Lennox Merit 14ACX−018−230 Installation Instructions Manual page 23

CHECKING AIR FLOW AT INDOOR COIL
Check airflow using the Delta−T (
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 19. Checking Indoor Airflow over Evaporator Coil using Delta−T Chart
START: Determine how refrigerant is metered
WHEN TO CHARGE?
S
Best during warm weather
S
Can charge in colder weather by determining
best charge method? Determine by:
A Metering device type
B 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)
process using the illustration in figure 19.
DT
B
A
72º
air flow B
64º
DRY
BULB
INDOOR WET
BULB
COIL
65ºF
(18.3ºC) and
Above
APPROACH OR
SUBCOOLING
Figure 20. Determining Charge Method
1. Determine the desired DT Measure entering air temper-
ature using dry bulb (A) and wet bulb (B). DT is the intersect-
ing value of A and B in the table (see triangle).
2. Find temperature drop across coil
bulb entering and leaving air temperatures (A and C). Tem-
perature Drop Formula: (T
3. Determine if fan needs adjustment
the measured T
Drop
+3º, no adjustment is needed. See examples: Assume DT =
15 and A temp. = 72º, these C temperatures would necessi-
tate stated actions:
DT
T –
Cº
Drop
19 – 15
53º
14 – 15
58º
10 – 15
62º
4. Adjust the fan speed
crease/decrease fan speed.
Changing air flow affects all temperatures; recheck tempera-
tures to confirm that the temperature drop and DT are within
+3º.
Which
metering
device?
TXV
64ºF
(17.7ºC) and
Below
WEIGH-IN
Page 23
Measure the coil's dry
) = A minus C.
Drop
If the difference between
and the desired DT (T
–DT) is within
Drop
=
ºF ACTION
=
4 Increase the airflow
=
−1 (within +3º range) no change
=
−5 Decrease the airflow
See indoor unit instructions to in-
RFC
40ºF
(4.4ºC) and (3.8ºC) and
Above
SUPERHEAT WEIGH-IN
39ºF
Below
14ACX SERIES