So, when you are in the defrost mode the compressor will run, I would unplug the A/C clutch to stop the operation. You are correct on the ground wire which can cause problems. To confirm the bad ground, use a test light and probe the black wire when the blower is not working and if it lights up the ground is bad.
Here is a guide to help:
https://www.2carpros.com/articles/how-to-check-a-car-fuse
This guide may help as well:
https://www.2carpros.com/articles/blower-fan-motor-works-on-high-speed-only
I have included the blower motor wiring diagrams so you can see how the system works. Check out the images (below). Please let us know what happens.
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Monday, March 27th, 2023 AT 11:45 AM