don't use r134a. use HC-12a or similar brand (hydrocarbon refrigerant)
i recommend getting duracool as their cans come with the oil already in it so be sure to shake the can up real good. if its been sitting for a real long time you might need to run the duracool duradry or pull full vacuum for a few hours, or replace the receiver drier. then use duracool a/c oil chill can and make sure you shake the poop out of that can to get the oil to come out right.
for a passat mk3 i found a site that recommended approx 2 cans of the duracool (i did the math, but dont remember the hard numbers) but what you really need to do is just use a thermometer in the vents (i think the achievement is 40F) and buy the duracool charging hose and 2 cans with the other duradry if you need it and a/c oil chill if its been sitting dry for a while. they also sell duracool system seal that can actually seal pinhole leaks in the system, but most of the time its actually the schrader valves that leak, so when someone hooks up their machine to your car, it seems like theres no leaks, but when they take their hoses off, it slowly leaks out there. this can happen especially if the system has been overheated, due to the rad fan quitting. one thing i never understood is why they don't have a refrigerant high temp shut off switch... they have a high coolant temp a/c shut off though. the high temp refrigerant temp shut off would save people a lot of headaches and having to recharge their systems...
so back to the charging procedure. the instructions say to hook up the charging hose to the low pressure side (you can't mix the two up as there is a size difference) first off, find the pressure switch harness and get something to bridge the wires (you might need to do this, or you might not. leave it connected for now but be ready to bridge it in case) now start the car and put a/c on full. with the charging hose hooked up to the low side, and the can hooked up to the charging hose, puncture the can with the twist valve, and then invert the can and slowly unscrew the valve and watch the gauge carefully. when the pressure reaches the blue, screw the tap in to stop the flow, you might need to wait a little bit for the pressure to equalize in the system so the pressure switch kicks the a/c clutch on. charging my system i didn't want to wait so i just bridged the connection myself and the compressor sucked the refrigerant through the system. all i did was charge my system up till the gauge was at blue and the compressor was on. when the compressor is off the gauge will read quite a bit higher though, so don't get tricked by this. i think the compressor cycling once every 2-3 minutes is okay.
the first can is crucial as you might find that you have a leak somewhere. don't start with the second can if you hear hissing or start losing pressure or cooling. you also need to make sure that the rad fan turns on with the a/c. if it doesn't, then you need to take care of that first. i had to change an o-ring on my system because it was totally destroyed by the heat... you might need to do the same.
now on to the benefits of duracool or other hydrocarbon refrigerants. r134a is a blend of gases with one of them having a very small molecule. this molecule can leak out of a system which would normally hold r12 or HC-12a just fine, and leave the rest of the gases in the system, making it seem like there isn't a leak but a greater problem. HC-12a has a bigger molecule than even r12, so the likelyhood of leaks is greatly reduced. with r134a a recharge isn't just taking a can and topping it up. the whole system must be evacuated, and fresh refrigerant installed. this is because of the small molecule that likes to escape. with HC-12a, you can simply top up at anytime if you have a minor leak. there's also lower compressor head temperatures, so your whole a/c system should last longer, with lower pressure needed than r134a. but just remember that its most likely the charging valves if you have a leak
hope this helps you
i just fixed my sisters a/c for her bday and she was very grateful. her pt cruiser rad fan low speed quit on her, so i installed a resistor going from the low speed to high speed, and it works great now with the duracool
i can even describe the events that took place for her a/c system to stop functioning. a hot day blew the internal resistor in the fan, so the high speed worked (so the engine wouldn't overheat, but come pretty darn close) but the refrigerant did overheat and started leaking out anywhere it could. the pressure switch cut off the a/c when it got too low, and whamo no a/c. this is why a high temp a/c cut off switch would be such a great idea.
either that or an indicator light for the rad fan being broken, but i like the auto shut off just in case someone doesn't pay attention
Topic: Air con recharge MKIII (Read 5212 times)
