Goodman Furnace: ComfortNet data line check – Goodman *MVC95/*CVC9

ComfortNet data line check - Goodman *MVC95/*CVC9 on a Goodman furnace: How to check the two communication wires (data 1 and data 2) when the furnace, thermostat and outdoor unit are not talking.

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Applies to: GMVC95/AMVC95 upflow and *CVC9 counterflow two-stage furnaces

Common causes of comfortnet data line check - goodman *mvc95/*cvc9

• Dip switches set wrong
• Data wires reversed, broken or shorted
• Wire run too long

How to fix comfortnet data line check - goodman *mvc95/*cvc9: step by step

1. With power on, measure data 1 to C: about 2.6 V DC. Data 2 to C: about 2.3 V DC. Data 1 to data 2: about 0.2-0.6 V DC.
2. With all bias and termination dip switches ON you should read over 2.5 V (1-C), under 2.5 V (2-C) and over 0.2 V (1-2).
3. On the furnace control, BIAS switches 1 and 2 and TERM switch 3 should all be ON. The outdoor unit TERM switches should also be ON.
4. Reading 5 V / 0 V / 5 V or 0 / 0 / 0 points to a switch set wrong or a wiring fault. Fix the switch or wiring and retest.
5. Use 18 AWG thermostat wire, max 100 ft from furnace to outdoor unit or to the thermostat.
6. Press the learn button for about 2 seconds to reset the network after any change.

If the unit shows an error code, look it up: Goodman Furnace codes

Models

GCVC90704CXGCVC90905DXGCVC91155DXGCVC950714CXGCVC950915DXGMVC950453BXGMVC950704CXGMVC950905CXGMVC950905DXGMVC951155DX