Lennox AC13 -018 Installation Instructions Manual page 17

SETTING UP TO CHECK CHARGE
1. Close manifold gauge set valves. Connect the center
manifold hose to an upright cylinder of HCFC−22.
2. Connect the manifold gauge set to the unit's service
ports as illustrated in figure 3.
S low pressure gauge to suction service port
S high pressure gauge to liquid service port
Temp.
80 24 24 24 23 23 22 22 22 20 19 18 17 16 15
of air
entering
78 23 23 23 22 22 21 21 20 19 18 17 16 15 14
indoor
76 22 22 22 21 21 20 19 19 18 17 16 15 14 13
coil ºF
74 21 21 21 20 19 19 18 17 16 16 15 14 13 12
A 72 20 20 19 18 17 17 16 15 15 14 13 12 11 10
70 19 19 18 18 17 17 16 15 15 14 13 12 11 10
Wet−bulb ºF
57 58 59 60 61 62 63 64 65 66 67 68 69 70
T
Drop
C
19º
53º
air flow
DRY
BULB
All temperatures are
expressed in ºF
Figure 32. Checking Indoor Airflow over Evaporator Coil using Delta−T Chart
START: Determine how refrigerant is metered
WHEN TO CHARGE?
S
Warm weather best
S
Can charge in colder weather
CHARGE METHOD? Determine by:
S
Metering device type
S
Outdoor ambient temperature
REQUIREMENTS:
S
Sufficient heat load in structure
S
Indoor temperature between 70-80ºF
(21−26ºC)
S
Manifold gauge set connected to unit
S
Thermometers:
− to measure outdoor ambient
temperature
− to measure liquid line temperature
− to measure suction line
temperature
DT
B
A
72º
air flow B
64º
DRY
BULB
INDOOR WET
BULB
COIL
TXV
65ºF
(18.3ºC) and
Above
APPROACH OR
SUBCOOLING
Figure 33. Determining Charge Method
INDOOR AIRFLOW CHECK
Check indoor airflow using the Delta−T (
the illustration in figure 32.
DETERMINING CHARGE METHOD
Use the illustration in figure 33 to determine the correct
charging method.
1. Determine the desired DT Measure entering air temperature
using dry bulb (A) and wet bulb (B). DT is the intersecting value of A
and B in the table (see triangle).
2. Find temperature drop across coil Measure the coil's dry bulb
entering and leaving air temperatures (A and C). Temperature Drop
Formula: (T ) = A minus C.
Drop
3. Determine if fan needs adjustment If the difference between the
and the desired DT (T
measured T
Drop
justment is needed. See examples: Assume DT = 15 and A temp. =
72º, these C temperatures would necessitate stated actions:
DT
Cº T –
Drop
53º 19 – 15
58º 14 – 15
62º 10 – 15
4. Adjust the fan speed See indoor unit instructions to in-
crease/decrease fan speed.
Changing air flow affects all temperatures; recheck temperatures to
confirm that the temperature drop and DT are within +3º.
Which
metering
device?
64ºF
(17.7ºC) and
Below
WEIGH-IN
Page 17
DT)
–DT) is within +3º, no ad-
Drop
=
ºF ACTION
=
4 Increase the airflow
=
−1 (within +3º range) no change
=
−5 Decrease the airflow
RFC
40ºF
(4.4ºC) and (3.8ºC) and
Above
Below
SUPERHEAT WEIGH-IN
process using
39ºF
AC13 SERIES