FURNACE OVERHEATING HAZARD
Failure to follow this caution may result in reduced furnace
life.
Recheck temperature rise. It must be within limits specified
on the rating plate. Recommended operation is at the mid-
point of rise range or slightly above
6. Set thermostat heat anticipator.
a. Mechanical thermostat—Set thermostat heat anticipator to
match the amp draw of the electrical components in the
R-W circuit. Accurate amp draw readings can be obtained
at the wires normally connected to thermostat subbase
terminals, R and W. The thermostat anticipator should
NOT be in the circuit while measuring current.
(1.) Remove thermostat from subbase or from wall.
(2.) Connect an amp meter as shown in Fig. 48 across the
R and W subbase terminals or R and W wires at wall.
(3.) Record amp draw across terminals when furnace is in
heating and after blower starts.
(4.) Set heat anticipator on thermostat per thermostat
instructions and install on subbase or wall.
b. Electronic thermostat: Set cycle rate for 4 cycles per hr.
7. Adjust blower off delay
The blower off delay has 4 adjustable settings from 90 sec to
180 sec. The blower off delay jumpers are located on the
furnace control board. (See Fig. 24.)
To change the blower off delay setting, move the jumper from
one set of pins on the control to the pins used for the selected
blower off delay. Factory off delay setting is 120 sec.
8. Set airflow CFM for cooling
Select the desired blower motor speed lead for cooling
airflow. See Table 5-Air Delivery-CFM (With Filter). See
Table 9 for lead color identification.
Step 4—Check Safety Controls
The flame sensor, gas valve, and pressure switch were all checked
in the Start-up procedure section as part of normal operation.
1. Check Main Limit Switch(es)
This control shuts off combustion control system and ener-
gizes air-circulating blower motor, if furnace overheats. By
using this method to check limit control, it can be established
that limit is functioning properly and will operate if there is a
restricted duct system or motor failure. If limit control does
not function during this test, cause must be determined and
corrected.
a. Run furnace for at least 5 minutes.
b. Gradually block off return air with a piece of cardboard or
sheet metal until the limit trips.
c. Unblock return air to permit normal circulation.
d. Burners will re-light when furnace cools down.
2. Check draft safeguard switch.
The purpose of this control is to cause the safe shutdown of the
furnace during certain blocked vent conditions.
a. Verify vent pipe is cool to the touch.
Fig. 46—Gas Control Valve
A04166
REGULATOR
SEAL CAP
REGULATOR
ADJUSTMENT
SCREW
REGULATOR SPRING
GAS PRESSURE
REGULATOR
ADJUSTMENT
MANIFOLD
PRESSURE TAP
INLET
PRESSURE TAP
ON/OFF SWITCH
1/2˝ NPT INLET
1/2˝ NPT OUTLET
Fig. 47—Orifice Hole
A93059
BURNER
ORIFICE
Table 9—Speed Selection
COLOR SPEED AS SHIPPED
White Common BLW
Black High COOL
Yellow† Med-High SPARE
Blue* Med-Low SPARE
Red* Low HEAT
* 1/5 HP motor models: BLUE to HEAT, RED to SPARE
† Not available on 1/5 HP motors.
NOTE: Continuous blower is the HEAT speed.
Fig. 48—Amp Draw Check With Ammeter
A96316
R Y W G
10 TURNS
THERMOSTAT SUBBASE
TERMINALS WITH
THERMOSTAT REMOVED
(ANITICIPATOR, CLOCK, ETC.,
MUST BE OUT OF CIRCUIT.)
HOOK-AROUND
AMMETER
EXAMPLE:
5.0 AMPS ON AMMETER
10 TURNS AROUND JAWS
=
0.5 AMPS FOR THERMOSTAT
ANTICIPATOR SETTING
FROM UNIT 24-V
CONTROL TERMINALS
34
To Next Page
Loading...
