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Conversion to R134-

Just converting my 1988 944 to R134A.

I had the R-12 removed and recaptured by a trained professional.

I installed the new adapter to the low pressure side and slowly approached 25psi, slightly after 25psi, the compressor kicked on and pressure indicator jumped to about 50 psi. I'm getting no cool air at this point.

Suggestions.

ST

Old 06-22-2010, 12:07 PM
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I believe you need a new compressor and receiver/dryer that is R134 compatible. Just changing the fitting is not enough, I don't think.
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Old 06-22-2010, 03:15 PM
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ST,
First, its nice that you had the R12 taken out by a professional shop.

I have no idea what part of the country you live in, but why remove R12? If your system was still holding a charge of R12, many people would think your crazy to switch to R134a.

But since you have decided to convert, you can use the old Nippondenso Compressor on the '88.

Steve is correct that you should replace the receiver dryer.

The R12 oil should have been removed from the compressor and Esther oil or PAG 46 should have been added---2 or 3oz.

What is important is that the system needs to be vacuumed 90 minutes or so with a "real" vacuum pump, 2.5cfm or larger.

Properly attached AC guages will suck the first can of R134a immediately and you can put the second can in a pot of warm water to aid the final fill---MAX 24 ounces. You do not put in any more.

GL
John
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Old 06-22-2010, 04:36 PM
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Where exactly did you install the "low pressure fitting"??? On this car the low pressure port is actually on the compressor right where the hoses connect to it and it is a real ***** to get to. If you installed the fitting on the line near the driver's side strut tower then that is the "high pressure fitting" and you don't have anywhere near enough refrigerant in there. I don't know why, but many of the common "low pressure" conversion fittings thread right on to that high pressure port.

I'd also suggest picking up a set of manifold gauges. Harbor Freight sells a set for $50.

Harbor freight also sells a cheap vacuum pump that is powered by compressed air from your compressor for something like $15. It's crap, but it gets the job done. A "real vacuum pump" (as John put it) would be better but also a lot more $$$.

I disagree with the "24 oz max" statement. I needed to put 3 cans in before it would cool the car down on a hot Florida summer day. My advice is get as close to the max pressure specified by Porsche in the shop manual without going over. I don't have the manual handy or I'd give you those numbers.
Old 06-22-2010, 05:17 PM
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Quote:
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Harbor freight also sells a cheap vacuum pump that is powered by compressed air from your compressor for something like $15. It's crap, but it gets the job done. A "real vacuum pump" (as John put it) would be better but also a lot more $$$.

I disagree with the "24 oz max" statement. I needed to put 3 cans in before it would cool the car down on a hot Florida summer day. My advice is get as close to the max pressure specified by Porsche in the shop manual without going over. I don't have the manual handy or I'd give you those numbers.
OUCH

If you buy the "crap" vacuum pump, you may soon need a new compressor after the 90 minutes of required vacuum. Normal "garage" compressors will not take the work and the pressure will drop from 120psi to 90psi to PPPPFFFFTTTTT

R134a should be 70% to 80% of the normal 30-33oz charge of R12.
Thats a fact. You may waste 3 to 5 cans, but for best cooling, 2 cans max-24OZ +- an oz installed.

John
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Last edited by John_AZ; 06-23-2010 at 06:22 AM.. Reason: Corrected R134a capacity to 70% to 80%
Old 06-22-2010, 05:55 PM
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I would not fill with 134... Its on its way out just like the 12.... I would leave the 12 in honestly.....
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Old 06-22-2010, 06:37 PM
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Here's what I've come up with. The early cars and 924S have the same capacity, 40.6 ounces of R12, conversion to 134 would be a charge of roughly 2.0 lbs. That's 32 ounces.

The others (later 944's and 951's) have a smaller capacity, I think it's roughly 2.1 lbs. Therefore the correct charge should be 27 ounces of 134.

Keep in mind that efficiency is determined by pressure, which is heavily dependent on ambient temperature, especially with 134. It's 92 here right now. The perfect pressure for me is 28-30 low and 220-225 high. This is at idle, mine does not idle up when the a/c is on, I hope it never does.

After 20 minutes of letting it do it's thing, the inside cabin temp on the horn pad was 55 at idle, the vent temps were mid 30's, 34-36 degrees. It's a 134 system with the original drier, some of the same oil and a new front seal on the compressor.

I can't imagine why those pressures would not work well most everywhere. There is one thing to keep in mind, clean the condenser, it cools the freon which a very important factor in the performance of the system.
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Old 06-22-2010, 06:40 PM
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Sid, I did more research which revealed that only the EU is mandating HFO1234yf by 2012. We won't see it probably until 2015-16 with mandates no sooner than 2019-2020.

The thing about 134 for us is that the manufacture of R-22 (HCFC) is done in the USA and home a/c technicians are looking to 134 as a replacement. It drives demand up, and supply has been cut by 134 manufacturers. It's no different than what has happened before. The prices are now going through the roof. Sam's club has the best deal on jugs and cases of cans. That is unless you find someone offering a great deal to a shop on a promo deal.

John, I live by the 80% rule of thumb and play from there. It's much hotter there though. It's all about pressures.
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Last edited by mattdavis11; 06-22-2010 at 06:54 PM..
Old 06-22-2010, 06:48 PM
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Thanks for all the responses. I'll try adding to the port down by the compressor today and see what happens. I figured the Germans would put the refill port where it was easy to get to. The port on top of the driver's side strut appears to be in the same line as the sight glass and the drier but my bifocals sometimes fool me. I'll look a little closer.

I'll let you know how I come out this eveing.

ST
Old 06-23-2010, 05:45 AM
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Quote:
Originally Posted by mattdavis11 View Post
The thing about 134 for us is that the manufacture of R-22 (HCFC) is done in the USA and home a/c technicians are looking to 134 as a replacement. It drives demand up, and supply has been cut by 134 manufacturers. It's no different than what has happened before. The prices are now going through the roof. Sam's club has the best deal on jugs and cases of cans. That is unless you find someone offering a great deal to a shop on a promo deal.

John, I live by the 80% rule of thumb and play from there. It's much hotter there though. It's all about pressures.
Matt,
Thanks for correcting me. I edited my post to say 70% to 80% of R134a in a converted R12 system.
Your daily experience working on a variety of cars and trucks is far greater than my limited knowledge of just the Porsche 924S/944 and my '98 Cherokee.

About the price of a 12oz can of R134a. Last year WalMart was $6.79 a can. I went in recently and now it is near $10 a can.

John
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Old 06-23-2010, 06:21 AM
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My capacity in the '88 924S---



John
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Old 06-23-2010, 06:27 AM
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I'll be, mine's 40.6 oz. I have to yield to the greater knowledge on capacity. I thought I read the later 924's had the same system as the early. Wrong. I'd take a picture of my sticker that looks like John's, but I'm too lazy today.

You guys have the 10P15, or is it a 10P13?

John, I was amazed to see it $7 a can at wally world here. It's $9+ at the local parts stores.
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Last edited by mattdavis11; 06-23-2010 at 06:49 PM..
Old 06-23-2010, 06:46 PM
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OUCH
I don't mean any disrespect man, just sharing my experience.... even if it is contrary to the conventional wisdom. All I know is I can make ice on a 100 degree day.

Spec says:
0.5-2 Bar (7-29 psi) on the low side
10-20 Bar (145-290 psi) on the high side

Last time I checked I believe I was somewhere around 32psi on the low side and 270ish on the high side.

The Harbor Freight pump I have Air Vacuum Pump with R134A and R12 Connectors is currently on sale for $8. It requires 4.2 CFM @ 90 psi. My 12 year old Craftsman 5.5hp compressor is rated for 6.4 CFM @ 90 psi. I consider my compressor to be "below average" for a garage compressor but everyone will have their own opinion on that issue.

For comparision, a "real vacuum pump" from Harbor Freight Two Stage 3 CFM Air Vacuum Pump costs $150. There is no doubt this is a better pump than my $8 cheapy, but they both suck!
Old 06-23-2010, 07:09 PM
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Low Side

Thanks to the clown, I found the low side and pumped in some refrigerant and when the compressor kicked on, I got a pressure drop as desired and then I pumped on up to about 35 psi. I only consumed one 10 oz. can of refrigerant to do it. I suspect that I need to purge some air off the high side. I haven't checked for bubbles in the site window yet but suspect there will be a few. I lost a day here painting a bathroom for my daughter so tomorrow is second coat day and AC purging.

What fun this has been. Endothermic, exothermic, Boyle's Law and long discussions with the pneumatisist from propulsion systems.

Tomorrow, more test reports.

ST
Old 06-23-2010, 09:33 PM
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(I put it in the color green to mean foolish sarcasm)

I did see that HF had the 2.5cfm vac pump on sale recently for $59.99.
The 3cfm is a 2 stage---more than I need for a few uses.

I have a pair of the venturi --suck pumps. One has only the R12 fitting, the other has a combination R12 and R134a. My compressor could not keep up the pressure. I am going to make use of them for another purpose---eventually

John
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Old 06-23-2010, 09:44 PM
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. I haven't checked for bubbles in the site window yet but suspect there will be a few. I lost a day here painting a bathroom for my daughter so tomorrow is second coat day and AC purging.

What fun this has been. Endothermic, exothermic, Boyle's Law and long discussions with the pneumatisist from propulsion systems.

Tomorrow, more test reports.

ST
Unless I have inhaled too much exhaust, R12 has bubbles in the receiver dryer site glass.

R134a does not produce bubbles! It will always look like a stream of fluid.

John
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Old 06-23-2010, 09:53 PM
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Thumbs up R-12 and location

I moved to R-134 because of cost and availability. Also, I used to work on the instrument that measured the amount of ozone in the atmosphere. It was called a Solar Backscatter Ultra Violet (SBUV). It rode around on the shuttle originally and later was put on satellite platforms. Ozone bounces back the ultraviolet range of light radiation, so if no backscatter, no ozone. It was probably one of Al Gore's first attempts at revenue generation but I think that he's done better (until recently) with global warming. I suspect that his globe is currently cooling.

I'm currently living between Denver, CO and near Yellowstone Park, WY. We can probably drop ambient pressure out of the equation because we have a closed system but ambient temperature has to be a factor. We get some 100+ degree days but not too many. The AC is not a big issue as I usually route thru the mountains. If I blow it, I'm looking at some weight reduction and better performance on the mountain passes. I've been approaching a race configuration on this car for almost 20 years now. As things fail, they get dropped off if they are not critical.

I was surprised by the cost of a 10 oz. can of the refrigerant. It has really gone up since I last did this on a GM vehicle some years ago. I paid more than $10 at Walmart for the stuff. The GM system has really held up well though, post conversion.

I was curious about Nippon Denso. It would appear that they make fuel injectors for both Ford and Bosche. I wonder if a Ford injector will work in my 944. I suspect it would be cheaper than Bosche.

Any of you guys know where to look for the control unit for my cruise control? It's supposed to be a small silver box mounted above the hood release lever in the driver's boot. That's the next issue. Will it be cruise or weight reduction?

ST
Old 06-24-2010, 04:18 AM
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What became of the oil issue? Isn't r134 incompatible with the standard r12 oil. I know mixing oil from the different systems is definitely bad (acid sludge). I can't remember which r134 oils would do that, but one half of the equation needed for disaster is the type used exclusively in r12 systems.
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Old 06-24-2010, 10:24 PM
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I've been testing and operation seems to be where I want it. Low side psi is about 40 and air temp is where I want it coming out of vents. My thermostat is shot for hot and cool control so I just want to be able to leave the compressor switch on and get some cool when necessary. It is comfortable at 85-90 degrees. I think the air to refrigerant ratio is not correct but it works for me. Thanks for all the help guys and gals.

ST
Old 06-28-2010, 12:08 PM
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my high, and low pressure ports are on the drivers side shock tower.

Old 06-28-2010, 02:49 PM
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