Lennox Merit Series13ACD Installation Instructions Manual page 15

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 27. Checking Indoor Airflow over Evaporator Coil using Delta−T Chart
START: Determine how refrigerant is metered
WHEN TO CHARGE?
S
Warm weather best
S
Can charge in colder weather
CHARGE METHOD? Determine by:
S
Metering device type
S
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
START: Measure outdoor ambient temperature
USE EITHER APPROACH
OR SUBCOOLING
METHOD
WEIGH IN TXV/RFC
Refrigerant Charge per Line Set Length
Ounces per 5 feet (g per 1.5 m)
Liquid Line
adjust from 15 feet (4.6 m) line set*
Set Diameter
3/8" (9.5 mm)
3 ounce per 5' (85 g per 1.5 m)
NOTE − *If line length is greater than 15 ft. (4.6 m), add this
amount. If line length is less than 15 ft. (4.6 m), subtract this
amount.
Delta−T
B
A
72º
B
air flow
64º
DRY
BULB
INDOOR
WET
BULB
COIL
APPROACH OR
Figure 28. Determining Charge Method
Above or
below 65ºF
(18ºC)?
ABOVE
Figure 29. HCFC−22 Weigh In TXV Method
1. Determine the desired DT Measure entering air temperature
using dry bulb (A) and wet bulb (B). DT 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 ) = A minus C.
Drop
3. Determine if fan needs adjustment If the difference between the
measured T and the desired DT (T
Drop
justment is needed. See examples: Assume DT = 15 and A temp. =
72º, these C temperatures would necessitate stated actions:
Cº T – DT
Drop
53º 19 – 15
58º 14 – 15
62º 10 – 15
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 DT are within +3º.
TXV
Above 65ºF
(18ºC)?
SUBCOOLING
BELOW
Page 15
–DT) is within +3º, no ad-
Drop
= ºF ACTION
= 4 Increase the airflow
= −1 (within +3º range) no change
−5 Decrease the airflow
=
RFC
Which
metering
device?
Below 65ºF Above 40ºF
(18ºC)?
WEIGH-IN SUPERHEAT
1. Check Liquid and suction line pressures
2. Compare unit pressures with Table 6,
Normal Operating Pressures.
3. Conduct leak check;
previously outlined.
4. Weigh in the unit nameplate charge plus
any charge required for line set differences
over feet.
This nameplate is for illustration purposes
only. Go to actual nameplate on outdoor
unit for charge information.
(4ºC)?
evacuate as
13ACD SERIES