My '96 Civic EX has never had the air conditioning gas replacement, but I've noticed it's not as cold as it used to be.

What is the best gas out there for replacement for my car? Is it easy enough DIY job?

 

if by gas, you mean the refrigerant, there is only one type you can put in it, it's R134a. If you put anything else in it, the a/c system will fail. in order to do this correctly, you would need to get a hold of some manifold gauges that tell you what the pressures are in the high and low sides of the system.

go to my signature and download the 96-98 civic factory service manual. it will tell you all that you want to know.

 

Check the water valve first. It's a very common reason for the air to not be fully cold. The lever on the valve needs to move all the way to closed when you put the dash control on full cold.

It's normal to have lost a little refrigerant after so many years. Use only plain R-134a. Do not use "leak stop." "high mileage," etc. Those additives are more harm than good. You should need less than a full can to "top up". Watch the high side gauge and don't overcharge. Don't try to charge with one of those cheap hoses that only has one gauge.