Can someone tell me what’s going on!

I have finally come across an issue I never thought I would see in my life–a draft I cannot fix. I’m accustomed to living in quirky old homes with their own odd little issues. Though I’m a young woman, I already know how to fix a great deal of things. I can mend a toilet that won’t stop flushing, seal up windows in a pinch, heat up a bedroom during a power outage through the use of candles, and I can even light a gas boiler that doesn’t have a pilot light switch. I’ve mended drafty windows and doors with everything from actual door sealing socks, blankets over curtain rods, and at one point in time, towels. But I have faced an enemy I cannot suss out–a drafty slider door. What’s worse, is the thing doesn’t even appear to be old–it still had the sticker on it when we moved in! Unlike a normal door, I can’t put a door sock on it. As far as I can tell, the door is crooked in the casing, so it’s not closing properly. My boyfriend suspects it wasn’t installed properly. This dang door is making us lose precious heat from our oil boiler, and there’s nothing I can do about it but hang energy saving curtains over it. As its a main door for the home, I can’t seal it up and ask people not to use it either. I’ve called my landlord about it, but he says its brand new and doesn’t need to be repaired. I’m just hoping the Energy Star curtains at least help keep some of the cold air out, and the hot air in. I’m all out of energy saving tips to try on this one.

A/C system