HEC-40 8 10 11
TABLE 9-1
Recommended Superheat Range
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, the valve must be
replaced.