if i insert more than 3 ad units using iframe is it ok with adsense TOS? and when i insert more than 3 ad unit per one page without using iframe, only 3 ads are visible. others will be automatically disable. why is that?
I have only added one ad in my two blogs, i dont why would you need three ad units on your site or blog, two or one is enough depending what your site or blog is, but your right dont over do it with the ads. Otherwise the users wont bother with your site or blog ads aren't that important. Content is the most important, the more Content the better traffic you will have, if you place more then one ads on your web site or blog the users wont bother your blog or site. Make sure you follow the adsense TOS, dont over do with the ads.
when i insert one or two ads i dont get clicks. but when i insert 3 ads or more than that clicks will be high.
from google adsense polices AdSense for content: Up to three ad units and three link units may be placed on each page. Have you read the google AdSense placement polices?
It has clearly declared by Google that only 3 ad units per page. That the part of their TOS. But i have seen many people ad more than 3 units per page by iframe. Someday they will get caught.
No , only 3 display/block ads , although you can add up to 2 text-link-ads (This would be a total of 5). If you have anymore on the page , it just won't display. If you use things like Iframes to try and cheat the system , you will be banned. You're also allowed to ad other ad networks to the same page to get more than 5 total links , although I wouldn't do it at all.
Currently, AdSense publishers may place up to three AdSense for content units on one webpage. You may also place a maximum of three link units and two search boxes on each webpage.
You don't want to over do the number of Ads on your page. If your goal is to create a lot of legal clicks on your Adsense Ads, place the ads in the best locations on your webpage. Google has good information on the best locations to place the Ads. http://www.google.com/support/adsense/bin/answer.py?answer=17954
I recommend you to put maximum of 2 Adsense ad on your blog. use the official Adsense heatmap and place your ads wisely and optimize them so they'll fit in your template. Respect Adsense TOS or all of your earnings will be lost when they discover that you're cheating the system.
You can only add 3 units on one page... if you add more than 3 units they will not show up ... I have tried that my self