Lennox Signature XP21 Series Installation And Service Procedure 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.
COOLING MODE INDOOR AIRFLOW CHECK
Check airflow using the Delta−T (
lustration in figure 16.
HEATING MODE INDOOR AIRFLOW CHECK
Blower airflow cubic feet per minute (CFM) may be calcula-
ted 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
OF A AND B IN THE TABLE (SEE TRIANGLE).
2. FIND TEMPERATURE DROP ACROSS COIL
TURE DROP FORMULA: (T
3. DETERMINE IF FAN NEEDS ADJUSTMENT
NO 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 16. Checking Indoor Airflow over Evaporator Coil using Delta−T Chart
DT)
process using the il-
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
MEASURE THE COIL'S DRY BULB ENTERING AND LEAVING AIR TEMPERATURES (A AND C). TEMPERA-
) = 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.
D Temperature rise between the return air and supply air
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
AIR FLOW
INDOOR COIL
DROP
CHANGING AIR FLOW AFFECTS ALL TEMPERATURES; RECHECK
TEMPERATURES TO CONFIRM THAT THE TEMPERATURE DROP AND
DT ARE WITHIN +3º.
Page 27
DT
B
B
64º
WET BULB
AND THE DESIRED DT (T
–DT) IS WITHIN +3º,
DROP
A
72º
DRY BULB
XP21