035-15241-003 Rev. A (201)
18
Unitary Products Group
BLOWER TIMINGS
The electronic furnace control supplied on this furnace con-
trols the blower delay timings.
The heating on delay, from when the gas valve opens to
when the circulating blower comes on, is fixed at 30 seconds
and is not adjustable.
The heating off delay, from when the gas valve closes, to
when the circulating blower shuts off, is factory set at 120
seconds. This timing may be adjusted to 60, 90, 120 or 150
seconds on the electronic furnace control. The furnace con-
trol has four pins and a small jumper plug, which is used to
adjust the blower off delay. See Figure 13.
DIAGNOSTICS
The electronic furnace control supplied on this furnace is
equipped with a diagnostic light, which flashes when there is
a service problem with the furnace. The number of times the
light flashes indicates the location of the problem, as listed
below:
Steady off -
Normal operation
One flash -
False flame sense - Check for stuck open gas
valve.
Two flashes -
Pressure switch stuck closed. Check for
shorted wires, bad pressure switch.
Three flashes -
Pressure switch failed to close - Check vent
blower, pressure switch, vent blockage, disconnected pres-
sure hose.
Four flashes -
Limit switch open - Check for open limit
switch, loose connections in limit circuit.
Five flashes -
Rollout switch open - Check for open rollout
switches, loose connections in rollout switch circuit.
Six flashes -
One hour pressure switch lockout - Pressure
switch has cycled four times in a single call for heat - Check
for vent blockage, loose connections in pressure switch cir-
cuit.
Seven flashes -
One-hour ignition lockout - Burner failed to
light in three tries - Check gas flow, gas pressure, gas valve
operation, flame sensor.
Eight flashes -
One-hour ignition lockout - Five recycles in a
single call for heat. Check gas flow, gas pressure, and gas
valve operation, flame sensor.
Nine flashes -
Reversed line voltage polarity - Check incom-
ing power wiring for proper polarity.
Eleven flashes -
Jumper wire on control board is discon-
nected, or furnace is improperly grounded.
Steady on -
Gas valve energized with no call for heat from
thermostat, or, control failure.
FIGURE 13: BLOWER TIMING CHANGE
90
120
150
60
PUT JUMPER PLUG ACROSS PINS
FOR DESIRED BLOWER DELAY
TIME (90 SECONDS SHOWN)