Page 20
507994-01 11/19
CHECKING AIR FLOW AT INDOOR COIL
Check airflow using the Delta-T (
D
T)
process using the illustration in figure 18.
1. Determine the desired
D
T
—Measure entering air temperature
using dry bulb (
A
) and wet bulb (
B
).
D
T
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
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 3º, no ad
justment is needed. See examples: Assume
D
T
= 15 and
A
temp. =
72º, these
C
temperatures would necessitate 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 increase/de
crease fan speed.
Changing air flow affects all temperatures; recheck temperatures to
confirm that the temperature drop and
D
T are 3º.
Delta
−
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 18. 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 3 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
65ºF
(18.3ºC) and
ABOVE
Figure 19. HFC-410A Weigh In
START: Measure outdoor ambient temperature
USE WEIGH‐IN METHOD
Weigh‐in or remove refriger
ant based upon line length
APPº (Approach) Values(F:+/-1.0° [C: +/-0.6°])
1. Confirm proper airflow across coil using figure 18.
2. Compare unit pressures with Table 3,
Normal Operating Pressures
.
3. Set thermostat to call for heat (must have a cooling load between
70‐80ºF (21-26ºC).
4. Connect gauge set.
5. When heat demand is satisfied, set thermostat to call for cooling.
6. Allow temperatures and pressures to stabilize.
7. Record outdoor ambient temperature:
AMBº =_________
8. Record liquid line temperature:
LIQº = __________
9. Subtract to determine approach (APPº):
LIQº_____ - AMBº _____ = APPº_____
10. Compare results with table below.
64ºF and
BELOW
65ºF and
ABOVE
ABOVE or
BELOW
If value is
MORE
than shown, remove
refrigerant.
If value is
LESS
than shown, add
refrigerant.
If refrigerant is added
or removed, verify
charge using the
Subcooling Method
.
MORE
or
LESS
ºF (ºC)*
-036
-042
-048
-060
Any
11 (6.1)
9 (5.0)
8 (4.4)
9 (5.0)
*Temperature of air entering outdoor coil
Figure 20. HFC-410A Approach TXV Charge
