Lennox International Inc Merit Series 14ACX Units Approach Or, Weigh-In, Superheat, Subcooling

3. Determine if fan needs adjustment

CHECKING AIR FLOW AT INDOOR COIL

Check airflow using the Delta−T (DT) process using the illustration in figure 19.

Temp. of air entering indoor coil ºF

A

Dry−bulb

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

1. Determine the desired DT

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: (TDrop) = A minus C.

Wet−bulb ºF 57 58 59 60 61 62 63 64 65 66 67 68 69 70

ference between

		B
C	TDrop
53º	19º
	air flow	air flow	B
DRY			64º
BULB
All temperatures are		INDOOR
		COIL
expressed in ºF

A

72º

DRY

BULB

WET

BULB

the measured TDrop and the desired DT (TDrop–DT) is within +3º, no adjustment is needed. See examples: Assume DT =

15 and A temp. = 72º, these C temperatures would necessi- tate stated actions:

Cº	TDrop	–	DT	=	ºF	ACTION
53º	19	–	15	=	4	Increase the airflow
58º	14	–	15	=	−1	(within +3º range) no change
62º	10	–	15	=	−5	Decrease the airflow

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.

Figure 19. Checking Indoor Airflow over Evaporator Coil using Delta−T Chart

START: Determine how refrigerant is metered

WHEN TO CHARGE?

SBest during warm weather

SCan charge in colder weather by determining best charge method? Determine by:

A Metering device type

B Outdoor ambient temperature

REQUIREMENTS:

SSufficient heat load in structure

SIndoor temperature between 70-80ºF (21−26ºC)

SManifold gauge set connected to unit

SThermometers:

−to measure outdoor ambient temperature

−to measure liquid line temperature

−to measure suction line temperature

Which

metering device?

TXV		RFC
65ºF	64ºF	40ºF	39ºF
(18.3ºC) and	(17.7ºC) and	(4.4ºC) and	(3.8ºC) and
Above	Below	Above	Below
APPROACH OR	WEIGH-IN	SUPERHEAT	WEIGH-IN
SUBCOOLING

Figure 20. Determining Charge Method

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14ACX SERIES