CONQUEST 80 - High Limit Control; High Limit Settings

TABLE 28
HIGH LIMIT SETTINGS
UPFLOWONLY(·GOG, ·GDJ} INPUT
OPEN
RESET
04(-)AU 45,000
160° 140°
05(-)AU
50,000
150° 130°
06(-)AU 67,500
170°
150°
07(-)AM 75,000
160° 140°
07(-)AU
75,000
170°
150°
10(-)AM/AU 100,000
170°
150°
10(-)BR 100,000
160°
140°
12(-)AR 125,000
150°
130°
15(-)AR 150,000
150°
130°
UPFLOWL!:!ORIZONTALl·GPH, -GPJ}
INPUT
OPEN RESET
04(-)AU 45,000
160° 140°
05(-)AU 50,000
150° 130°
06(-)AU 67,500
170° 150°
07(-)AM 75,000
160° 140°
07(-)AU
75,000 170° 150°
10(-)AM 100,000
170° 150°
10(-)BR
100,000
160°
140°
12(-)AR 125,000
150° 130°
15(-)AR 150,000
150° 130°
DOWNFLOWONLY(·GLH, -GLJ} INPUT
OPEN RESET
04(-)AU 45,000
230° 210°
05(-)AU 50,000
220°
200°
06(-)AU 67,500
210° 190°
07(-)AM
75,000 200° 180°
07(-)AU 75,000
200° 180°
10(-)AM
100,000
200° 180°
10(-)AU 100,000
220° 200°
10(-)BR 100,000
220°
200°
12(-)AR 125,000 200° 180°
15(-)AR 150,000
200° 180°
DOWNFLOWl!:!ORIZONTAL{·GLG} INPUT
OPEN RESET
05(-)AU 50,000
220°
200°
07(-)AM
75,000 200° 180°
07(-)AU 75,000
200°
180°
10(-)AU 100,000
220°
200°
10(-)BR 100,000
220°
200°
12(-)AR
125,000
200° 180°
15(-)AR
150,000
200° 180°
DEDICATEDHORIZONTAL(·GVG, ·GVH} INPUT
OPEN
RESET
04(-)AU 45,000
160°
140°
05(-)AU 50,000
150°
130°
06(-)AU 67,500
170°
150°
07(-)AM 75,000
160°
140°
07(-)AU 75,000
170°
150°
10(-)AM
100,000
170°
150°
10(-)BR
100,000
160°
140°
12(-)AR
125,000
150°
130°
15(-)AR 150,000 150° 130°
There are several reasons for a limit
5,
A problem affecting the main
switch to open and almost always
blower:
involve low air flow through the
A, A wrong speed tap selection.
furnace.
B, Failing motor bearings,
1,
A dirty or restricted air filter,
C. Low voltage to the motor.
2,
A dirty or restricted cooling coil.
0, Dirty blower wheel.
3,
Undersized or restricted return
E, Wrong motor rotation,
air system.
F, Blower wheel slipping on the
4. Undersized or restricted supply
motor shaft.
air system, 6.
Overtiring the furnace with too
much gas pressure,
HIGH LIMIT CONTROL
Operation. All furnace models use
a high limit control. It detects
abnormally high air temperatures in
the heat exchanger area and
prevents the air leaving the furnace
from exceeding the maximum outlet
air temperature. If it opens it shuts
down the burners and runs both the
main blower and the induced draft
blower, It resets automatically after
the air temperature drops, The high
limit is set at the factory and cannot
be field adjusted,
Check. Use an Ohmmeter to check
for an open limit.
1. Turn off all power to the furnace.
2,
Disconnect a wire from one of
the limit terminals.
3,
Measure the Ohm resistance
across the limit contacts.
4,
A zero Ohm reading indicates a
closed limit switch.
5,
If the resistance is infinite, the
limit is open.
The limit can be checked with power
on using a volt meter, A voltage
reading indicates an open switch,
A zero volt reading confirms a
closed switch.
If the limit is open, the main blower
should be operating, cooling the limit
switch, Allow the unit time to reset
the limit.
FIGURE 94
HIGH LIMIT CONTROL
fl"
90