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AIR CONDITIONING AIRFLOW 070 MODEL 090 MODEL 110, 135,
TONS (12,000 BTU/HR) (CFM) & 155 MODELS
1-1/2 525 X X
2 700 X X X
2-1/2 875 X X X
3 1050 X X X
3-1/2 1225 X X X
4 1400 X X
5 1750 X
6 2100 X
X-INDICATES AN ALLOWABLE SELECTION.
AIR CONDITIONING (A/C) OR CONTINUOUS-FAN (CF) AIRFLOW SELECTION CHART
BASED ON 350 CFM/TON
SW1-5 OFF
MODEL
SIZE
070 DEF 525
2
700 875 1050
1
1225 1225 1225
090 DEF 525 700
2
875 1050 1225 1400
1
1400
110,135,155 DEF 700 875
2
1050 1225 1400 1750
1
2100
2
1
2
1
1
2
SWITCH SW3 POSITIONS
1.DEFAULT A/C AIRFLOW WHEN A/C SWITCHES ARE IN OFF POSITION (FACTORY SETTING)
2.DEFAULT CONT. FAN AIRFLOW WHEN CF SWITCHES ARE IN OFF POSITION (FACTORY SETTING)
3. SWITCH POSITIONS ARE ALSO SHOWN ON FURNACE WIRING DIAGRAM
BASED ON 400 CFM/TON
SW1-5 ON
MODEL
SIZE
070 DEF 600
2
800 1000 1200
1
1400 1400 1400
090 DEF 600 800
2
1000 1200 1400 1600
1
1600
110,135,155 DEF 800 1000
2
1200 1400 1600 2000
1
2200
SWITCH SW3 POSITIONS
OFF
321
OFF
321
OFF
321
OFF
321
OFF
321
OFF
321
OFF
321
OFF
321
OFF
321
OFF
321
OFF
321
OFF
321
OFF
321
OFF
321
OFF
321
OFF
321
COOLING TONNAGE VS. AIRFLOW (CFM)
A08470
Fig. 57 -- Cooling (A/C) or Continuous--Fan (CF) Airflow Selection Chart
The furnace will start up in either low-- or high--heat. If the
furnace starts up in low--heat, the control CPU determines the
low--heat on--time (from 0 to 16 minutes) which is permitted
before switching to high--heat.
If the power is interrupted, the stored history is erased and the
control CPU will select low--heat for up to 16 minutes and then
switch to high--heat, as long as the thermostat continues to call for
heat. Subsequent selection is based on stored history of the
thermostat cycle times.
The wall thermostat “calls for heat”, closing the R--to--W circuit.
The furnace control performs a self--check, verifies the low--heat
and high--heat pressure switch contacts LPS and HPS are open,
and starts the inducer motor IDM in high--speed.
a. Inducer Prepurge Period
(1.) If the furnace control CPU selects low--heat oper-
ation the inducer motor IDM comes up to speed,
the low--heat pressure switch LPS closes, and the
furnace control CPU begins a 15--second prepur-
ge period. If the low--heat pressure switch LPS
fails to remain closed the inducer motor IDM will
remain running at high--speed. After the low--heat
pressure switch re--closes the furnace control CPU
will begin a 15--second prepurge period, and con-
tinue to run the inducer motor IDM at high--
speed.
(2.) If the furnace control CPU selects high--heat op-
eration, the inducer motor IDM remains running
at high--speed, and the high--heat pressure switch
relay HPSR is de--energized to close the NC con-
tact. When sufficient pressure is available the
high--heat pressure switch HPS closes, and the
high--heat gas valve solenoid GV--HI is ener-
gized. The furnace control CPU begins a
15--second prepurge period after the low--heat
pressure switch LPS closes. If the high--heat pres-
sure switch HPS fails to close and the low--heat
pressure switch LPS closes, the furnace will oper-
ate at low--heat gas flow rate until the high--heat
pressure switch closes for a maximum of 2 min-
utes after ignition.
b. Igniter Warm--Up --At the end of the prepurge period,
the Hot--Surface Igniter HSI is energized for a
17--second igniter warm--up period.
c. Trial--For--Ignition Sequence --When the igniter
warm--up period is completed the main gas valve relay
contact GVR closes to energize the gas valve solenoid
GV--M. The gas valve solenoid GV--M permits gas
flow to the burners where it is ignited by the HSI. Five
315AAV