My fridge and freezer are not cooling properly. There is cool air blowing but it is not frigid cold. This is an older model fridge that has coils rather than compressor fan. I have cleaned coils already. This problem started approximately 2-3 weeks ago but has slowly gotten worse. Via research I have done the basic troubleshooting techniques like check evaporater fan and coils which both seemed to be functioning properly. I noticed when I unplugged system to reset it, the compressor would not come on like it should. I'd get a "click, buzz, click" which led me to believe compressor problem. Last night I installed a 3&1 hard start kit and the compressor immediately came on when I plugged in. I believe it's been running non stop ever since. My hope is that it's just doing this in attempt to bring temperature back to normal and I gather that could take up to 24 hrs. My question is if it does not show signs of achieving proper temps, what could be the problem? I was thinking thermostat/cold control would be the culprit and need replacing but I had someone with HVAC experience say it's probably a freon problem since compressor came on. I thought if compressor continually ran it'd be because it's trying to achieve a certain temp but can't due to faulty thermostat reading. At the same time if my thinking is incorrect I don't want to waste $100 on a thermostat that won't fix my problem...please help and thanks in advance.

There was a light frost when I checked earlier this week on coils to top left where I assume freon is pumped through. Temperature in freezer averages around 40-45 degrees.

Ok. Thank you for your time and advice. How would I go about finding out which kind of freon I'd need?