R134a A/C conversion, need advice.
 

I finally got my A/C system blowing from the right vents (stupid dead vacuum line), but it's still not blowing cold air. Since everything seems to be in good shape mechanically (I've been over this system pretty well) I'm guessing that it's just low on freon (last added in 1998, judging by the vacuum line it hasn't been used since at least 2001, probably closer to 2000).

Since refilling the system with R-12 isn't really an option, and since R-22 (which is compatible with R-12 fluid) is much too high pressure for the compressor, I'll have to convert to R-134a. Aside from replacing the receiver/drier, evacuating the system, and changing the compressor oil, what needs to be done? I'm assuming that this is something that I can do myself given a weekend?

Anyone who has done this before I'd like to know what kind of effect this has on the A/C system's ability to cool the car.

Thanks a lot.

Aaron

I had a shop convert mine....

Cost about 150 U.S (225 canadian).

Its cool but on 100F day its not as good as the r12 i had in it in the 90's.

Done a few...Sometimes not necessary to change out any parts. Interdynamics makes a conversion kit. But, there are a few things you should know. First, the system has to be properly emptied amd tested to assure there are no leaks. Second, the inlet (low pressure side) fitting is damn close to the alternator bracket. I have had to use a Dremel grinder to relieve the alternator bracket a wee bit and install a 90 degree fitting for the inlet. Do the grinding before changine out the fittings and clean the aluminum dust off everything to avoid internal contamination. The kit I spoke of includes a sealer, the necessary oil, etc. Follow the instructions and you should be OK. But get the system evacuated professionally first (and leak tested). And, never try filling the system from the high pressure end!! Severe injury can and will happen.

No affiliation with Interdynamics, just a happy user.

EPA certified

Forget the R134 conversion unless your going to purchase a new evap core.

R12 is still very readily available, it's about $19 a pound and you will thank yourself later.

The problem with R134A conversions and 944's is this, you already have a complex cooling system that keeps the car cool when it is perfect working order, now you go and convert to 134A. The 134A takes a higher pressure charge to give you the same cooling effects on your R12 designed system.

This causes two problems, the first is with R12 you get 43 deg vent temps in the 944, R134A sits around 47~48 and sometimes 50, thats not great on a 95 deg day. Face it you have a small core condensor and tubing that was designed for R12, 134A takes a larger core and larger pipes to give it a higher pressure charge.

Secondly your system works harder, robs more power from the engine via the compressor, and here is the best part yet, you are transfering more heat to the condensor, and thus blowing hot air through your radiator at driving speeds.

So you shouod purchase a new "parallel flow" aftermarket condensor, new fittings, and new O-rings ( since esther oil does eat the 944 orings out,) and a new condensor.

Or you could just get it recharged with 3.5 cans of R12 for around $75.00 with labor.

Scott R.
I agree with you 100%. I didn't want to be the first to explain this retro-fit problem, since last time I received mucho flaming. One other point that you left out is R134A leaks out much easier than R12, due to the higher pressures/temps, and molecular size. A proper R134A retro is not always cheaper when you consider the additional items needed to make it perform as well as original.

If you want to do this conversion then I suggest you check out FR Wilk's web site http://frwilk.com/early944/ and go to the AC "r134a" link. He has the Porsche factory AC134 tech bulletin for this procedure. I also suggest you get the Haynes automotive AC manual. Great resource.

With respect to Scott R and Wolf1, this is an effective upgrade, just not as good as R12. It won't blow as cold so it's probably not recommended for the hot southern States. But you (we) should do OK in the north.

Through some exhaustive research I suggest you change (along with the mandatory stuff like dryer and service fittings) the compressor to an aftermarket like Sanden and the expansion valve if your system had any damage to it. The compressor because the original Nippodenso will blow a seal with the higher pressures of the 134. The expansion valve because it has a tiny orifice and if there is any debris in the system then it will clog.

we did it, asked a shop about it, they said all we had to do was drain it and re-fill it with r-134a. Nothing with the evap core. It runs fine and we have 42 degree a/c...

Last time I priced R12 it was more like $125 a pound. The 134A is not as efficent as R12 and it doesn't work as well. Thats why it wasn't used earlier. Some dryiers are not compatable with R134A, but the type used on the early 924's is compatible. I would think the 944's would also be compatable. The Interdynamics Kit works well buy it and try it out some of what you are reading here is not correct. Here is what I found doing my conversion.

Also there are oils that are compatable with R12 and R134A dont worry.

Having the system purged and check for leaks cant hurt but it is not necessay.

Do not use the pressure chart for R134A. Your R12 system was never designed to handel those pressures. R134A pressures are dependant on the engine compartment temp. Buy the pressure gauge when you buy the conversion kit. For a conversion I would reduce the recomended pressure by 20%. This will also reduce the effectness, but we are talking about a fix that will cost less than $50. If you want to spend hundred's go ahead.

A larger evaporator core would help, so would a larger compressor and condensor. It is not necessary though I may buy the larger evaporator core. I live in Florida and when it gets really hot the R134A is alright if I put all the vents on me but in stop and go driving if I have to share with a passenger its not quite good enough. If its cooler, say in the evening or for highway driving its good.

R134A does not leak out quicker. The leaks are created or made worse when people try to use R134A pressures and then the R12 system is over pressureized.

R134A does not require larger tubes. The amount of cooling in the evaporator is determined by volume, surface area, airflow over the cooling surface, and the state and temp of the R134A when it enters the evaporator.

I am not sure but I would be suprised if the ester oil eat seals. It does not make sense that a manufacture would produce a product that would destroy the seals. Most seals break down when exposed to oil and all seal's break down with time. Its been two years and my seals are fine. Its more likely that when the system is overpressurized the seals blow.

Molecular size is probably different, but it doesn't make sense R134A is converted to a liquid state by the compressor. Well almost our R12 systems will not handel the necessary pressure to fully convert R134A. It is then converted into a gas and it get's cold. All A/C systems leak but I do not think give or take a few molecul's will make it leak that much faster.

$19 per pound for R-12? What have you been smoking? Last time I priced R-12 it was $60 per pound and climbing. If you can point me to a place that will sell me R-12 at $19 per pound I'd stock up like you wouldn't believe. I could make such a profit on that it's not even funny.

I'm gonna go with Roger on this one, since his advice mirrors the advice of three ASE certified mechanics I've talked with outside of these forums.

To the person who said that the original NipponDenso compressor will blow if I switch to R-134a, it will only blow if I'm an idiot and put in 30 ounces of R-134a. At most I should put in only 85% of the amount of fluid when using R-134a. Do not put more than 25.5 ounces of R-134a in the system, or you will over-pressurise it.

Aaron

I am ASE certified (which really means almost nothing these days,) and I also have a A/C license. If you paying $60 lb for R12 than shame on you. I just purchased two pounds for a Maxima I was working on the other day for $19/lb.

I suppose $60 may be the "end user" price somewhere.

Now on to "blowing the compressor." I would put money on the fact that you will loose the front compressor seal "quicker" than if you were using mineral oil and R12, I did and it was an expansive mistake.

On to "ounces of R134A question," don't go by ounces, go by charge. You should have about 35-40 on the low side and 135~140 on the high. You add until the pressure is correct and the vent temperature is as low as you can get it.

Since my R12 source is a local NAPA, here is a link to an EBAY auction for 12 cans with a "buy it now" of $250:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2406968034&category=67 65

Hmmmmm 250 divided by 12 is.......

Yeah, I kinda fell on my face there. Found a site with a case (12 pounds) for sale at $280.00. Which is $23.33 per pound. I suddenly feel very much taken by my mechanic. I believe that this year's tax refund is going to go towards purchasing a case of R-12.

In the future I'll do my best to double-check things before I say something.

Do most NAPA stores sell R-12? I understand that one would need an EPA certification to purchase the R-12, but I have a friend who is EPA certified for HVAC and who could get the R-12. If most NAPA stores do stock R-12, do they sell in any quantities less than a case and does one need any kind of forms or authorization aside from the certification to get the R-12?

Aaron

My 3 yr old R12 944 cools like ice compared to my girlfriend's R134 968 that was converted by the Porsche dealer last November.

Very good Scott

I never thought about buying R12 on Ebay. I would not have converted mine if I was aware of this. The local shops charge alot more, but then again I bought a $600 ECU off Ebay for $26.

Stick with the R-12 if you can. I bought 2 1,000# cylinders @ $23,000 each 5 months ago and I'm sure the price has gone up abit since. Check Ebay for the small cans or cylinders.

ch944