Circuit Board Diagnostics

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Stuart Wilkins
5 years ago
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1 Circuit Board Diagnostics NOTE: Discharge your body s static electricity before touching unit. An electrostatic discharge can adversely affect electrical components.

If NO 24 volts read, check transformer, thermostat, and wiring.

2 Troubleshoot Integrated Control Module If 120 Volts is Present on the Board Set thermostat to call for heat, and test for 24 volts at W1 and C. If NO 24 volts read, check transformer, thermostat, and wiring. If transformer power is producing 24 volts, but terminal board only receiving 13 volts between C and R, check 3A fuse. (on board) 24 volts to board Neutral wire

Troubleshoot Integrated Control Module- GMVC96 If 120

3 Troubleshoot Integrated Control Module- GMVC96 If 120 volts is Present on the Board 3A fuse Set thermostat to call for heat, and test for 24 volts at W1 and C. If no 24 volts read, check transformer, thermostat, and wiring. If transformer power is producing 24 volts, but terminal board only receiving 13 volts between C and R, check 3A fuse. (on board)

4 Troubleshooting Furnace Circuit Boards 1. Is there a blink code or the code from Digital Display? 2. Does the furnace have a good earth ground? 3. Is there 120 volts (+ or 10%) to the board? 4. Do you have 24 volts to the board? 5. On Communicating Furnaces is the communications light flashing?

5 Troubleshooting Furnace Circuit Boards (continued) 6. Turn the T-stat on and give it a call for Fan on. Is there 24 between G Terminal and common? 7. Check the Molex plug. Does it show signs of corrosion? 8. Are all the stake on tight, and no signs off corrosion? 9. Take the T-stat wire off of the board. Now use a jumper wire to make your call. Example: R to G terminals calling for fan.

6 GMSS Diagnostic Codes

Troubleshoot Integrated Control Module Check for Proper Furnace Ground (GMEC96 and GMVC96 ICM s) The ground wire must run from the furnace all the way back to the electrical panel.

7 Troubleshoot Integrated Control Module Check for Proper Furnace Ground (GMEC96 and GMVC96 ICM s) The ground wire must run from the furnace all the way back to the electrical panel. Proper grounding can be confirmed by disconnecting the electrical power and measuring resistance between the neutral (white) and the burner closest to the flame sensor. Resistance should be less than two (2 ) ohms.

8 Ignition Control Grounding Field Measurements Measure the AC voltage between Line Neutral (spade terminal) and C (Thermostat Terminal Block) on the control This voltage should be less than 2 VAC

9 Ignition Control Grounding Cycle the control so that the inducer and circulator blowers are operated The voltage should not vary An indication of a poor or partial ground is a varying voltage between Line Neutral and C

10 Ignition Control Grounding Field Measurements Measure the AC voltage between Line Neutral (spade terminal) and C (Thermostat Terminal Block) on the control This voltage should be less than 2 VAC

11 Ignition Control Grounding Cycle the control so that the inducer and circulator blowers are operated The voltage should not vary An indication of a poor or partial ground is a varying voltage between Line Neutral and C

Troubleshoot Integrated Control Module - GMEC96 This GMEC96 ignition control module is capable of diagnosing many furnace failures to help in troubleshooting.

12 Troubleshoot Integrated Control Module - GMEC96 This GMEC96 ignition control module is capable of diagnosing many furnace failures to help in troubleshooting. The trial for ignition period is four (4) seconds. Check for 120 volts entering the board at the L1 and neutral pins on the ICM. If no 120 volts read at board, ensure that the door switch is closed. If door switch is closed, but no voltage present, check power source.

13 Test for 120 volts AC

14 IFC Main Harness Connector 15 Pin Connector Pin 1, Limit Switch Input Pin 2, 1 st. Stage PS Input Pin 3, No Connect Pin 4, Hot Side Transformer Pin 5, Earth Ground Pin 6, No Connect Pin 7, Pressure Switch Output Pin 8, Main Valve Common Pin 9, No Connect Pin 10, Hot out to LS Pin 11, 24 Common Pin 12, 2 nd. Stage PS Input Pin 13, Low Gas Valve Main Pin 14, High Gas Valve Main Pin 15, No Connect

15 Troubleshoot Integrated Control Module After Ignitor Warm-Up Time Check for 24 volts to the gas valve. Voltage will be present for four (4) seconds, only if proof of flame has been established. If no 24 volts to gas valve via board, remove 12-pin plug from ICM, and test power directly on board plug, pin #1. If board is not supplying 24 volts, replace board.

Troubleshoot Integrated Control Module- GMVC96 This GMVC96 ignition control module is capable of diagnosing many furnace failures to help in troubleshooting.

16 Troubleshoot Integrated Control Module- GMVC96 This GMVC96 ignition control module is capable of diagnosing many furnace failures to help in troubleshooting. When the control is powered up normally, the light will be on continuously. The display will indicate On when powered in stand-by mode. This can be used to test for 120 volts and 24 volts, as it won t light up unless both are present.

17 Troubleshoot Integrated Control Module- GMVC96 If the On light doesn t come on, check board for 120 volts entering the board at the line and neutral pins on the ICM. If no 120 volts read at board, ensure that the door switch is closed. If door switch is closed, but no voltage present, check power source.

18 Check for Polarization

19 Checking for Phasing

Troubleshoot Safety Circuits

Troubleshoot Safety Circuits Troubleshoot Safety Circuits GMEC96 and GMVC96 Furnaces Safety circuits serve to control any potential safety hazards, and are in place to ensure proper furnace operation.