40. Remove blower access panel from front of unit and reinstall
on rear of unit. Reinstall rear blower panel on front of unit.
Reinstall top of unit. Install patch plates on front center panel
and seal all remaining holes as necessary.
41. Reconnect wiring to blower motor, gas valve, pressure
switches, and limit switches using unit wiring diagram. (See
Fig. 17.) Ensure all wiring is properly connected and tight.
NOTE:
Upon completing the installation, pressure test the fur-
nace (using the following procedure) as critical gaskets/seals have
been broken.
PRESSURE TEST
Do not place the unit into operation without checking the
system pressures of the unit as outlined in this procedure.
Failure to follow the pressure test procedure may result in a
non- operational unit, nuisance tripping and/or a condition
which may lead to personal injury.
1. Check wiring to insure it is properly connected and tight.
2. Place a jumper wire across pressure switches to bypass both
controls.
3. Turn gas valve off.
4. Set room thermostat above room temperature.
5. Turn on electrical supply to furnace.
6. Check pressures at:
a. Induced-draft motor tap (located at top left of motor
casing).
b. Tube previously labelled "top of coil."
c. Tube previously labelled "bottom of coil."
Excessive variation of the pressures listed in Table 7 indicates
a system leak and/or blockage. This is especially true of the
induced-draft motor pressure. An induced-draft motor pres-
sure in the 1.5-in. to 1.6-in. wc range of vacuum pressure
indicates a leak in the system and/or excessive vent length.
Corrective action must be taken before the unit is placed into
operation. Failure to take corrective action may result in a
non-operational unit, condensate leakage, nuisance tripping,
premature unit failure, and/or a condition which may lead to
personal injury.
7. Use Table 7 to verify a properly-sealed unit.
NOTE:
The pressures listed are for an ambient temperature of
approximately 76°F. These pressures may vary slightly due to
temperature, vent configuration, and vent length. The table is a
general guideline of system pressures and may vary slightly from
unit to unit.
Table 7—Unit Pressures (In. wc)
UNIT SIZE/
VENTING
INDUCED-DRAFT
MOTOR
PRESSURE
TOP OF COIL
PRESSURE
BOTTOM OF
COIL
PRESSURE
50/Min Vent
Max Vent
2.5
2.5
0.32
0.32
0.94
0.94
75/Min Vent
Max Vent
2.5
2.0
0.37
0.58
1.45
1.50
100/Min Vent
Max Vent
2.4
2.2
0.23
0.29
1.50
1.50
125/Min Vent
Max Vent
2.5
2.3
0.28
0.38
1.60
1.70
8. Reconnect pressure switch tubing as shown in Fig. 13.
9. Turn off electrical supply to unit.
10. Remove jumper wire on pressure switches.
11. Turn on gas valve.
12. Turn on electrical supply to unit. Unit should begin ignition
cycle.
Step 11—Start-up, Adjustment, and Safety Check
GENERAL — The furnace must have a 115-v power supply
properly connected and grounded. Proper polarity must be main-
tained for correct operation. Thermostat wire connections at R, W,
Y, G, and C must be made at the 24-v terminal block on the control
board. The gas service pressure must not exceed 0.5 psig (14-in.
wc), but must be no less than 0.16 psig (4.5-in. wc) for natural gas.
The unit must not be installed, operated, and then turned off
and left turned off in an unoccupied structure during cold
weather when the temperature drops to 32°F and below.
Freezing condensate left in the furnace will damage the
equipment. See Service and Maintenance Instructions for
winterizing procedure.
SEQUENCE OF OPERATION — Using the schematic diagram in
Fig. 17, follow the sequence of operation through the different
modes. This furnace has a unique control system—read and follow
the wiring diagram very carefully.
1. When thermostat "calls for heat", the R-W circuit closes.
a. Ignition sequence—Power from the transformer energizes
the fan control board. The fan control energizes the
induced-draft blower motor. Pressure switches P1 and P2
normally open contacts close to initiate the ignition se-
quence.
b. Ignition trial—The ignition control energizes the pilot gas
valve. The ignition electrode begins sparking to light the
pilot. When the pilot flame is sensed, the main gas valve
opens and the pilot flame lights the burners. If the pilot
flame is not sensed, the ignition control locks out after 90
sec. Reset the ignition control by turning the thermostat
below room temperature for 1 minute and then above room
temperature.
c. Blower on delay— The fan control starts the blower after
30 sec. The blower on delay is not adjustable.
d. Blower off delay—When the thermostat is satisfied, the
circuit between R and W is broken, de-energizing the gas
valve and stopping gas flow to the burners. The blower
motor remains energized 60, 90, 120, or 150 sec depending
on the blower off delay selection (factory shipped set for
60-sec delay).
2. Cooling mode.
The thermostat "calls for cooling" closing R and R-Y circuits.
The R-Y circuit starts the outdoor condensing unit, and the
combined R-Y and R-G circuit starts the furnace blower motor
on cooling speed. The (EAC) terminals are energized with
115v whenever the blower is operating.
When the thermostat is satisfied, the R and R-Y circuits are
broken. The furnace blower will continue operating on cooling
speed for an additional 90 sec.
START-UP PROCEDURES
1. Fill condensate trap with water.
a. Disconnect condensate drain tube from bottom of inducer
housing.
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