New V70R owner, got some issues w/ A/C, and a few fluid questions

[aznatama]

Just picked up a V70R a/t that's pretty clean for its age, but have a few issues I'd like to sort out, and couldn't seem to find the answer to after a quick google search.

The AC runs fine, but right after I gave the car a car wash, it would only blow hot air EXCEPT when I turn it onto the coldest setting. After a bit, it returned to normal, but then an hour later, the problem repeated again. At first I thought this could be the interior temp sensor that's faulty, but it starts working again, so I'm not sure what it could be. Any thoughts?

Also, I am planning to change all the fluids to synthetics. Recommendations on what to use?

Thanks