Pentax DA 16-50 wont focus

Just got the pentax K5 with the refurbished DA 16-50 F2.8 lens. It does not work in AF. The button on the side of the lens can be on AF or MF and only MF works. The shutter wont release unless I manually focus it. ON camera the AF-C or AF-s button doesn't make a difference. Do I have a defective lens?

2. How do I test for sensor stains/ Point at a blue sky at F22 or higher , focus to infinity and and overexpose by 2 stops? Thanks

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