SERVICING
S-106 OVERFEEDING
Overfeeding by the expansion valve results in high suction pres- sure, cold suction line, and possible liquid slugging of the com- pressor.
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 15 to 18 degrees superheat of the suction gas. Before checking the superheat or replacing the valve, perform all the procedures outlined under Air Flow, Refrigerant Charge, Expansion Valve - Overfeeding, Underfeeding. These are the most common causes for evaporator malfunction.
CHECKING SUPERHEAT
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 ex- isting pressure. See Temperature - Pressure Chart on follow- ing pages.
1.Run system at least 10 minutes to allow pressure to sta- bilize.
2.Temporarily install thermometer on suction (large) line near suction line service valve with adequate contact and insulate for best possible reading.
3.Refer to the superheat table provided for proper system superheat. Add charge to lower superheat or recover charge to raise superheat.
Superheat Formula = Suct. Line Temp. - Sat. Suct. Temp.
EXAMPLE:
a.Suction Pressure = 143
b.Corresponding Temp. °F. = 50
c.Thermometer on Suction Line = 66°F.
To obtain the degrees temperature of superheat, subtract 50.0 from 66.0°F.
The difference is 16° Superheat. The 16° Superheat would fall in the ± range of allowable superheat.
See R410A Pressure vs. Temperature chart on page 40.
SUPERHEAT AND SUBCOOLING ADJUSTMENT ON TXV APPLICATIONS
Single Speed Application (*PH1524**-*PH1536**)
1.Purge gauge lines. Connect service gauge manifold to access fittings. Run system at least 10 minutes to allow pressure to stabilize.
2.Temporarily install thermometer on liquid (small) line near liquid line access fitting with adequate contact and insu- late for best possible reading.
3.Check subcooling and superheat. Systems with TXV ap- plication should have a subcooling of 10 + 2°F and super- heat of 15 to 18ºF.
a.If subcooling and superheat are low, adjust TXV to 15 - 18ºF then check subcooling.
b.If subcooling is low and superheat is high, add charge to raise subcooling to10 ± 2ºF then check super- heat.
c.If subcooling and superheat are high, adjust TXV valve to 15 - 18ºF then check subcooling.
d.If subcooling is high and superheat is low, adjust TXV valve to 15 to 18ºF superheat and remove charge to lower the subcooling to 10 ± 2ºF.
The TXV should NOT be adjusted at light load conditions 55º to 60ºF, under such conditions only the subcooling can be evaluated. This is because suction pressure is dependent on indoor airflow, and wet bulb temperature. NOTE: Do NOT adjust charge based on suction pressure unless there is a gross undercharge.
4. Disconnect manifold set. Installation is complete.
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