ac causing knock sensor code?

It finally got hot enough and figured it was time to fix the ac in the impreza. Leather seats suck in summertime.Pulled the cap and found out it had a little pressure in it. So picked up a quick charge kit sure enough the ac was blowing cold I was happy but then noticed it had a check engine light. Pulled the code it was the knock sensor. Have a new one to put in,just no time to do it right now, so cleared the code. Started it up no check engine light. Cool. Turn on the ac check engine light comes on. Knock sensor. Anybody else have this problem?