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Ok, here we are at the indoor furnace, you may be in the attic or you may be in the garage.

In the very beginning you verified that there was air movement from the vents.

That told us there was 115 volts to the control board and that the line of power , continued on through the transformer where it got converted to 24 volts. One side went to the board and the other side of 24 went down through red to the thermostat and that it came back from the thermostat and closed the fan relay on the circuit board, bringing on the blower motor.

But you’re here now so to be sure, lets double check that large assumption.

Pic of an in garage furnace and coil

Remove the panels and access the blower housing and the circuit board.

 

Now, jumper the door switch and wait 5 minutes for any time delays we initiated to elapse.

 

Now when your sure the thermostats time delay is over, test for 24 volts at terminals C and G on board.

If you do not have 24 volts at Common and Green which is the fan terminal, move to page 28 now.

No 24 V at C and G Lets go to page 28 now

Yes I do have 24 volts at C and G that’s good then continue through page

Now check for 24 volts at C and Y terminals of control board. (Note: If the yellow wires are not attached to the circuit board, then place one lead in the yellow wire nut and the other at common or C of control board.)

If you DO NOT have 24 volts at C and Y then we have a broken thermostat so move to page 32 now.

 

Let’s go change a thermostat in page 32

Yes, there is 24 volts at C and Y then continue

Since we already know the 24 volts does not make it all the way outside, you have a broken wire in between the furnace and the ac condenser.

First, try using a different color wire that is not currently used and make sure to switch the yellow wire for the new color at the furnace and the condenser.

But, if there are no extra wires , you’ll have to run a whole new minimum 5 strand thermostat wire to connect the condenser and the furnace. After this is done re-start the matrix on page 1.

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