The single Blue wire at thermostat is the (-) furnace signal lead to the control box mounted up in the ceiling..
The Suburban uses two blue wires. Plus and minus signal to turn energize control module , run fan, etc
In your case you need to locate where the plus side of signal wire for furnace went to before pulling our the furnace.
Your issue .. fan runs but no heat could be several things but a multi meter will narrow down issue.. Looking at it will do nothing
Remove sail switch and ohm out the two contacts while moving paddle on sail switch...must show open one way with paddle and full continuity with paddle arm moved other direction
You are looking for a reading of less than 1 ohm for continuity side...
When furnace fan was running did you listen for tell tale indication of igniter firing at exhaust.. if it was firing then sail switch is not your issue
If it wasn’t firing then either sail switch is bad, loose connections at furnace igniter module or bad igniter module
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2007 GMC Classic club cab 4x4 Duramax LBZ
2014 Alpine 3010 RE. 34 foot fifth wheel
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