Macallan21

When I first got my car in July 2009...it really annoyed me when the car would control the AC because it'd cycle from no air flow at all (or a dose of outside air) and when the temp got above the setpoint, it'd blast me with ice cold blasts of air (since it controlled the fan speed too).
Felt like I was having hot flashes or something.

Got in the car today, and it was 90F outside, and while the AC air is still cold, it's not as ice cold as it was before.

Has anyone done an AC/refrigerant recharge? Is it as simple as going to Autozone and buying the can with the pressure gauge and refilling it to a certain PSI?

Moviela

No. It is not that easy. You need a vacuum pump to pull down the system to remove any moisture from the system. At the same time you need to make sure that the vacuum holds, meaning no leaks in the system.

You then need to charge the proper amount of HA134 by weight, and verify the low and high side pressures are correct.

Of course you need a manifold pressure gauge set, and to follow the rules a recovery system for the used refrigerant.

You would also need VAGCOM to examine the temperature and pressure sensors for correct operation.

A quality shop is well worth the price to have it done.

jagtoes

It is a pretty simple task if you are only low on freon. You 1st need to see if the system is low and that requires a gage to take a reading . The cans you buy at Autozone that have a gage on them will do the trick.You just need to plug the can into the LOW pressure port with the car idling at around 1500 rpm. Check the gage and if it is in the normal zone then you need to look at other areas as the problem. If at 0 then you have a major leak and you'll need to get it serviced. If down slightly then you have a slow leak which could seal up with an AC leak sealer. If not you need major service.You only need to vacuum down the system if you open it up to fix or change components .

Moviela

If your car is low on Freon, your system is open. Freon is not consumed as long as the system is closed.

Adding Freon to a low system is acceptable for testing purposes, but your car will suffer "the black death" from aluminum oxide if you allow the system to run very long with air inside. The fix then is to change ALL the components touched by the refrigerant.

It is better to fix leaks than to depend on sealers. There is no mechanic-in-a-can. I will use ultra-violet dye to find leaks if a vacuum will not hold and the usual suspects don't have any signs of leaking.

dscline

Technically, all automotive HVAC systems are open systems. The shaft seal is not a perfect hermetic seal. It is normal for trace amounts of refrigerant to be continually lost. If his AC is still running and producing even slightly cool air, then there's enough pressure in the system to satisfy the safeties, enough pressure to create at least some refrigeration effect, and enough pressure that there shouldn't be air in the system. As long as the pressure is positive relative to the atmosphere, refrigerant will continue to leak out, not air leaking in.

But while I don't believe it's necessary to vacuum down a system that still has positive pressure, I would still take it to a shop that has the proper equipment to accurately charge it. The bigger danger is overcharging the system. The simple act of adding too much refrigerant can change saving $75 into costing > $1k.

jagtoes

I guess I assumed that everyone would know if the system was still under pressure that NO air was getting in. If the system has 0 pressure then there would be moisture in in it and would need to be vacuumed down after the leak was found. I guess I'll have to be more specific in the future.

Moviela

According to the SAE Audi loses less than 14 g/year. That is about half an ounce. The greater portion of the loss is through the pores in the hoses, not the shaft seal. Audi has the compressor manufacturer perform a 100% helium leak test. If helium can't pass the refrigerant does not stand a chance.

dscline

As I said: It is normal for trace amounts of refrigerant to be continually lost. I would consider < 14g a year a trace amount. The point remains: just because refrigerant manages to leak out of a system doesn't mean that air has leaked in. As long as there is significant positive pressure in the system relative to the atmosphere, air will not leak in, refrigerant will leak out. Just because he is a little low on refrigerant (which we don't even know for sure) doesn't mean the system needs to be evacuated. IF he does have a leak large enough to warrant repairing it, then the repair will likely require an evacuation.

After four years he still has enough refrigerant to cool, even if it's not cooling as well as it did when new. So if he has a leak, it's not a huge one. These have fairly small refrigerant charges, a relatively small loss of charge can affect performance.

Macallan21

OK!

The car still makes plenty of cold air. I don't have a system leak. I think I've just lost a bit of refrigerant over the last 4 years.. which is NORMAL, and was wondering if I could top it off with the can. and it looks like if I check the pressure and it is low, then I can top it off with the can. That's all I needed to know.

No need to vacuum down the system or anything else silly and intensive right now.