Page 17
Step 1. Determine the desired
D
T
Measure entering air tempera-
ture using dry bulb (
A
) and wet bulb (
B
).
D
T
is the intersecting value
of
A
and
B
in the table (see triangle).
Step 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
.
Step 3. Determine if fan needs adjustment
If the difference be-
tween 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 necessitate stated ac-
tions:
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
Step 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
D
T are 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 20
Setup for Checking and Adding Charge
SETUP FOR CHARGING
low pressure gauge to
vapor service port
high pressure gauge to
liquid service port
Close manifold gauge set valves. Connect the center man-
ifold hose to an upright cylinder of HFC−410A.
CALCULATING CHARGE
If the system is void of refrigerant, first, locate and repair
any leaks and then weigh in the refrigerant charge into the
unit. To calculate the total refrigerant charge:
Amount
specified
on
nameplat
e
Adjust amt. for
variation in
line set length
(table 6)
Additional charge
specified per
indoor unit match−up
(table 7)
Total
charge
+
+
=
