In Reply to: Air-Con question posted by Air Con question on February 07, 2000 at 09:44:04:
You are getting a hose job, and it is not from the recharging station. R134a which is in your Z3 is not consumed in the air conditioning process. First of all, an air conditioner is nothing more than a refrigerator -- do you have that recharged yearly? The A/C works by plauning around withe the energy it takes to transform a liquid into a gas (the latent heat of vaporization). The radiator-like device in your heater system is called an evaporator. The refrigerant goes through an wexpansion valve just befor eit enters this. The pressure drop across this valve causes the refrigerant to change state from a liquid into a gas. This takes energy, which is sucked out of the hot air in the interior compartment. This gas then travels back to the compressor in your engine compartment which compresses the gas and heats it (by virtue of the compression). The hot gas then goes into the condenser (in front of your radiator) where the hot gas give off heat, cools and condenses back into a liquid refrigerant. From the condenser , it goes back to the expansion valve, and the process starts all over again.
I believe from this description, it should be clear that the A/C is a closed system, and the refrigerant is not consumed. The only way you would need a recharge is if you have a leak in the system. From the standpoint of fixing the cause and not the effect, if your car does need frequent recharging, it is indicative of a leak and it should be found and corrected.
As for "the manufacturer only puts about 30% of the Freon chage in" -- stand in front of the condenser for a similar effect. Refrigerants obey specific pressure/temperature relationships for phase transpformations to occur. If you are significantly underchargeed, the compressor will not devleop enough pressure in order to allow the charge to condense in the condenser. If this happens, heat transfer cannot take place as you will have no vaporization to absorb heat. At the very least, the heat htat can be transported is a function o fhte mass of refrigerant undergoing the phase transformation. If you have 30% of teh refrigerant present, then (if it works) you will have 30% of the system capacity.
If, on the other hand, some yahoo throws his refrigeration tables to the winds and overcharges your system, you will reach some phenomenal pressures, and you will probably have some really spectacular leaks (about the time a slug of liquid that can't evporate because the system pressures are too high returns to the compressor) -- I would not advise opening the hood with the A/C running.