I have a 95 civic dx with a 98 civic dx engine. I bought this car from someone who just swapped the engines and I dont know if they replaced the freon in the a/c system. It only blows warm air. I checked the low pressure and it was 0. So I bought a recharging kit and emptied about 17 oz in it and the pressure did not go up. I checked and I didnt see anything leaking. The fan comes on , but now it doesnt when i press the a/c button.

 

If the pressure didnt go up, then there has to be a leak somewhere

 

You must measure refrigerant pressure on both the high and low sides using a manifold gauge. Knowing the pressure on both sides will allow you to better troubleshoot the problem.
By the way, the refrigerant capacity of a 95 A/C system is 23 oz.

Correction: As mentioned by mk below, the 95 A/C system uses R134a.

 

The 95 takes 134a. +1 on there is a severe leak or a part missing. Check everything thoroughly. Do not assume that the system was OK before the engine swap.

You need to pump the air out of the lines with a vacuum pump before recharging. Charging on top of the air gives you a mixture of refrigerant and air which will impair cooling performance considerably.