Haier Kegerator temps issue

I am new to kegging and kegerators. I bought a Haier Kegerator (Brewmaster) used and i'm having problems getting the temps cold enough. I put a glass of water inside and the temp reads ~43-44. There was supposed to be a trick where you could adjust a tiny screw on the thermostat to make it colder and I did that. No luck. The cold plate has a good chunk of ice/frost built up on it. I'm sure that probably has something to do with it. Any suggestions on what to do to get the temp lower? Will an external temp controller work? How do I defrost the cold plate? I just want to drink COLD beer from my first keg!

If it's not self defrosting, unplug it and put a pot of boiling water in it. The steam should defrost it. This is what I do anyways...not sure if it's the right way...but it works.

I had this same issue with my used Haier kegerator I picked up on craigslist ($50 including two full CO2 tanks!). I ended up throwing a small fan inside the kegerator to circulate the air and it has made a huge difference. Before I did that, I could not get the temp below 40 even on the coldest setting. Now I have it at just below the warmest setting and its around 36-38 degrees. And there is no more ice/frost build-up on the cooling plate in the back.