IM 178 / Page 9
Table 2. Controls, settings and functions (continued)
SYMBOL
DESCRIPTION
FUNCTION
RESET
LOCATION
SETTING
RANGE
DIFFERENTIAL
PART NO.
SPS6
Dirty filter pressure
Sensors pressure drop across final filter bank and
N/A
Final filter section
N/A
0–5" w.c.
N/A
495450B-05
sensor
sends signal to MicroTech controller.
(0–1245.4 Pa)
1–6 VDC out
S1
System switch
Shuts off entire control circuit (except crankcase
N/A
Main control box
N/A
N/A
N/A
013550B-00
heaters).
TD9, 19
Part winding start
Reduces inrush amp draw on start-up
Auto
Main control box
1 sec., fixed
N/A
N/A
282101D-01
timer (fans)
ZNT1, 2, 3
Space temperature
Senses space temperature; sends signal to
N/A
In building space
N/A
3K ohms at
N/A
See IM 483
sensors
MicroTech controller.
77
°
F (25
°
C)
GAS HEATING CONTROLS
AS
Blower air switch
Proves presence of combustion air.
N/A
Gas furnace control
0.4" w.c., fixed
N/A
N/A
330038B-00
section
FD
Flame rod
Senses pilot flame.
N/A
Gas burner assembly
N/A
N/A
N/A
365577A-00
FLC
Fan control
Closes to energize fan when heat exchanger is warm.
Auto
Gas heating section
Closes at 125
°
F6
5
°
F–220
°
F2
5
°
F (14
°
C)
340821B-00
(52
°
C)
(18
°
C–104
°
C)
adjustable
Opens at 100
°
F5
0
°
F–205
°
F
(28
°
C)
(10
°
C–96
°
C)
High limit cutout
Opens furnace control circuit on temperature rise.
Auto
Gas heating section
Opens at 200
°
F
100
°
F–250
°
F2
5
°
F (14
°
C),
(93
°
C
)
fixed
FSG
Flame safeguard
Proves pilot flame and controls main gas valve.
Manual
Gas furnce control
N/A
N/A
N/A
See IM 684 or 685
section
GV1
Pilot gas valve
Opens to allow flow of gas to pilot burner.
Normally
Gas heating section
N/A
N/A
N/A
344884B-00
closed
GV2, 3
Main gas valves
Open to allow flow of gas to main burner.
Normally
Gas heating section
N/A
N/A
N/A
See IM 684 or 685
closed
HL22
Filter high limit control
Opens furnace control circuit on temperature rise.
Manual
Supply air section
Opens at 125
°
F
N/A
25
°
F (14
°
C),
479388B-01
(52
°
C
)
fixed
HL23
Final filter high limit control
Opens furnace control circuit on temperature rise.
Manual
Final filter section
Opens at 165
°
F
N/A
25
°
F (14
°
C),
479388B-04
(74
°
C
)
fixed
HPR
High pressure regulator
Regulates pressure to main regulator.
N/A
In gas line before MPR
As specified
10"–13" w.c.
N/A
See parts ca
talog
(2491–3238 Pa)
HP5
High gas pressure switch
Shuts off burner if pressure goes above set point.
Manual
Gas heating section
8" w.c. (1993 Pa)
5"–35" w
.c.
1"–3" w.c.
See parts catalog
(1245–8718 Pa)
(249–747
Pa)
LP5
Low gas pressure switch
Shuts off burner if pressure goes below set point.
Auto
Gas heating section
4" w.c. (996 Pa)
3"–21" w.c.
1
"–3" w.c.
See parts catalog
(747–5231 Pa)
(249–747 Pa)
ELECTRIC HEATING CONTROLS
HL1, 4 &
Secondary heater limit
Breaks line voltage to heaters if temperatures are too
Manual
Electric heat section
Cutout=210
°
F
N/A
N/A
654962B-01
HL11-14
control
high.
(99
°
C)
HL31-34 &
Primary heater limit control
Breaks control voltage to heat contactor if
Auto
Electric heat section
Cutout=175
°
F
N/A
30
°
F (16
°
C)
658245B-01
HL41-44
heater temperatures are too high.
(79
°
C
)
fixed
Cutin=145
°
F
(63
°
C)
HS1
Switch (toggle),
Shuts off electric control circuit manually.
N/A
Main control box
N/A
N/A
N/A
237803D-01
electric heat
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