SERVICING
17
FINAL CHARGE ADJUSTMENT
The outdoor temperature must be 65°F to 105°F. If out-
door ambient temperature is out of range, charge defined
amount and don’t adjust subcooling. Set unit to CHARGE
mode.
After system has stabilized per startup instructions, check
subcooling as detailed in the following section.
In the event of system overcharge or undercharge, refriger-
ant in the system must be adjusted to the appropriate sub-
cooling and superheat as specified in the following sections.
Refrigerant amount should be adjusted /- 0.5 lb. if
the outdoor ambient temperature is greater than 65°F and
less than 105°F. Manufacturer recommends that the system
should be evacuated and should be charged the initial re-
frigerant for given line length when the ambient temperature
is less than 65°F and more than 105°F. Refer to the Installa-
tion Manual to calculate refrigerant amount.
5. With the system still running, remove hose and rein-
stall both valve caps.
6. Check system for leaks.
NOTE:
Subcooling information is valid only while the unit is
operating at 100% capacity or 100% of compressor speed
in CHARGE MODE. Compressor speed is displayed under
STATUS menu in the thermostat.
CHECKING COMPRESSOR EFFICIENCY
The reason for compressor inefficiency is that the com
-
pressor is broken or damaged, reducing the ability of the
compressor to pump refrigerant vapor. The condition of the
compressor is checked in the following manner.
1. Attach gauges to the high and low side of the system.
2. Start the system and run CHARGE MODE.
If the test shows:
a. Below normal high side pressure.
b. Above normal low side pressure.
c.
Low temperature difference across coil.
d. Low amp draw at compressor.
And the charge is correct. The compressor is faulty - re-
place the compressor.
CHECKING SUBCOOLING
Refrigerant liquid is considered subcooled when its tem-
perature is lower than the saturation temperature corre-
sponding to its pressure. The degree of subcooling equals
the degrees of temperature decrease below the saturation
temperature at the existing pressure.
1. Attach an accurate thermometer or preferably a ther-
mocouple type temperature tester to the liquid service
valve as it leaves the condensing unit.
2. Install a high side pressure gauge on the high side
(liquid) service valve at the front of the unit.
3. Record the gauge pressure and the temperature of
the line.
4.
Review the technical information manual or specifica
-
tion sheet for the model being serviced to obtain the
design subcooling.
5. Compare the hi-pressure reading to the “Required
Liquid Line Temperature” chart. Find the hi-pressure
value on the left column. Follow that line right to the
column under the design subcooling value. Where the
two intersect is the required liquid line temperature.
Alternately you can convert the liquid line pressure
gauge reading to temperature by finding the gauge
reading in the R-410A Pressure vs. Temperature
Chart, find the temperature in the °F. Column.
6.
The difference between the thermometer reading and
pressure to temperature conversion is the amount of
subcooling.
Add charge to raise subcooling. Recover charge to lower
subcooling.
Subcooling Formula = Sat. Liquid Temp. - Liquid Line
Temp.
EXAMPLE:
a. Liquid Line Pressure = 417 PSIG
b. Corresponding Temp. = 120°F.
c. Thermometer on Liquid line = 109°F.
To obtain the amount of subcooling subtract 109°F from
120°F.
The difference is 11° subcooling. See the specification
sheet or technical information manual for the design sub-
cooling range for your unit.
2 TON
10-12°F
3 TON
13-15°F
4 TON
8-10°F
5 TON
11-13°F
There are other causes for high head pressure which may
be found in the “Cooling / Heating Analysis Chart.”
If other causes check out normal, an overcharge or a sys-
tem containing non-condensables would be indicated.
If this system is observed:
1. Start the system.
2. Remove and capture small quantities of gas from
the suction line dill valve until the head pressure is
reduced to normal.
3. Observe the system while running a cooling perfor-
mance test. If a shortage of refrigerant is indicated,
then the system contains non-condensables.
