Carrier 48NLT - Page 12

Table 4 — Rated Gas Inputs
UNIT 48
NUMBER
OF
ORIFICES
GAS SUPPLY PRESSURE
(in. wg)
MANIFOLD
PRESSURE
(in. wg)
NATURAL GAS
PROPANE*
Natural Propane
Orifice
Drill
Size
Heating
Input
(Btuh)t
Orifice
Drill
Size
Heating
Input
(Btuh)t
Min Max Min Max
Natural
Propane
NLT018,024,030
2 5.0
13.6
11 0
136 35
10.5 44 40,000
55
40,000
NLT036,042; NHT024; NMT030
3 50
13.6 11.0 13,6 3.5
10.5 44 60,000
55
60,000
NLT048,060; NMT036,042; NHT030
4
5.0 13.6
11.0 13.6 3.5
105 44
80,000 55
80,000
NET036,042
4 5.0 136 11 0 13,6
3.5 10.5
42 96,000
54
96,000
NMT048,060; NHT036,042
5 5.0 13.6
11.0 13.6 3.5 10.5
44 100,000
55
100,000
NHT048,060; NVT036,042
6 5.0 13.6 11.0 13.6
35 10.5
44
- - ■ ■ 1
120,000
55
120,000
NVT048,060
6 50 13.6 11.0
136 3.5 10.5
42 , 144,000
54
144,000
*When a 48N unit is converted to propane, the unit must be modified. See kit instructions.
tBased on altitudes from sea level up to 2000 ft above sea level. For altitudes above 2000 ft, reduce
input rating 4% for each 1000 ft above sea level In Canada, from 2000 ft above sea level to 4500 ft
above sea level, derate the unit 10%,
NOTE; All other appliances that use the same meter must
be turned off when gas flow is measured at the meter.
Proceed as follows:
1. Turn off gas supply to unit.
2. Remove pipe plug on outlet of gas valve, then connect
manometer at this point. Turn on gas to unit.
3. Record number of seconds for gas meter test dial to make
one revolution.
4. Divide number of seconds in Step 3 into 3600 (number
of seconds in one hour).
5. Multiply result of Step 4 by the number of cu ft shown
for one revolution of test dial to obtain cu ft of gas flow
per hour.
6. Multiply result of Step 5 by Btu heating value of gas to
obtain total measured input in Btuh. Compare this value
with heating input shown in Table 4. (Consult the local
gas supplier if the heating value of gas is not known.)
Example: Assume that the size of test dial is one cu ft, one
revolution takes 30 seconds, and the heating value of the
gas is 1050 Btu/ft^. Proceed as follows:
1. 30 seconds to complete one revolution.
2. 3600 ^ 30 = 120.
3. 120 X 1 = 120 ft^ of gas flow/hr.
4. 120 X 1050 = 126,000 Btuh input.
If the desired gas input is 125,000 Btuh, only a minor
change in the manifold pressure is required.
Observe manifold pressure and proceed as follows to
adjust gas input:
1. Remove cover screw over regulator adjustment screw
on gas valve.
2. Turn regulator adjustment screw clockwise to increase
gas input, or turn regulator adjustment screw counter¬
clockwise to decrease input. Manifold pressure must be
between 3.2 and 3.8 in. wg.
A WARNING
Unsafe operation of the unit may result if manifold
pressure is outside this range. Personal injury or unit
damage may result.
3. Replace cover screw cap on gas valve.
4. Turn off gas supply to unit. Remove manometer from
pressure tap. Replace pipe plug on gas valve. Turn on
gas to unit. Check for leaks.
Measure Manifold Pressure (Propane Units) — The main
burner orifices on a propane gas unit are sized for the unit
rated input when the manifold pressure is 10.5 in. wg.
Proceed as follows to adjust gas input on a propane gas
unit:
1. Turn off gas to unit.
2. Remove pipe plug on outlet of gas valve, then connect
manometer at this point.
3. Turn on gas to unit.
4. Remove cover screw over regulator adjustment screw
on gas valve.
5. Adjust regulator adjustment screw for a manifold pres¬
sure reading of 10.5 in. wg. Turn adjusting screw clock¬
wise to increase manifold pressure, or turn adjusting screw
counterclockwise to decrease manifold pressure.
6. Replace cover screw.
7. Turn off gas to unit. Remove manometer from pressure
tap. Replace pipe plug on gas valve, then turn on gas to
unit. Check for leaks.
CHECK BURNER FLAME — Observe the unit heating
operation, and watch the burner flames through the obser¬
vation port to see if they are light blue and soft in appear¬
ance, and that the flames are approximately the same for
each burner. See Fig. 11.
BLOWER HEAT-RELAY OPERATION - Blower relay
PCI (see the unit wiring diagram) is located in the control
box and adjusts to permit either longer or shorter “off” cy¬
cles. The “on” cycle is factory set for one minute on tim¬
ing. The adjusting dial on the relay (see Fig. 12) is factory
set at the minimum position to provide optimum perfor¬
mance for most installations. On unusual installations, the
length of time the blower remains on may need to be
increased. To increase blower operation time, rotate the ad¬
justing dial counterclockwise. To decrease blower opera¬
tion time, rotate dial clockwise.
AIRFLOW AND TEMPERATURE RISE - The heating
section for each size unit is designed and approved for heat¬
ing operation within the temperature-rise range stamped on
the unit rating plate.
Table 5 shows the approved temperature-rise range for
each unit, and the air delivery cfm at various temperature
rises. The heating operation airflow must produce a tem¬
perature rise that falls within the approved range.
Refer to Indoor Airflow and Airflow Adjustments sec¬
tion to adjust heating airflow when required.
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