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Determining Superheat

Table 14-1(A). - Determining Superheat

STEP	ACTION
1.	Obtain the temperature of the suction line at the point where the TEV sensing bulb is attached. a. Take the temperature reading with a dial thermometer similar to the one shown in figure 14-20(E), or use some other temperature measuring device that senses surface temperatures accurately.
2.	Obtain the suction pressure inside the piping at the location of the remote sensing bulb. a. If the valve is externally equalized, you can place a gauge in the external equalizer line. This is the most accurate method. b. The alternate method is to read the manifold pressure gauges at the compressor and add the estimated pressure drop through the suction line between the bulb and compressor. The sum of the two pressures provides approximate pressure at the location of the remote bulb.
3.	Convert the pressure you received in step 2 into saturated evaporator pressure. a. Use a pressure temperature chart. When using the chart, ensure that you are looking at the proper refrigerant.
4.	Simply subtract the temperature in step 3 from the temperature in step 1. This is superheat.

Note: When adjusting the expansion valve, turn the adjusting stem no more than one full turn and wait approximately 15-30 minutes for the system to balance out. Once the system is balanced, recheck the superheat setting by following the steps in table 14-1(A).

RECEIVERS AND ACCUMULATORS

The receiver is a storage tank for liquid refrigerant. When a refrigeration system is equipped with a receiver, you can close the outlet valve (king valve) and pump refrigerant into the receiver. This enables you to store the refrigerant while you work on the unit. Additionally, when a unit is equipped with a receiver, the quantity of refrigerant in the system is less critical than a unit not so equipped. Figure 14-23 shows the location of a receiver installed in a system. This is a commercial system with an air-cooled condenser, a thermostatic expansion valve, and a V type of reciprocating compressor.