Lennox XP17-024-230-01 Installation And Service Procedure page 77

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 48.
HEATING MODE INDOOR AIRFLOW CHECK
Blower airflow (CFM) may be calculated by energizing
electric heat and measuring:
AIRFLOW
INDOOR COIL
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 — 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
3. Determine if fan needs adjustment — If the difference between the measured T
DT (T
–DT) is within +3º, no adjustment is needed. See example below:
Drop
Assume DT = 15 and A temp. = 72º, these C temperatures would necessitate stated actions:
DT
T –
Cº
Drop
19 – 15
53º
14 – 15
58º
10 – 15
62º
4. Adjust the fan speed — See indoor unit instructions to increase/decrease fan speed.
Figure 48. Checking Indoor Airflow over Evaporator Coil using Delta-T Chart
XP17
DT)
process using the
Temperature of air
entering indoor
coil ºF
A
T
Drop
19º
air flow
Drop
=
ºF ACTION
=
4 Increase the airflow
=
-1 (within +3º range) no change
=
-5 Decrease the airflow
Temperature rise between the return air and supply air
D
temperatures at the indoor coil blower unit,
Measuring voltage supplied to the unit,
D
Measuring amperage being drawn by the heat unit(s).
D
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
INDOOR COIL
) = A minus C.
Changing air flow affects all temperatures; recheck
temperatures to confirm that the temperature drop
and DT are within +3º.
Page 77
DT
B
air flow
B
64º
WET BULB
and the desired
Drop
A
72º
DRY BULB