Lennox XC21 Series Unit Information 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.
This unit is NOT approved for use with coils which use capillary tubes or fixed orifices as a refrigerant metering device.
Check airflow using the Delta−T (
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
is the intersecting value of A and B in the table (see triangle).
2. Find temperature drop across coil
(A and C). Temperature Drop Formula: (T
3. Determine if fan needs adjustment
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
Figure 14. Checking Indoor Airflow over Evaporator Coil using Delta−T Chart
XC21
DT)
process using the illustration in Figure 14.
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
Measure the coil's dry bulb entering and leaving air temperatures
) = A minus C.
Drop
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.
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
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
and the desired
Drop