Carrier 58MXA Installation, Start-Up, And Operating Instructions Manual page 45

Fig. 58—Orifice Holes
BURNER FLAME
MANIFOLD
Fig. 59—Burner Flame
EXAMPLE:
100,000 Btuh input furnace installed at 4300 ft.
Derate
Furnace Input Rate X Multiplier
at Sea Level Factor
100,000 X
Table 11–Altitude Derate Multipler for U.S.A.
ALTITUDE PERCENT
(FT) OF DERATE
0–2000 0
2001–3000 4–6
3001–4000 6–8
4001–5000 8–10
5001–6000 10–12
6001–7000 12–14
7001–8000 14–16
8001–9000 16–18
9001–10,000 18–20
* Derate multiplier factor is based on midpoint altitude for altitude range.
BURNER
ORIFICE
A93059
BURNER
A89020
Furnace Input Rate
= at Installation
Altitude
0.91 = 91,000
DERATE MULTIPLIER
FACTOR*
1.00
0.95
0.93
0.91
0.89
0.87
0.85
0.83
0.81
EXAMPLE: (0-2000 ft altitude)
Furnace input from rating plate is 100,000 Btuh.
Btu heating input = Btu/cu ft X cu ft/hr
Heating value of gas = 975 Btu/cu ft
Time for 1 revolution of 2-cu ft dial = 70 sec
Gas rate = 103 cu ft/hr (from Table 12)
Btu heating input = 103 X 975 = 100,425 Btuh. In this
example, the orifice size and manifold pressure adjustment
is within ±2 percent of the furnace input rate.
SET TEMPERATURE RISE
Temperature rise must be within limits specified on unit
rating plate. Recommended operation is at midpoint of rise or
slightly above. Failure to follow this caution may result in
condensing or overheating the heat exchangers.
Determine and adjust air temperature rise as follows:
1. Place thermometers in return and supply ducts as close to
furnace as possible. Be sure thermometers do not see heat
exchanger so that radiant heat does not affect readings. This
practice is particularly important with straight-run ducts.
2. When thermometer dings stabilize, subtract return-air tem-
perature from supply-air temperature to determine air tem-
perature rise.
3. Adjust temperature rise by adjusting blower speed. Increase
blower speed to reduce temperature rise. Decrease blower
speed to increase temperature rise.
Disconnect 115-v electrical power before changing speed tap.
Failure to follow this warning could result in personal injury.
4. To change blower motor speed selections for heating mode,
remove blower motor lead from control center HEAT termi-
nal. (See Fig. 31.) Select desired blower motor speed lead
from 1 of the other terminals and relocate it to HEAT terminal.
See Table 13 for lead color identification. Reconnect original
lead on SPARE terminal.
Follow this same procedure for proper selection of COOL
speed selection.
→
ADJUST BLOWER OFF DELAY (HEAT MODE)
The blower off delay has 4 adjustable settings from 90 sec to 180
sec. (See Table 14.) The blower off delay jumpers are located on
the furnace control board (see Fig. 31). To change the blower off
delay setting, move the jumper from one set of pins on the control
board to the pins used for the desired blower off delay. Factory
blower off delay setting is 120 sec.
Table 14—Blower Off Delay Setup Position
PINS 1 AND 2
Time (in sec) 90
SET THERMOSTAT HEAT ANTICIPATOR
Thermostat heat anticipator must be set to match amp draw of
components in R-W circuit. Accurate amp draw measurements can
be obtained at thermostat subbase terminals R and W.
Fig. 60 illustrates an easy method of obtaining these measure-
ments. Amp reading should be taken after blower motor has
45
2 AND 3 3 AND 4 4 AND 5
120 150 180