Heater and Windshield Wiper conflict

[f5fstop]

Only thing they have in common, other than battery B+, is the ground point; located under the right (passenger) side kick panel, toward the bottom. I AM NOT implying this is the problem, but I can tell you from many years of experience, ground points sometimes cause circuits to act strangely.
If it were me, I would remove the kick panel, remove the bolt for the ground point, make sure it is clean underneath (no corrosion or paint). If there is corrosion or paint, remove it at the location the washer hits the metal. Re-install, and tighten. When re-installing, make sure all the eyelets are clean where they contact the next eyelet.
It might be a waste of time, but it is only about ten minutes at the most, if you have to clean the location.

I should also ask, did the technician check the battery and the battery connections? Make sure they are very tight. A slightly loose battery connection; positive or negative, can affect some circuits with some strange afflictions, and the vehicle will still start ok.