Troubleshooting Guide

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EXAMPLE

Start Here Section

ACTION

Step 1 tells us to remove control door first and NOT TO REMOVE THE

BLOWER DOOR because it will erase status codes stored in memory. It then asks the question, "Is RED LED status light on?" If low-heat pressure switch was defective, a low-heat pressure switch did not open, and a status code would be flashing, so the answer is YES. We go to Step 2.

Step 2 asks the question, "Is RED LED status light blinking rapidly without a pause?" If low-heat pressure switch was defective, a low-heat pressure switch did not open, and a status code would be flashing, so the answer is NO. We go to Step 4.

Step 4 asks the question, "Is RED LED status light blinking ON/OFF slowly with a combination of short and long flashes?" If low-heat pressure switch was defective, a low-heat pressure switch did not open, and a status code would be flashing, so the answer is YES. We go to Step 5.

Step 5 tells us to determine the status code. The status code is a 2 digit number with the first digit determined by the number of short flashes and the second digit by the number of long flashes. So we count the short and long flashes and see that status code 23 is flashing and go to Step 6.

Step 6 tells us to go to Status Code 23 section.

If a 2-stage heating thermostat is to be used, move SW-2 to ON position at end of furnace installation. This overrides the built-in control process for selecting high and low fire and allows the

2-stage thermostat to select gas heating modes. W2 from thermostat must be connected to W2 on control terminal block.

This furnace is equipped with a manual reset limit switch in the gas control area. The switch will open and shut off power to the gas valve, if a flame rollout or overheating condition occurs in the gas control area. DO NOT bypass the switch.

Correct inadequate combustion-air supply, component failure, or restricted flue gas passageway before resetting the switch.

Before operating furnace, check each manual reset switch for continuity. If necessary, press and release the button to reset the switch.

SEQUENCE OF OPERATION

Using schematic diagrams in Appendix A, follow the sequence of operation through the different modes. Read and follow diagram very carefully.

NOTE:

Permanent-split-capacitor (PSC) motors and G.E. Integrated Control Motors (ICM) operate differently. PSC motors are basically fixed-multiple-speed motors, that is they operate within small ranges of speed. The ranges, usually 4, can be selected by connecting to different 115-vac motor wires. The speed ranges are small, about 100 RPM wide, and are dependent on the motor’s synchronous speed (1200 for most furnaces). The characteristics of

PSC motors limit selections to fixed speeds between about 700 and

1100 RPM. The ICM motor speeds are infinitely variable from 300 to 1400 RPM and are dynamically controlled to precisely control airflow CFM. The start and stop characteristics of PSC and ICM motors differ in that PSC motors ramp up to speed rapidly and coast to a stop slowly. ICM motors ramp up to speed at a controlled rate to reduce start-up noise perception (4 to 11 sec, depending on target operating CFM). ICM ramp-down time is the same as ramp-up time. ICM ramp-up and ramp-down times are additive to blower on and off delays, respectively. The PSC motor is energized with 115 vac only when operating. The ICM is energized with 115 vac whenever power is available at furnace control, but operates only when 24-vac motor control input(s) are

ON. Other motor differences will be included in the following information.

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INDEX

NOTE:

If a power interruption occurs during a "call for heat"

(W/W1 or W/W1-and-W2) and if thermostat is still calling for gas heating, the control starts a 90-sec blower-only ON period 2 sec after power is restored. The red LED will flash status code 12 during the 90-sec period, after which LED will be on continuously as long as no faults are detected. PSC motors operate at low-gasheat or high-gas-heat CFM, respectively. ICM motors operate at low-gas-heat CFM in both cases. After the 90-sec period, furnace responds to thermostat normally.

Blower door must be installed for power to be conducted through blower door interlock switch ILK to furnace control CPU, transformer TRAN, inducer motor IDM, blower motor BLWM, hot surface ignitor HSI, and gas valve GV.

Step 1—Adaptive Heating Mode—Single-Stage

Thermostat with 2-Stage Heating

NOTE:

With high-heat-only switch SW-1 in OFF position, lowheat-only switch SW-2 selects either low-heat-only operation mode when on (see Step 2 below), or adaptive heating mode when off in response to a call for heat. (See Appendix F.) When high-heat-only switch SW-1 is in ON position, it always initiates high-gas-heat operation when R-W/W1 circuit is closed, regardless of setting of low-heat-only switch SW-2.

These furnaces can operate as a 2-stage furnace with a single-stage thermostat because furnace control CPU includes a programmed adaptive sequence of controlled operation, which selects low-gasheat or high-gas-heat operation. This selection is based upon the stored history of the lengths of previous gas heating on/off periods of the single-stage thermostat.

The furnace starts up in either low- or high-gas heat. If furnace starts up in low-gas heat, the control CPU determines low-gas-heat on time (from 0 to 16 minutes) which is permitted before switching to high-gas heat.

If power is interrupted, stored history is erased. When this happens, the control CPU selects low-gas heat for 16 minutes and then switches to high-gas heat, as long as thermostat continues to call for heat. Subsequent selection is based on stored history of thermostat cycle times.

When wall thermostat "calls for heat," R-W/W1 circuit closes. The furnace control performs a self-check, verifies low-heat and high-heat pressure switches’ contacts LPS and HPS are open, and starts inducer motor IDM in low speed or high speed as appropriate.

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