202
ing 5 seconds, and then turning back up to call for heat. Controls
will automatically reset after one hour and initiate a call for heat.
Manifold Pressure Adjustment (Duct and Rack System Fur
-
naces) — A pressure tap is provided in each furnace manifold for
measuring the gas manifold pressure. Manifold pressure must be
checked at start-up and during any service or maintenance. All
control systems require a manifold pressure of 3.40 to 3.50 in. wg
at maximum input rating on natural gas, and 10.0 in. wg on pro
-
pane gas at maximum input rating. See Fig. 150-152 on page 186
for gas valve adjustment locations.
NOTE: For two-stage and modulating control applications, verify
proper low fire adjustments as outlined in the Sequence of Opera
-
tion document provided in the instruction package. Check the fur
-
nace section for this document or contact your Carrier service
representative.
Burner Flames (Duct and Rack System Furnaces) — Before
completing the start-up, check the appearance of the main burner
flame.
1. The burner flame should be predominately blue in color, and
well-defined and centered at the tube entry as shown in
Fig. 180. Distorted flame or yellow tipping of natural gas
flame, or a long yellow flame on propane, may be caused by
lint and dirt accumulation inside burner or at burner ports, at
air inlet between burner and manifold pipe, or debris in the
main burner orifice. Soft brush or vacuum clean affected ar
-
eas.
2. Poorly defined, unfocused, substantially yellow flames, or
flames that appear weak or wavering, indicate poor air sup
-
ply to burners or excessive burner input. Verify gas supply
type and manifold pressure with rating plate.
Poor air supply can be caused by obstructions or blockage in heat
exchanger tubes or vent discharge pipe. Inspect and clean as nec
-
essary to eliminate blockage. Vacuum any dirt or loose debris.
Clean heat exchanger tubes with stiff brush.
Poor flame characteristics can also be caused by undersized com
-
bustion air openings or flue gas recirculation into combustion air
supply. Increase air opening size or re-direct flue products to pre
-
vent re-circulation.
Reduced air delivery can also be the result of fan blade slippage,
dirt accumulation on the fan blade, or low voltage to draft inducer
motor. Inspect draft fan assembly and be sure fan blade is secure
to motor shaft. Check line voltage to heater.
Normal Operation (Duct and Rack System Furnaces)
1. Turn on electrical supply to unit at disconnect switch.
2. Turn on manual gas supply.
3. Set thermostat or temperature controller to desired tempera
-
ture.
Information outlining the normal sequence of operation and wir
-
ing diagram for the control system supplied with the furnace mod
-
el is located in the furnace section, or contact your Carrier service
representative.
Shutdown (Duct and Rack System Furnaces)
1. Set thermostat or controller to lowest setting.
2. Turn off electrical supply to unit at disconnect switch.
3. Turn off manual gas supply.
4. Disconnect manifold and inlet pressure taps and re-install
pipe plugs.
5. Replace vestibule access panel or close door.
Energy Recovery Wheel
1. By hand, turn the wheel clockwise (as viewed from the
pulley side), to verify that the wheel turns freely through a
full 360-degree rotation.
2. Before applying power to the drive motor, confirm that
the wheel segments are fully engaged in the wheel frame
and that the segment retainers are completely fastened.
(See Fig. 181.)
3. With hands and objects away from moving parts, activate
the unit and confirm wheel rotation. The wheel rotates
clockwise (as viewed from the pulley side).
4. If the wheel has difficulty starting, turn the power off and
inspect for excessive interference between the wheel sur
-
face and each of the four (4) diameter seals. To correct,
loosen the diameter seal adjusting screws and back ad
-
justable diameter seals away from the surface of the
wheel, apply power to confirm that the wheel is free to ro
-
tate, then re-adjust and tighten the hub and diameter seals
according to the instructions in the Service section.
5. Start and stop the wheel several times to confirm seal ad
-
justment and to confirm that the belt is tracking properly
on the wheel rim (approximately
1
/
4
in. from outer edge of
rim).
ZEROING THE MINIHELIC GAGE BEFORE START UP
If the Minihelic
1
gage needs to be removed or replaced, after in
-
stallation, it may need to be zeroed before placing in operation. If
re-zeroing is required, firmly hold the case of gage with one hand
and unscrew the front cover with the palm of the other hand in a
counterclockwise direction. If difficult to loosen, place a small
sheet of rubber between the cover and the palm of the hand. Zero-
adjust screw is located behind the scale at the pair marked “zero.”
Use a hex/allen wrench and adjust until pointer is on zero. This
must be done with both pressure connections vented to atmo
-
sphere and the gage oriented in the final mounting position. Re
-
place cover.
Fig. 180 —
Proper Flame Appearance
A48-
CAUTION
Keep hands away from rotating wheel. Contact with rotat
-
ing wheel can cause physical injury.
1. Minihelic is a registered trademark of Dwyer Instruments Inc.
WHEEL RIM
S
EGMENT
RETAINER
CATCH
PU
S
H
TOWARD
CENTER
S
POKE
CENTER OF
WHEEL
ROTATE AWAY
FROM WHEEL RIM
2
1
Fig. 181 —
Segment Retainer
a39-2379
