Lennox Merit 13HPX Series Installation Instructions Manual page 26

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
USE
COOLING
MODE
60ºF
(15ºC)
USE
HEATING
MODE
SATº
LIQº –
SCº =
Figure 23. Using HFC−410A Subcooling Method
506727−01
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DT
B
B
air flow
64º
INDOOR
COIL
Figure 22. Checking Airflow over Indoor Coil Using Delta−T Formula
1. Check liquid and vapor line pressures. Compare pressures with either second−stage heat or cooling mode
normal operating pressures listed in table 4. Table 4 is a general guide and expect minor pressures
variations. Significant pressure differences may indicate improper charge or other system problem.
2. Decide whether to use cooling or heating mode based on current outdoor ambient temperature:
Use COOLING MODE
A
S
Outdoor ambient temperature is 60°F (15.5°C) and above.
S
Indoor return air temperature range is between 70 to 80°F (21−27°C). This temperature range is
what the target subcooling values are base upon in table 3.
If indoor return air temperature is not within reference range, set thermostat to cooling mode and a
setpoint of 68ºF (20ºC). This should place the outdoor unit into second−stage (high−capacity) cooling
mode. When operating and temperature pressures have stabilized, continue to step 3.
Use HEATING MODE
B
S
Outdoor ambient temperature is 59°F (15.0°C) and below.
S
Indoor return air temperature range is between 65−75°F (18−24°C). This temperature range is
what the target subcooling values are base upon in table 3.
If indoor return air temperature is not within reference range, set thermostat to heating mode and a
setpoint of 77ºF (25ºC). This should place the outdoor unit into second−stage (high−capacity) heating
mode. When operating and temperature pressures have stabilized, continue to step 3.
3. Read the liquid line pressure; then find its corresponding temperature pressure listed in table 5 and record
it in the SATº space to the left.
4. Read the liquid line temperature; record in the LIQº space to the left.
5. Subtract LIQº temperature from SATº temperature to determine subcooling; record it in SCº space to the
left..
6. Compare SCº results with table 3 (either Heating or Cooling mode column), also consider any additional
charge required for line set lengths longer than 15 feet and/or unit matched component combinations (Add
Charge column).
7. If subcooling value is:
AGREATER than shown for the applicable unit match component, REMOVE refrigerant;
BLESS than shown for the applicable unit match component, ADD refrigerant.
8. If refrigerant is added or removed, repeat steps 3 through 6 to verify charge.
9. Close all manifold gauge set valves and disconnect gauge set from outdoor unit.
10. Replace the stem and service port caps and tighten as specified in Operating Service Valves on page 2.
11. Recheck voltage while the unit is running. Power must be within range shown on the nameplate.
search engine
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
WET
4. Adjust the fan speed
BULB
crease/decrease fan speed.
Changing air flow affects all temperatures; recheck tempera-
tures to confirm that the temperature drop and DT are within
+3º.
when:
when:
Second Stage (High Capacity)
Page 26
Measure the coil's dry
) = A minus C.
Drop
If the difference between
and the desired DT (T
Drop 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-
Optimizing Charge
–DT) is within