It doesn’t take a licensed mechanic to realize that when warm air starts coming out of your A/C vent, there is something seriously wrong with your vehicle’s climate control system.

When your air conditioner feels “weak” or blows only warm air, it’s likely low on refrigerant. That could mean it’s time for an air-conditioning recharge, but there’s more to it than simply filling it back up. Because the refrigerant is contained inside what should be a closed system, the most likely cause for low levels is a leak. All dealerships have qualified technicians that will inspect the system for obvious leaks in hoses, pipes or the air-conditioning compressor itself, and who will make repairs as necessary.

After inspecting the system, the technician extracts the remaining refrigerant into recycling equipment that removes any impurities, recharges the system by injecting the “clean” refrigerant back into the system, and tops it off with fresh refrigerant as needed. Regulations forbid releasing refrigerant into the atmosphere, and specialized equipment is required to extract it. The technician then tests the system and runs an electronic leak test.

Can you save money by topping off the system with refrigerant? Possibly. Could you do it yourself? Sure, kits are available from automotive stores. But there are major issues with that approach that most people aren’t aware of.

There’s no way of knowing how much refrigerant is left in the system, so even a qualified technician would have to guess as to how much refrigerant to add. Systems vary, but each one holds a specific amount of refrigerant. The only way to know that an air conditioner is full is to evacuate the system and fill it with the specified amount.

Topping off the refrigerant doesn’t fix leaks or whatever other issue caused the system to run low, so it’s only a temporary fix at best. The air conditioner might work for a while, but most systems are designed to shut down once the refrigerant falls to a certain level. Eventually, it will just blow warm air.

Small leaks such as pinholes in hoses can be hard to find, so you might find yourself back at the shop even after a complete evacuation and recharge. The air conditioner might stop working, and when you return to the shop, the technician might have to inject dye into the system and trace it with a black light for leaks. Sometimes the leaks occur in hidden locations such as the evaporator, which is well behind the dashboard.

As long as your air conditioner is blowing cold air, there’s no need to recharge or “top off” the system with refrigerant, but if the system feels weak or blows warm air, there’s no shortcut that will get you back on track. In fact, those shortcuts may cost you even more money by prolonging a proper repair and putting a strain on the entire system, so make an appointment immediately and have the proper repairs done before things get worse.