Lennox Signature XC17 Installation Instructions Manual page 27

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
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:
T
Cº
Drop
19 –
53º
14 –
58º
10 –
62º
4. Adjust the fan speed
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DT)
process using the illustration in Figure 12.
Temperature of air
entering indoor
coil ºF
A
DRY
BULB
T
Drop
C
53º
19º
All temperatures are expressed in ºF
Measure entering air temperature using dry bulb (A) and wet bulb (B). DT
DT =
– ºF ACTION
=
15 4 Increase the airflow
=
15 −1 (within +3º range) no change
=
15 −5 Decrease the airflow
See indoor unit instructions to increase/decrease fan speed.
Figure 12. Checking Indoor Airflow over Evaporator Coil using Delta−T Chart
search engine
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
Wet−bulb ºF 57 58 59 60 61 62 63 64 65 66 67 68 69 70
air flow
Measure the coil's dry bulb entering and leaving air temperatures
) = A minus C.
Drop
If the difference between the measured T
Changing air flow affects all temperatures; recheck
temperatures to confirm that the temperature drop
and DT are within +3º.
Page 27
B
air flow
B
64º
INDOOR COIL
and the desired
Drop
A
72º
DRY BULB
WET BULB
XC17 SERIES