12/03/2012
24
GI301
Superheat and Sub-Cooling
Comments
1.
This is a two TXV system – the heating TXV is internal to the main cabinet at the water coil refrigerant
entrance and the cooling TXV is located on the plenum air coil at the air coil liquid entrance.
2.
Begin in heating and check Superheat and Subcool associated with the TXV at the water coil
(evaporator) as follows.
3.
Depending upon findings and requirement for adjustment, next check Subcool and Superheat in cooling.
Determining Superheat
1.
Measure the temperature of the suction line at the point where the expansion valve bulb is clamped.
2.
Determine the suction pressure in the suction line by attaching refrigeration gauges to the Schrader
connection on the suction side of the compressor.
3.
Convert the pressure obtained in Step 2 to the saturation temperature by using the R-410A
Pressure/Temperature Conversion Chart on page 26.
4.
Subtract the temperature obtained in Step 3 from Step 1. The difference is the amount of superheat for
the unit. Refer to Unit Operating Conditions for superheat ranges at specific entering water conditions.
Superheat Adjustment
1.
Remove the seal cap from the bottom of the TXV valve.
2.
Turn the adjustment screw clockwise to increase superheat and counterclockwise to decrease superheat.
One complete 360° turn changes the superheat approximately 3-4° F. regardless of refrigerant type. You
may need to allow as much as 30 minutes after the adjustment is made for the system to stabilize.
3.
Once the proper superheat setting has been achieved, replace and tighten the seal cap.
Warning:
There
are 8 total (360°) turns on the superheat adjustment stem from wide open to fully closed. When
adjusting the superheat stem clockwise (superheat increase) and the stop is reached, any further
clockwise turning adjustment will damage the valve.
Determining Sub-Cooling
1.
Measure the temperature of the liquid line on the small refrigerant line (liquid line) feeding the air coil
cabinet.
2.
Measure the liquid line pressure by attaching refrigerant gauges to the Schrader connection on the liquid
line service valve.
3.
Convert the pressure obtained in Step 2 to the saturation temperature by using the R-410A
Pressure/Temperature Conversion Chart.
4.
Subtract the temperature in Step 1 from the temperature in Step 3. The difference will be the sub-
cooling value for that unit. Refer to Unit Operating Conditions chart for sub-cooling ranges at specific
enter water conditions.
Summary of Contents for TST-***
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