SERVICING
COOLINGHEATING
THERMOSTATIC EXPANSION VALVES
Some TXV valves contain an internal check valve thus eliminating the need for an external check valve and bypass loop. The three forces which govern the operation of the valve are: (1) the pressure created in the power assembly by the feeler bulb, (2) evaporator pressure, and (3) the equivalent pressure of the superheat spring in the valve.
0% bleed type expansion valves are used on indoor and outdoor coils. The 0% bleed valve will not allow the system pressures (High and Low side) to equalize during the shut down period. The valve will shut off completely at approxi- mately 100 PSIG.
30% bleed valves used on some other models will continue to allow some equalization even though the valve has
The bulb must be securely fastened with two straps to a clean straight section of the suction line. Application of the bulb to a horizontal run of line is preferred. If a vertical installation cannot be avoided, the bulb must be mounted so that the capillary tubing comes out at the top.
THE VALVES PROVIDED BY GOODMAN ARE DESIGNED TO MEET THE SPECIFICATION REQUIREMENTS FOR OPTIMUM PRODUCT OPERATION. DO NOT USE SUB- STITUTES.
S-106 OVERFEEDING
Overfeeding by the expansion valve results in high suction pressure, cold suction line, and possible liquid slugging of the compressor.
If these symptoms are observed:
1.Check for an overcharged unit by referring to the cooling performance charts in the servicing section.
2.Check the operation of the power element in the valve as explained in
3.Check for restricted or plugged equalizer tube.
S-107 UNDERFEEDING
Underfeeding by the expansion valve results in low system capacity and low suction pressures.
If these symptoms are observed:
1.Check for a restricted liquid line or drier. A restriction will be indicated by a temperature drop across the drier.
2.Check the operation of the power element of the valve as described in
S-108 SUPERHEAT
The expansion valves are factory adjusted to maintain 12 to 18 degrees superheat of the suction gas. Before checking the superheat or replacing the valve, perform all the proce- dures outlined under Air Flow, Refrigerant Charge, Expan- sion Valve - Overfeeding, Underfeeding. These are the most common causes for evaporator malfunction.
CHECKINGSUPERHEAT
Refrigerant gas is considered superheated when its tempera- ture is higher than the saturation temperature corresponding to its pressure. The degree of superheat equals the degrees of temperature increase above the saturation temperature at existing pressure. See Temperature - Pressure Chart Table 7.
1.Attach an accurate thermometer or preferably a thermo- couple type temperature tester to the suction line at a point at least 6" from the compressor.
2.Install a low side pressure gauge on the suction line ser- vice valve at the outdoor unit.
3.Record the gauge pressure and the temperature of the line.
4.Convert the suction pressure gauge reading to tempera- ture by finding the gauge reading in Temperature - Pres- sure Chart and reading to the left, find the temperature in the °F. Column.
5.The difference between the thermometer reading and pres- sure to temperature conversion is the amount of super- heat.
EXAMPLE:
a.Suction Pressure = 84
b.Corresponding Temp. °F. = 50
c.Thermometer on Suction Line = 63°F.
To obtain the degrees temperature of superheat subtract 50.0 from 63.0°F.
The difference is 13° Superheat. The 13° Superheat would fall in the ± range of allowable superheat.
SUPERHEAT ADJUSTMENT
The expansion valves used on Amana® brand coils are factory set and are not field adjustable. If the superheat setting becomes disturbed, replace the valve.
On systems using capillary tubes or flow control restrictors, superheat is adjusted in accordance with the "DESIRED SUPERHEAT vs. OUTDOOR TEMP" chart as explained in section
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