Lennox Elite XC13 - Charging System

Page 22
506120−01 03/10
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
Drop
) = A minus C.
3. Determine if fan needs adjustmentIf the difference between the
measured T
Drop
and the desired DT (T
Drop
–DT) is within +3º, no
adjustment is needed. See examples: Assume DT = 15 and A temp. =
72º, these C temperatures would necessitate stated actions:
Cº T
Drop
– DT = ºF ACTION
53º 19 – 15 = 4 Increase the airflow
58º 14 – 15 = −1 (within +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 DT are within +3º.
DT
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 flowair flow
All temperatures are
expressed in ºF
INDOOR COIL AIRFLOW CHECK
Check indoor coil airflow using the Delta−T (DT) 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-INSUPERHEAT
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