AC intermittently stops working

Hi guys, I recently moved into a small house in Florida. My GC (with the help of an AC tech) had installed an AC about 2-3 months ago. It consists of an outdoor condenser (which was new) and an indoor air handler (which was 2nd hand). Initially the AC worked great, however for the past 2 weeks I have been having problems. Basically the AC will become less and less effective over time. The vents will have significantly lower air output along with passage of only minimally cool air. I can hear the blower making its normal noises during this, despite minimal air output. The first time this happened, I turned the machine off, then restarted it several hours later. It then worked fine for a few days. I would have it on for about 14 hrs a day. The problem started again about a week later. At that time I looked at the air handler, which appeared to be slowly dripping liquid. I did some Googling, which made me think the problem could be frozen coils. As far as why the coils could be frozen, possible causes (according to random websites) included: 1. Poor air flow - Could be due to dirty filter, dirty coils on condenser or air handler, problems with tubing, or due to blocking an excessive amount of vents. With regards to the last point, I have 6 vents in the house and I had blocked all but 2-3 a few weeks before the problem started. 2. Low freon/freon leak At that point I kept the AC off, left the AC's fan on, changed the filter, and let the water drip out overnight. The following morning when I tried the AC, it worked fairly well, though not at 100%.