Hi all,

So I took my slightly leaky 968 (coolant; very small leak; still need to diagnose) for a spin today only to immediately realized the AC is not working at all. The electronics appear to be engaging correctly, but I am getting marginally warmer than ambient air funneled into the cabin. I did a quick check in the engine bay to ensure the compressor was actually running. It was not. Some quick searching shows this is a common issue when the refrigerant in the system is low (a low pressure valve prevents the clutch from engaging...?). So I would assume a recharge would be in order.

However, the previous owner noted the AC system had been upgraded to a modern refrigerant (I think this would be 134a from R12?). Unfortunately, I am not sure what this upgrade consisted of. I have two concerns, what was likely to have been changed and what might already be an issue since I believe this was done approximately 12 months ago?

I have never had experience with maintenance of an AC system, so pretty unsure where to start. If I take this to a Joe Shmoe car shop, can I get the system recharged? Should I even attempt a recharge without further diagnosis? Is the 968 exotic enough Joe Shmoe will not be a good choice to touch my AC system?

Any help would be appreciated!

I still love my first Porsche, despite its leakiness and malfunctioning AC

- Nate

 

You probably are not getting compressor clutch engagement. You can start with verifying this. If the compressor clutch does not go'click' and the compressor does not turn with the belt, then you can start from there.

Checking the system pressure is a good next step, there is a pressure switch that prevents the system from operating if the pressure is too high or low. Usually the pressure is low due to a leak and the system disables itself.

The relay can also fail or the dash switch, or the fuse, but the first two checks are worth looking into, possibly on your own if you feel like it. The low pressure side port on some 968s is under the car near the compressor, so not super easy to get to. If the system has been converted they might have swapped it over to R134A style ports.

-Joel.

 

Joel has all the right points to follow.

If the compressor is not working, I would bring the car to an AC specialist. One that just does AC work. If you need the electrical schematic for your car, we can give it to you so it can be printed out and given to the shop.

If it was low on refrigerant, what they would do is use a vacuum pump to evacuate the charge, weigh it, then recharge it with the proper charge by weight. I don't know what the 968 system charge is, but probably about 500-600 grams. It should be on a sticker under the hood.

Let us know if you need the electrical schematic. I can post it.

 

Thanks for the feedback guys.

I have confirmed the compressor will not engage, but I believe it is "clicking" when the AC button is pressed. I spoke to a friend who noted he has heard of similar issues on R12 to R134a converted systems in that the R12 seals do not work well with R134a resulting in substantial Freon loss during cold months. Sounds spot on for my situation. As such I will be looking to recharge.

Any reason I wouldn't want to just go for a self recharge kit and top up myself?

- Nate

 

You could go with a self recharge kit if you can get access to the port, and the R-134a can fits onto the fitting. I have not done it personally, but it was stated it's hard to get to it. Then you have to put the can on the low pressure side while the engine/compressor is running.

You are not evacuating the system (which you want to, this is good, removes all the moisture), and you are not measuring the amount of R-134a that is being put back into the system.

Considering you won't be getting rid of a 968 as you might a daily driver, I would not recommend this way.

If you go to an AC shop, they should charge about $150 for the service. Just had it done on my Audi S8, it was down to 300 grams on a 660 gram system. The compressor would come on, but not do anything.

Spend the few buck and leave it to a professional. Good luck!

 

You have very little to lose by trying to top off the system with a cheap can of r34a. I did the change-over on my 944S myself and I have to top it off with a small can every year. I did have a buddy that runs an A/C company put the system at a vacuum before I started the change-over, but thats not necessary to do again unless your systems totally leaked out. The new R34a ports should be in place from the change-over so just buy a can and give it a try.

 

You should first determine if the compressor clutch is clicking on and spinning the compressor. This can be done just by looking at it and cycling the AC switch on and off a few times. If you think the clutch is indeed clicking on but the compressor is not turning, that is pretty bad news but unlikely. If you are hearing a different click, who knows.

If the compressor is turning when you hit the switch, see if it stays turning or if it stops after a short time.

If you just try to charge it without knowing if it's already full or not, lots of stuff can happen. One can is a lot and you can easily overcharge the system. Maybe it's already overcharged. You might have an electrical problem or a heater valve problem and your refrigerant level could be fine.

Personally I would get a gauge and check the pressure, if it is low you will need the gauge anyway to see how fast it leaks down again. You can check pressure on the high side but trying to charge from there is real bad.

 

So I am a little torn on getting a professional to look at this, primarily because I am mechanically inclined, the local AC repair shop has a questionable lot and I don't want them to handle my baby, and this seems like a potentially yearly thing I will need to do if the system was recharged just 12 months ago.

I have identified the fill point, seems like a pain to get to, but doable. With a gauge, I should have no issue filling the correct amount of refrigerant. My only real question is with regard to the oil. Can you "over oil" the system? Seems like you wouldn't be able to. If you added too much oil, I would think it would just degrade the capability of the system, not damage it.

If that is the case, why not dump a proportional amount of oil into the system, as I fill up with R134a? I think the ratio is 16:5oz (can't recall the sticker in my engine bay, but I think it is listed).

- Nate

 

Nate:

I don't think you'll have an issue. I have done this is my old Audi many of times. It had a tricky valve and you had to jump a switch, which you probably won't have to do. But here is my procedure which is titled "Poor Man's AC Recharge"!

http://forums.audiworld.com/showthread.php?p=15572065

 

Paul,

I think I am going to give it a shot myself!

Anyone see issue with my intention to try to top up with a proper ratio of oil to refrigerant? I am thinking 1oz oil in, then ~ 3oz refrigerant until I am at the correct pressure (I am assuming this pressure is universal for all r134a systems...?)

- Nate

 

I would not add oil unless you drain out a significant amount of oil by taking stuff apart or totally venting.

 

First problem. Most likely your original R-12 fill port was not swapped out to the R-134a type. So, when you get the can of R-134a and the small hose and gauge, you'll likely find it will not fit the port on your car. Have no fear, there's an adapter fitting at Napa just for this purpose. Take your car with you, and have the Napa tech look at the current fitting. In may have been changed, but prolly not.

Now you have the fitting on the R-12 port and the R-134a can of gas to charge it with. The can of gas you got has oil with it. The next problem is are you sure it's changed over, and was it evacuated and cleaned of all POE oil from the old R-12 days? Does it still have POE oil in it? If so, and you add the charge can with PAG oil, you're going to eventually get a gloppy mess as the PAG oil will etch out the system and the Ester in the old oil will gel. Not good.

Finally, when you start charging the system, eventually and hopefully the low pressure switch will close, and the comp will start spinning. Before you get this far, here's a suggestion. Test the compressor clutch before filling. Take a jumper wire from the + terminal of the battery, feed it over to the area where the comp wire is, and disconnect the comp clutch wire from the harness, and jump it to the battery using the jumper wire. You should hear the comp clutch 'click' into place. Remove the jumper, and start the car. Now carefully, jump the comp using the jump wire again and check for the comp clutch engage, and the comp spinning. Note any serious grinding noise, this would be bad. If it doesn't grind, remove the jumper quickly so you are not running the system dry. Turn off the engine, reconnect the comp clutch wire to the harness, and start filling.

Hopefully the relay, and the button and the low and hi pressure switches are all good, and the comp starts when the low pressure switch closes. Watch the gauge on the can(some are on the hose in-line), and fill by shaking the can while holding it sideways. Have your recirc on, and the fan set on high. I like to have an aux fan in front of the car blowing air into the grill, but you can get away without that. Work in evening or morning when it's cooler so you get a good charge fill.

When you get into the green range on the gauge, check the temp of the air coming out of the vent. It should be in the low 50s, or high 40s in deg F. If you have a meat thermometer, stick it in the vent, and it should be in the low 40s or high 30s on a modestly cool day(under 78F outside). Keep filling until the gauge reads near the top of the green range on the gauge. Hope your hi pressure switch is set right, and that it will support the higher pressure that R-134a uses. If the comp shuts off as you fill, you've gone over the pressure rating of the hi pressure switch and you'll need to discharge some of the gas out the port. Remember, pressures go up when it's hotter outside, so don't overdo it.

If it's been converted right, that should be it. Look under the hood, near the fill port for a sticker that says it was converted to R-134a. If you don't see a sticker, add one so that others will know.

If you don't want to get involved in all this, take it to a AC shop, have them tell you what kind of refrigerant is in it. If it's R-12 do NOT let them evac the system! Keep as much R-12 in as you can, and ask around for a shop that will fill with R-12. If it's R-134a converted, have them evac it, then pressure test with Nitrogen, and see if they can find your slow leak. It's better to fix these unless it's the comp seal behind the clutch(common). Most comp need to be replaced if the front seal goes out. Sometimes it's just the fittings or o-rings in the system and they can locate it with a spritz bottle of soap. Some places use a dye injected, and a black light to detect.

Personally, since I live in TX and we gotta have AC, I take my cars to a guy I know that does Porsche AC. Get it fixed right one time, and you should rarely have to fill it again. To keep it in good working condition, drive or start the car once a month and run the AC on max so that the seals and o-rings will be maintained(including winter).

 

The O'rings typically are different on a r134a. Besides that the rest should not need changing.

 

Thanks for all of the detail. I did find a sticker in my engine bay showing a conversion occurred in 2001. I must have misunderstood the previous owner when he mentioned work on the AC; I assume now he simply recharged it a year ago. I have a "AC Pro" all in one can that I am going to give a shot sometime in the next week. Wish me luck!

- Nate

 

Excellent news. That means the system has been flushed and you have the right oil in. The can of AC pro should top you up nicely. If you have a fan you can put in front of the grill would make it better. Work in the morning or evening to get it fullest.