Lennox Merit 14HPX Installation Instructions Manual page 25

CHECKING AIR FLOW AT INDOOR COIL
Cooling Mode Indoor Airflow Check
Check airflow using the Delta−T (
19.
Heating Mode Indoor Airflow Check
Blower airflow (CFM) may be calculated by energizing
electric heat and measuring:
Temp.
80 24 24 24 23 23 22 22 22 20 19 18 17 16 15
of air
entering
78 23 23 23 22 22 21 21 20 19 18 17 16 15 14
indoor
76 22 22 22 21 21 20 19 19 18 17 16 15 14 13
coil ºF
74 21 21 21 20 19 19 18 17 16 16 15 14 13 12
A 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
T
Drop
C
19º
53º
air flow
DRY
BULB
All temperatures are
expressed in ºF
Figure 19. Checking Indoor Airflow over Evaporator Coil using Delta−T Chart
WEIGH IN
Use method for adding initial refrigerant charge, and then use
verifying refrigerant charge.
WEIGH IN
CALCULATING SYSTEM CHARGE FOR OUTDOOR UNIT VOID OF CHARGE
If the system is void of refrigerant, first, locate and repair any leaks and then weigh in the refrigerant charge into the unit. To calculate the total refriger-
ant charge:
Amount specified on
nameplate
DT)
process using figure
DT
B
B
air flow
64º
INDOOR WET
BULB
COIL
CHARGING METHOD
Adjust amount. for variation in line set
length listed on line set length table below.
+
Refrigerant Charge per Line Set Length
LIQUID LINE SET DIAMETER
3/8" (9.5 MM)
*If line length is greater than 15 ft. (4.6 m), add this amount. If line length is less than 15 ft. (4.6 m), subtract this
amount.
NOTE Insulate liquid line when it is routed through areas where the surrounding ambient temperature could
become higher than the temperature of the liquid line or when pressure drop is equal to or greater than 20 psig.
NOTE The above nameplate is for illustration purposes only. Go to actual nameplate on outdoor unit for charge
information.
Figure 20. Weigh In Method
1. Temperature rise between the return air and supply air
temperatures at the indoor coil blower unit,
2. Measuring voltage supplied to the unit,
3. Measuring amperage being drawn by the heat unit(s).
Then, apply the measurements taken in the following
formula to determine CFM:
Amps x Volts x 3.41
CFM =
1.08 x Temperature rise (F)
1. Determine the desired DT Measure entering air temper-
ature using dry bulb (A) and wet bulb (B). DT is the intersect-
ing value of A and B in the table (see triangle).
2. Find temperature drop across coil
bulb entering and leaving air temperatures (A and C). Tem-
perature Drop Formula: (T
3. Determine if fan needs adjustment
the measured T
+3º, no adjustment is needed. See examples: Assume DT =
A
15 and A temp. = 72º, these C temperatures would necessi-
72º
tate stated actions:
T –
Cº
Drop
19 –
53º
DRY
14 –
58º
BULB
10 –
62º
4. Adjust the fan speed
crease/decrease fan speed.
Changing air flow affects all temperatures; recheck tempera-
tures to confirm that the temperature drop and DT are within
+3º.
Additional charge specified per indoor
unit match−ups table.
+
OUNCES PER 5 FEET (G PER 1.5 M) ADJUST FROM 15 FEET (4.6 M)
3 OUNCE PER 5' (85 G PER 1.5 M)
Page 25
Measure the coil's dry
) = A minus C.
Drop
If the difference between
and the desired DT (T
Drop
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 in-
SUBCOOLING
method for
=
LINE SET*
–DT) is within
Drop
Total Charge
14HPX SERIES