Lennox XP21 Series Installation Instructions Manual page 28

ADDING OR REMOVING REFRIGERANT
This system uses HFC−410A refrigerant which operates at
much higher pressures than HCFC−22. The pre−installed
liquid line filter drier is approved for use with HFC−410A
only. Do not replace it with components designed for use
with HCFC−22.
COOLING MODE INDOOR AIRFLOW CHECK
Check airflow using the Delta−T (
illustration in figure 20.
HEATING MODE INDOOR AIRFLOW CHECK
Blower airflow cubic feet per minute (CFM) may be
calculated by energizing electric heat and measuring:
AIRFLOW
DRY
BULB
C
53º
All temperatures are expressed in ºF
Use the following procedure to adjust for optimal air flow across the indoor coil:
1. Determine the desired DT
table (see triangle).
2. Find temperature drop across coil
(T ) = A minus C.
Drop
3. Determine if fan needs adjustment
is needed. See example below:
ASSUME DT = 15 AND A TEMP. = 72º, THESE C TEMPERATURES WOULD NECESSITATE STATED ACTIONS:
DT =
Cº
T –
DROP
=
53º
19 – 15
=
58º
14 – 15
=
62º
10 – 15
4.
ADJUST THE FAN SPEED
Figure 20. Checking Indoor Airflow over Evaporator Coil using Delta−T Chart
506601−01
DT)
process using the
INDOOR COIL
TEMPERATURE OF AIR
ENTERING INDOOR COIL ºF
A
T
DROP
19º
AIR FLOW
Measure entering air temperature using dry bulb (A) and wet bulb (B). DT is the intersecting value of A and B in the
Measure the coil's dry bulb entering and leaving air temperatures (A and C). Temperature Drop Formula:
If the difference between the measured T
ºF ACTION
4 INCREASE THE AIRFLOW
−1 (WITHIN +3º RANGE) NO CHANGE
−5 DECREASE THE AIRFLOW
See indoor unit instructions to increase/decrease fan speed.
S
Temperature rise between the return air and supply air
temperatures at the indoor coil blower unit,
S
Measuring voltage supplied to the unit,
S
Measuring amperage being drawn by the heat unit(s).
Then, apply the measurements taken in following formula
to determine CFM:
Amps x Volts x 3.41
CFM =
1.08 x Temperature rise (F)
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
WET−BULB ºF
57 58 59 60 61 62 63 64 65 66 67 68 69 70
AIR FLOW
INDOOR COIL
and the desired DT (T
Drop
Changing air flow affects all temperatures; recheck temperatures to
confirm that the temperature drop and DT are within +3º.
Page 28
DT
B
A
72º
B
64º
DRY BULB
WET BULB
–DT) is within +3º, no adjustment
Drop