No fan at all on Heater or Vent

[82DMC12]

Hey guys,

Working on a weird problem. My HVAC works fine in all positions however I have no fan at all when the mode switch is on Heater or Vent. Everything works normally. I pulled the mode switch out and disassembled it completely. Cleaned all the metal contacts and re-lubed the rubber maze. I confirmed the three wires that connect to the switch are in place and in the correct positions. Since it appears the mode switch feeds the fan switch directly, I guess there must be a problem with the mode switch. I'll put it out again and check it with a meter but has anyone seen this and is there another part of the puzzle I'm overlooking?

[82DMC12]

So I pulled the switch out again and confirmed I have continuity between the two outer pins (LG/W) and (LG) in all mode positions except for OFF. That seems to confirm the mode switch itself is working.

[Ron]

Since the fan works on AC but not Heat, it has to be the mode switch.
I'd guess that, although you show continuity between the two outer pins (LG/W) and (LG), the contacts inside the mode switch will not handle the load (amperage) required by the fan motor.
You can confirm by jumping Battery 12V to the (LG) wire, which should make the Fan work at any speed position, regardless of Mode Switch position.

[82DMC12]

Figured it out! The bottom terminal in this picture was allowing the spinning metal selector to make contact in a neutral position, with no pressure on the terminal. Once it was installed, the wire was tugging on the metal terminal a bit causing it to disconnect internally. The solution for now was to simply shim the trace up slightly with a piece of cut-up business card. Now it has enough upward pressure to touch the spinning selector no matter how the tab is being pulled. This repair also gave me a chance to replace the white plastic T-tab which had broken last time I was in here but I had a spare in a drawer.

PXL_20211120_185854242.jpg

[82DMC12]

The mode switch is working perfectly fine now. Shimming the copper trace helped, and for extra measure, I tightened a zip tie around all three wire terminals so that no single tab can be tugged, causing an internal break, in the future.

PXL_20211120_191158320.jpg