Furnace Fails to Operate, Twinning of Two Furnaces

A second trial for ignition (step 6) begins if no ﬂame is sensed. On the ﬁfth try for ignition, the furnace control is locked out and the red LED will blink 4 times repetitively. The thermostat must be opened for at least ten seconds to reset the furnace control after a lock out. Otherwise, the furnace will attempt another ignition sequence in 1 hour.

8.The furnace control energizes the circulating air blower on the heating speed 30 seconds after the gas valve circuit is energized .

9.When the thermostat has been satisﬁed, gas valve is de-energized.

10.The inducer is de-energized after a 30 second postpurge.

11.The furnace control keeps the circulating air blower energized for 120 seconds (factory set) or 60, 90, or 180 seconds (ﬁeld adjust- able). (See Figure 27.)

12.Abnormal conditions: If a limit opens during operation, the inducer and circulating air blower continue to operate. The gas valve is de-energized immediately. The blowers continue to operate until the limit closes. When the limit closes the inducer blower is de-energized immediately. The circulating air blower continues to operate for the speci- ﬁed delay (factory set at 120 seconds).

Cooling Mode:

1.On a call for cooling the thermostat closes, applying 24 VAC to the G and Y terminals on the furnace control. This closes the compressor contactor.

2.The furnace control energizes the circulating blower (115 VAC) on the cooling speed.

3.When the thermostat is satisﬁed, the G and Y terminals on the control board are de-ener- gized opening the compressor contactor.

4.The circulating air blower is de-energized after a 90 second delay.

Fan Mode:

1.On a call for fan operation, the thermostat applies 24 VAC to the G terminal on the furnace control board.

2.The circulating air blower is energized im- mediately on the heating speed.

3.If the furnace is operated in the continuous ON position at the thermostat and is then switched to AUTO, the circulating blower will operate for a speciﬁed delay (factory set at 120 seconds).

Furnace Fails to Operate

If the furnace does not operate check the fol- lowing:

1.Is the thermostat operating properly?

2.Are the blower compartment door(s) in place?

3.Is the furnace disconnect closed?

4.Has the circuit breaker tripped or the control board fuse burned open?

5.Is the gas turned on?

6.Are any manual reset switches open?

7.Is the ﬁlter dirty or plugged?

8.Is the ﬂame sensor coated? (Remove and clean with emery cloth.)

If the furnace locks out after 5 attempts for ignition, it will try again every hour if a call for heat remains. If the inducer and circulating air blowers are operating, and items 1 through 8 have been checked, press the red reset button on the vent safety switch. (See Figure 30.) If the furnace operates after depressing the reset button, contact a qualiﬁed serviceman to identify and repair the problem.

If the furnace continues to not operate, depress the red reset buttons on the ﬂame rollout switches. (See Figure 30.) If the furnace operates after depressing the reset buttons, contact a qualiﬁed servicemen to identify and repair the problem.

Thermostat

W G Y R

A/C

Unit

G W

Twin Terminal

CY Twin

GW Terminal

Twinning of Two Furnaces

The control board on these furnaces is capable of being twinned to another furnace of the same series, provided the circuit boards are both UTEC type. If using UTEC control boards, leave the fuses installed on each board. The thermostat wires and the 1/4 inch quick-connect terminals marked “TWIN” on the furnace controls must be connected together for twinning. (See

Figure 31. Twinning

Figure 31.)