Cold at speed, warm at idle
This is the most diagnostic symptom in car air conditioning. Driving forces air through the condenser at the front of the car; at idle, only the fan does that. If it is cold moving and warm stopped, suspect the cooling fan or a condenser packed with leaves and road debris rather than a refrigerant problem.
Why a top-up is not a repair
If the system is low, refrigerant escaped somewhere — an O-ring, a hose, the condenser, or the compressor shaft seal. Recharging without finding that leak buys a few weeks and vents refrigerant into the atmosphere. We use dye or an electronic detector to find it first.
The R-1234yf cost jump
Vehicles from roughly 2015 onward increasingly use R-1234yf refrigerant, which costs several times more than the older R-134a and requires different equipment. This single factor is the biggest variable in an AC bill, and it is decided by what your car came with.
Warm on one side only
On a car with dual-zone climate control, warm on one side and cold on the other usually points at a blend door actuator rather than refrigerant. It is an electrical part, and often behind the dash — inconvenient to reach, but not a refrigerant issue at all.