Central air conditioners should never need more refrigerants. You should not have to charge the system at any time. Needing more refrigerant is a sign that something is wrong with your air conditioner.
There are a couple of reasons that an air conditioner may need to be charged. The first is that it is leaking refrigerant. The second is that it is older and becoming less efficient. While it may be tempting to just charge your air conditioner and move on with your life, don’t do that. Residential air conditioners should not need to be charged. If yours does, that means there is a problem. Instead, contact your local HVAC experts, like Russell’s in Greater Yucaipa, CA, immediately.