You need to look at the closing mechanism and the exterior clearances.
When the window is closed, do you see equal spaces around the perimeter. If it rubs, it won't close properly and the winding mechanism will wear out quickly.
Ron

By exterior clearances do you mean space around the window or anything interfering with the closing? That looks OK. (This is a summer house so I'm not there at this moment, but that's my recollection.) The way it cranks open but not closed is what I find odd.

Watch all moving parts throughout the entire range of motion as you are opening and closing the window. Check around the window and and in the operating arm track at the bottom for any rubbing or binding that impairs free operation. Does the window close flush against the frame or does one corner contact well before the other? With the operator cover removed, check for excessive play or wear between the gear teeth.

Thanks, I'll do that when we get to the house. Since it can be cranked open in one direction but not the other, I suspect a gear issue. I hope that can be rectified by just replacing these parts, but I'll just have to see. Replacing the entire assembly seems like a big job.

I had the same problem. You need to replace the arm operator. I ordered a couple of them online from windowparts.com . Not difficult to do. You just need to identify the type of arm before buying. They have had several different types over the years. Mine had the split arm operator.

Thanks very much. I was afraid of that, but I was hoping that perhaps it might have been something in that small unit that you see in the picture. By "arm operator" do you refer to the metal thing that actually pushes the window open and closed? I've seen instructions for replacing that and it seems like a big job.

I'm not sure I could too precisely describe the window model etc. as I just bought this house and the window may be 30+ years old.

My husband and I recently replaced the operator on an Andersen casement window that looks like yours. Our house was built in 1984, and one of the bedroom windows had the same problem that you describe: it would open but closing it involved removing the screen and pulling the window shut by hand.

The operator cost about $50 including shipping from Windowparts.com. We waited until the weather was not too hot, not too cold, and not windy. We followed the instructions provided in the link below. The only difficult part is removing the trim without breaking it. I was able to get a putty knife underneath the trim and located the two finishing nails that were holding it in place, and my husband cut them by sliding a hacksaw blade underneath the trim. We took our time carefully prying the trim up, and the whole process took maybe 20 minutes. Our trim is painted, so scraping, sanding, and painting took another 30 minutes are so. It would have taken longer if I hadn't painted the trim a few months ago, but because I had, I had to paint only the immediate area where we worked.

Good luck!

Here is a link that might be useful: How to Replace an Andersen Casement Window Operator