The standard price is 99.95 for the service and .99c per ounce of freon that the vehicle is low on for R134A systems. If you have a newer system with R1234yf then the cost of refrigerant is 5.50 per ounce.
Yes. The air coming out of your vents may be cold enough to keep you happy, but it doesn't mean that your system is charged to specification. It may be as much as 20 percent low and still make reasonably cold air. If you wait until it stops cooling, you increase the chance of additional damage.
A normal A/C Service takes 1-2 hours depending on the type of system.
No. When we service a car air conditioner, we evacuate all refrigerant, and perform a vacuum leak test. We then reuse that refrigerant plus the amount needed for a full charge and add dye to the system so we can detect any leaks going forward. You pay only for the additional amount of refrigerant needed.
This can cause damage to your system since you have no idea of knowing how much refrigerant was in your system when you started. Overcharging can cause issues with the system due to higher pressures that can damage your compressor and condenser because of this, leading to an expensive repair down the road.
R134a and R1234yf are similar, however, R1234yf was created as a more environmentally friendly replacement to R134a. The biggest difference between the two, is that R1234yf is mildly flammable and does require special handling.
The short answer is no, as R12 is no longer available. What we can do is retro-fit your older system to use the newer R134a refrigerant so that you can service it as needed going forward.
You could possibly have a slow leak that wasn't showing up on the initial service. Or possibly a part failed that was working normally prior. Let the shop know you just had it serviced and it isn't working again. Most shops will take care of you.
You may have a low charge or bad actuator or door issue. Make an appointment with a certified A/C facility to have it looked at.
It can last for years. Of course a failure of a seal, hose or hard part can cut that down significantly.
A short answer is inside the condenser has flowing superheated refrigerant brought to scalding temperature due to the heat of compression. The condenser will need moving air to transfer heat away from it and into the air outside. During idle, the condenser depends on the external A/C fan to pass air across the fins to provide the cooling. It is normal for the temperature to increase some but if it increases significantly there may be an issue.