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INLET
PRESSURE TAP
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Fig. 55—Redundant Automatic Gas Control Valve
Fig. 56—Orifice Holes
BURNER FLAME
MANIFOLD
Fig. 57—Burner Flame
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
exchangers so that radiant heat does not affect readings.
This practice is particularly important with straight-run
ducts.
2. When thermometer readings stabilize, subtract return-air
temperature from supply-air temperature to determine air
temperature rise.
ON AND
OFF SWITCH
GAS
PRESSURE
REGULATOR
ADJUSTMENT
BURNER
ENCLOSURE
REFERENCE
PRESSURE
TAP
MANIFOLD
PRESSURE TAP
A95622
BURNER
ORIFICE
A93059
BURNER
A89020
—55—
TABLE 15–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 factors are based on midpoint altitude for altitude range.
3. Adjust temperature rise by adjusting blower speed. Increase
blower speed to reduce temperature rise. Decrease blower
speed to increase temperature rise.
WARNING: ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal
injury or death.
Disconnect 115-v electrical power before changing speed
tap.
4. To change blower motor speed selections for heating mode,
remove blower motor lead from control HEAT terminal.
(See Fig. 36.) Select desired blower motor speed lead from
1 of the other motor leads and relocate it to HEAT terminal.
See Table 17 for lead color identification. Reconnect
original lead on SPARE terminal.
Follow this same procedure for proper selection of COOL
speed selection.
C. Adjust Blower Off Delay (Heat Mode)
The blower off delay has 4 adjustable settings from 90 sec to 180
sec. (See Table 18.) The blower off delay jumpers are located on
the furnace control (See Fig. 31). To change the blower off delay
setting, move the jumper from one set of pins on the control to the
pins used for the desired blower off delay. Factory blower off
delay setting is 120 sec.
D. Set Thermostat Heat Anticipator
When using a nonelectronic thermostat, the thermostat heat
anticipator must be set to match the amp draw of the electrical
components in R-W circuit. Accurate amp draw readings can be
obtained at thermostat subbase terminals R and W. Fig. 58
illustrates the easy method of obtaining actual amp draw. The amp
reading should be taken after blower motor has started and furnace
is heating. Connect ammeter wires as shown in Fig. 58. The
thermostat anticipator should NOT be in the curcuit while mea-
suring current. If thermostat has no subbase, the thermostat must
be disconnected from R and W wires during current measurement.
See thermostat manufacturer's instructions for adjusting heat
anticipator and for varying heating cycle length.
For an electronic thermostat, set cycle rate for 3 cycles per hour.
VI. CHECK SAFETY CONTROLS
This section covers the safety controls that must be checked before
the installation is complete. The flame sensor, gas valve, and
pressure switch were all checked in the Start-up procedure section
as part of normal operation.
A. Check Primary Limit Control
This control shuts off gas control system and energizes air-
circulating blower motor if furnace overheats. Recommended
method of checking this limit control is to gradually block off
return air after furnace has been operating for a period of at least
5 minutes. As soon as limit control has shut off burners, return-air
opening should be unblocked to permit normal air circulation. By
using this method to check limit control, it can be established that
limit is functioning properly and operates if there is a restricted
return-air duct or motor failure. If limit control does not function
during this test, cause must be determined and corrected.
DERATE MULTIPLIER
FACTOR*
1.00
0.95
0.93
0.91
0.89
0.87
0.85
0.83
0.81
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