Getting a letter of recommendation when the referee gave no indication about the strength of the letter Usually when I ask for a letters of recommendation, the professor give me an indication about how strong it is going to be. I asked a professor whom I am taking a course with, and while he doesn't know me very well, I did well in his course project which made me think that he might write a good letter. So I went and asked him (Before project submission) and he said that to put his name as a referee and gave me no indication about how strong it is going to be. He also said that he is looking forward to read my project report. (I told him it is a chance to get to know my work).  

The next day I submitted project report and a few hours later I received an email from him telling me that he didn't receive letter submission link yet. I went and asked him what did he thought about the report and he said that he didn't read it yet. I hesitated because I already have 3 letters and his would be the fourth one which is really an extra. 

A few days later, I ran into him and again he mentioned he didn't receive submission link and again I asked if he read the report and got the same response. This situation is a little confusing for me because I would rather not having his recommendation if it is not a strong one. On the other hand, he asked me three times to put his name as a referee which made me think that he is going to make a good letter. 

Since I already have all the letters I need, should I take the risk of having his letter ? (I am applying to a long shot school anyway and he is well connected in that school, so his letter weights a lot, whether it is positive or negative)
Two things.

First, he is demonstrating strong willingness to write a letter for you. Although you can't know for sure without asking directly, this is a good indication that his letter will be strong. 

Second, ASK! In this situation, don't be afraid to ask him bluntly, as ff524 recommended. 

Finally, in future, you can avoid some of this uncertainty by phrasing your request this way: "Are you willing to write a strong letter of recommendation for X application?" In this way you are asking not just for a letter, but for a strong letter, and their response will be more indicative of the strength of their letter. 

And for this one, all indications point toward it being a risk worth taking. Best of luck on your application!