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506663−01 11/10
CHECKING AIR FLOW AT INDOOR COIL
Check airflow using the Delta−T (
D
T)
process using the illustration in figure 19.
1. Determine the desired
D
T
Measure entering air temper-
ature using dry bulb (
A
) and wet bulb (
B
).
D
T
is the intersect-
ing 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
). Tem-
perature Drop Formula: (
T
Drop
) =
A
minus
C
.
3. Determine if fan needs adjustment
If the difference between
the measured
T
Drop
and the desired
D
T
(T
Drop
–
D
T)
is within
+3º, no adjustment is needed. See examples: Assume
D
T
=
15 and
A
temp. = 72º, these
C
temperatures would necessi-
tate stated actions:
Cº
T
Drop
–
D
T
=
ºF
ACTION
53º
19
–
15
=
4
Increase the airflow
58º
14
–
15
=
−1
(3º range) no change
62º
10
–
15
=
−5
Decrease the airflow
4. Adjust the fan speed
See indoor unit instructions to in-
crease/decrease fan speed.
Changing air flow affects all temperatures; recheck tempera-
tures to confirm that the temperature drop and
D
T are within
+3º.
D
T
80
24 24 24 23 23 22 22 22 20 19 18 17 16 15
78
23 23 23 22 22 21 21 20 19 18 17 16 15 14
76
22 22 22 21 21 20 19 19 18 17 16 15 14 13
74
21 21 21 20 19 19 18 17 16 16 15 14 13 12
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
57 58 59 60 61 62 63 64 65 66 67 68 69 70
Temp.
of air
entering
indoor
coil ºF
INDOOR
COIL
DRY
BULB
DRY
BULB
WET
BULB
B
T
Drop
19º
A
Dry−bulb
Wet−bulb ºF
A
72º
B
64º
C
53º
air flow
air flow
All temperatures are
expressed in ºF
Figure 19. Checking Indoor Airflow over Evaporator Coil using Delta−T Chart
START: Measure outdoor ambient temperature
64ºF
(17.7ºC) and
BELOW
1. Check Liquid and suction line pressures
2. Compare unit pressures with table 5 or 6.
3. Conduct leak check; evacuate as
previously outlined.
4. Weigh in the unit nameplate charge plus
any charge required for line set differences
over feet.
Liquid Line
Set Diameter
g per 1.5 m) adjust from 4.6 m line
set*
9.5 mm
85 g per 1.5 m)
NOTE − *If line length is greater than 4.6 m, add this amount. If
line length is less than 4.6 m, subtract this amount.
Refrigerant Charge per Line Set Length
USE SUBCOOLING
METHOD
This nameplate is for illustration purposes
only. Go to actual nameplate on outdoor
unit for charge information.
ABOVE or
BELOW
Figure 20. HFC−410A Weigh In
65ºF
(18.3ºC)
and
ABOVE
