Page 22
506120−01 03/10
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
adjustment 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/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
INDOOR COIL AIRFLOW CHECK
Check indoor coil airflow using the Delta−T (
D
T)
process as illustrated.
Figure 33. Indoor Coil Airflow Check
Charging System
WHEN TO CHARGE?
Warm weather best
Can charge in colder weather
CHARGE METHOD?
Determine by:
Metering device type
Outdoor ambient temperature
REQUIREMENTS:
Sufficient heat load in structure
Indoor temperature between 70-80ºF
(21−26ºC)
Manifold gauge set connected to unit
Thermometers:
−
to measure outdoor ambient temperature
−
to measure liquid line temperature
−
to measure suction line temperature
TXV
FIXED
ORIFICE
APPROACH OR
SUBCOOLING
WEIGH-IN
SUPERHEAT
65ºF
(18.3ºC) and
Above
START: Determine how refrigerant is metered
39ºF
(3.8ºC) and
Below
Which indoor
metering
device?
WEIGH-IN
64ºF
(17.7ºC) and
Below
40ºF
(4.4ºC) and
Above
DETERMINING CHARGE METHOD
A
B
C
D
E
Figure 34. Determining Charge Method
