9
Fixed Orifice
1. Temporarily install a thermometer 4-6" from the compres-
sor on the suction line. Ensure the thermometer makes ad-
equate contact and is insulated for best possible readings.
Use vapor temperature to determine superheat.
2. Refer to the superheat table provided for proper system su-
perheat. Add charge to lower superheat or recover charge to
raise superheat.
Expansion Valve System
NOTE: Units matched with indoor coils equipped with non-adjust-
able TXV should be charged by subcooling only.
1. Temporarily install a thermometer on the liquid line at the
liquid line service valve and 4-6" from the compressor on
the suction line. Ensure the thermometer makes adequate
contact and is insulated for best possible readings. Use liq-
uid line temperature to determine sub-cooling and vapor
temperature to determine superheat.
2. Check subcooling and superheat. Systems with TXV applica-
tion should have a subcooling of 7 to 9 ºF and superheat
of 7 to 9 ºF.
a.
If subcooling and superheat are low, adjust TXV to 7 to
9 ºF superheat, then check subcooling.
NOTE: To adjust superheat, turn the valve stem clock-
wise to increase and counter clockwise to decrease.
b.
If subcooling is low and superheat is high, add charge
to raise subcooling to 7 to 9 ºF then check superheat.
c.
If subcooling and superheat are high, adjust TXV valve
to 7 to 9 ºF superheat, then check subcooling.
d.
If subcooling is high and superheat is low, adjust TXV
valve to 7 to 9 ºF superheat and remove charge to
lower the subcooling to 7 to 9 ºF.
NOTE: Do NOT adjust the charge based on suction pressure un-
less there is a gross undercharge.
NOTE: Check the Schrader ports for leaks and tighten valve cores
if necessary. Install caps finger-tight.
Heat Pump - Heating Cycle
The proper method of charging a heat pump in the heat mode is by
weight with the additional charge adjustments for line size, line
length, and other system components. For best results, on out-
door units with TXVs, superheat should be 2-5° at 4-6" from the
compressor. Make final charge adjustments in the cooling cycle.
