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To test the cooling system directly at the indoor unit without a thermostat or thermostat wiring, you need to jump the low-voltage terminal strip on the furnace integrated control board. Your International Comfort Products (ICP) N9MSE1202420A2 is a 95% AFUE single-stage gas furnace; testing the AC requires a simultaneous call for both the indoor blower fan and the outdoor condensing unit. [1, 2, 3]

1. Gain Control Board Access

• Turn off the main electrical power to the furnace using the service switch or circuit breaker.
• Remove the furnace blower access door to expose the integrated control board.
• Locate the low-voltage terminal block labeled R, C, G, Y, W. [4, 5, 6, 7]

2. Connect Your Jumper Wires

• Use an insulated alligator clip jumper wire to bridge the R (24VAC hot) terminal to the Y (cooling call) terminal.
• Use a second jumper wire to bridge the R terminal to the G (indoor fan) terminal.
• Note: You must jumper both Y and G simultaneously on this model to force both the indoor blower motor and the outdoor compressor contactor to pull in together. [3, 7, 8, 9, 10]

3. Verify the Condenser Splice

• Ensure that the two field-installed low-voltage wires running from the outdoor condenser unit are securely connected to the Y and C (common) terminals on this board. [7, 11]
• If there are no field wires landed on the control board at all, you will need to wire your jumper directly from R to the condenser’s contactor coil wire, while the other side of the contactor coil lands on C. [7, 12]

4. Energize and Observe

• Securely tape down or manually depress the furnace door safety switch to allow the 120V line voltage back into the system.
• Restore the main electrical power.
• The indoor blower should kick on immediately, and the outdoor compressor/condenser fan should ramp up. [5, 8, 13, 14, 15]

5. Shut Down Safely

• When testing is complete, disconnect the main power source first before removing your jumper wires.
• Removing jumpers under power can spark and easily pop the low-voltage blade fuse (typically a 3A or 5A automotive fuse) on the ICP control board. [8, 9]

✅ Verification

The cooling circuit will successfully activate when R is jumpered directly to both Y and G while the outdoor contactor loop is completed across Y and C. [3, 7] If the system fails to start with these jumpers in place, let me know:

• Is the control board displaying any flashing LED diagnostic fault codes?
• Are you reading 24VAC across R and C using your multimeter?
• Is the outdoor contactor physically pulling in, or is it silent? [12, 14, 16]

I can walk you through checking the transformer or diagnosing a low-voltage short based on what you find!

[1] https://www.shareddocs.com [2] https://www.partstown.com [3] https://www.youtube.com [4] https://www.justanswer.com [5] https://www.youtube.com [6] https://www.shareddocs.com [7] https://www.youtube.com [8] https://www.justanswer.com [9] https://www.appliancepartspros.com [10] https://www.youtube.com [11] https://www.justanswer.com [12] https://www.youtube.com [13] https://www.shareddocs.com [14] https://www.youtube.com [15] https://www.nordichomeinspection.com [16] https://www.manualslib.com