FIGURE 27
MANOMETER
UNIT
Page 28
WARNING
Do not exceed nameplate charge under any con
ditions. Compressor damage will result.
1- This method uses a thermometer inserted in the
thermometer wells to check liquid line temperature.
Make sure thermometer wells are filled with oil be
fore checking.
2- IMPORTANT - Block compressor compartment with
access panel so air will not by-pass the coils.
3- Operate unit (all compressors) for at least five minutes
until pressures stabilize.
TABLE 3
APPROACH TEMPERATURE
UNIT
Degrees F Liquid Line Warmer Than Outdoor Air
CHA16-1853
7°F + 1 (3.9°C + 0.5)
CHA16823 7°F + 1 (3.9°C + 0.5)
CHA16953
8°F +
1 (4.5°C + 0.5)
6°F +
1 (3.3°C + 0.5)
6°F +
1 (3.3°C + 0.5)
CHA161353
CHA161603
7°F +
1 (3.9°C + 0.5)
CHA162553*
7°F +
1 (3.9°C + 0.5)
CHA162753*
7°F +
1 (3.9°C + 0.5)
CHA163003*
7°F +
1 (3.9°C + 0.5)CHA162553
1st Stage 2nd Stage
8°F + 1 (4.5°C + 0.5)
8°F +
1 (4.5°C + 0.5)CHA162753
10°F +
1 (5.6°C + 0.5)
CHA163003
*Round cornered condenser coils.
Slab type condenser coils.
10°F + 1 (5.6°C + 0.5)
8°F +
1 (4.5°C + 0.5)
9°F +
1 (5.1°C + 0.5)
4- Check each stage separately with all stages operat
ing. Compare liquid temperatures to outdoor ambient
temperature. Liquid line temperature should be a few
degrees warmer than the outdoor air temperature.
Table 3 shows how much warmer the liquid line should
be. For best results use same thermometer for both
readings.
Add refrigerant to make the liquid line cooler.
Recover refrigerant to make the liquid line warmer.
VII-INDOOR BLOWER
OPERATION / ADJUSTMENT
A-Blower Operation
NOTE-The following is a generalized procedure and
does not apply to all thermostat control systems.
1- Blower operation is dependent on the thermostat con
trol system option that has been installed in the
CHA16. Refer to the operation sequence for the con
trol system installed for detailed descriptions of blower
operation.
2- Generally, blower operation is set at the thermostat fan
switch. With the fan switch in ON" position, the blower
operates continuously. With the fan switch in AUTO"
position, the blower cycles with demand (or, with some
control systems, runs continuously while the heating or
cooling circuits cycle).
3- In most cases, the blower and entire unit will be off
when the system switch is in the OFF" position. The
only exception is immediately after a heating demand
until blower control switches off.
B-Determining Unit CFM
1- The following measurements must be made with a dry
indoor coil. Run the blower without the cooling de
mand. Air filters must be in place when measurements
are taken.
2- Measure static pressure external to the unit (from sup
ply to return).
To Measure Discharge Static Pressure:
a- Locate taps as shown in figure 27.
b- Punch a 1/4" diameter hole. Insert manometer hose
flush with the inside edge of hole or insulation. Seal
around the hole with perma
gum. Connect the zero end
of the manometer to the dis
charge (supply) side of the
system. Connect the other
end of the manometer to the
return duct as above.
c- With only the blower motor
running, observe manometer reading.
d- Seal around the hole when the check is com
plete.
3- Measure indoor blower wheel RPM (figure 28).
4- Refer to unit nameplate to determine the blower motor
horsepower.
5- Use the static pressure and RPM readings to deter
mine unit CFM.
6- The CFM can be adjusted at the motor pulley (see
section C-Blower Belt Adjustment).
Determining Unit CFM (Alternative Method):
Air volume may also be determined by measuring pres
sure drop across the indoor coil.
1- Remove lifting lug bolt located on the blower side of
unit above condensate drain. Use an awl or screw
driver to open a hole in the insulation.
2- Insert the positive or high pressure hose of draft
gauge 1 inch past the insulation.
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