Converting A/C R12 to 134a
 

Just wanted to start a thread on anyone who has done the change over and what was involved, some of the issues, what were the results. I'm looking into doing it to my car which is a 1981 928. http://forums.pelicanparts.com/uploa...1277860279.jpg

I bought a kit.
I had it professionally installed.
It worked fine initially.
About 18 months later it stopped working, with a bang.
I haven't diagnosed it yet.
Others have advised some replacement compressors are not too stout.

At the dealer if we did a conversion, everything got replaced. Never had one come back.

Hi Brad,

Did you use a Griffiths kit with the Kuehl compressor?
That is what was used in my '90 GT. I didn't hear the rumors of issues until after mine failed, unfortunately.

Sorry Stan I should have been clearer.
I am a GM mechanic and when they took R12 off the shelf the only way we could help the customer was to install the 134 retro kits. I believe the were a delco retro kits and came right from GM. they were very costly somewhere around $3000.
The comp, drier, evap and condenser and lines were replaced due to the oil can not be mixed and anything that stays has to be flushed.

R12
 

If you can get R12 then i would suggest you use it. I know it is VERY expensive however. I am converting my system back to R12 from a po conversion to 134.
12 is significantly colder than 134 and provides longer life imho.

I have heard that there is a substitute that will work in the R12 system.

I went through this change over twice. First was on my dad's 85S and the second was on my 87 S4. What I did was remove the AC condenser and flushed it out with AC safe which got out a lot of the old R12 gunk as well as the mineral oil (mineral oil will not mix with r134a oil). I also recommend you install a new receiver/dryer and expansion valve. I would also remove the compressor and remove as much of the mineral oil as you can than flush it with BVA100 ester glow oil which will mix with mineral oil if need be. I also had my old AC lines rebuilt at a AC shop and they put on all new barrier hoses. After you get everything bolted back up make sure you coat all the o-rings with ester glow oil before reassembly. Now go bring the car to a competent AC shop and have them evacuate them system than re-charge with R134a (use 75-80% capacity of the R12). Hope this helps. My dads 85S blow pretty cold on 85 degree days. The car keeps you very comfortable. It beats paying $35lb for R12!!

Mine was R12 when i got it and the system never worked at the time I got it. I got a good compressor from Neil (fellow Pelican here in Sunny San Diego), replaced all the o-rings (got from 928 Intl), new Drier from eBay and new Expansion Valve. My first attempt to do it myself failed which blew my original compressor up, so I eneded up taking it to a local A/C Shop which I referred to since he has done 928's in the past.

To sum the story up, I got's the chilly willy A/C now. Leave the Evac and Fill to the Pros. Period.

Here's my thread on the A/C
http://forums.pelicanparts.com/porsche-928-technical-forum/498002-c-compressor-drier-r-r.html

I got a vacuum pump and manifold gauge set from harbor freight.
I purchased 6 cans of Freeze 12 from carquest (14bucks a can)
I vacuumed down my system (late at night when the air was cool and humidity was low).
System held vacuum for 1 hour. (closed off the valve to see if it would lose vacuum)
Since this was a sign that I did not have leaks, I added 2.5 cans of Freeze 12.
After that (rear ac was cold but front was not) I replaced several vacuum lines that closed my Heater control valve.

My AC is now cold.

My cost for the tools from harbor freight was 60 bucks. Manifold gauges required some generic orings so the refrigerant would not leak.

ALl in all I suggest if you can get the 10 dollar air compressor actuated vacuum pump and test your system before you decide to convert. I think if you convert and do not replace all the parts the AC will not work and your compressor if the wrong oil is used will lock up .

dcrasta,

How did you get the air out of the line each time you connected another can of freon?

I'm with danno is just easier to leave this to the pros. Last time we had this done I think to evacuate and re-charge was less than $80 bux.

With the Manifold gauges you connect-
Blue line to low pressure (line that goes to the compressor under the radiator hose near the Aux-Battery Post)
REd line to High pressure (Fitting on the front near the 'sight glass' window
Yellow line goes to the Vacuum pump.

With the car off you turn on your vacuum pump, open the manifold valve on the blue line. The gauge should show you the vacuum on the low pressure side. After you get it to full vacuum, let the pump run for 20 minutes or so, then close the valve. I let the valve sit closed for 1 hour to double check I was not leaking.


Then you connect the 'freeze 12' valve to the bottle. The adapter should have a fitting that screws onto the bottle and a connection for the yellow hose. My cheapie hoses needed an extra oring between the yellow hose and the adapter that screws on the Freeze 12 bottle.

once its all connected (And all valves are closed) Open the valve for the freeze 12 bottle. The gauge set has a schraeder valve you can use to purge all the 'air' from the lines (With the freeze 12 bottle valve open enough to purge the line.)

After you purge the lines, start the car, turn on the AC on full cold, (Both if you have a rear ac). open the valve on the freeze 12 bottle completely (yoru gauges should still show vacuum) then open the valve to the low pressue (blue) hose side. You should go from reading vacuum to reading positive pressure. Once your bottle is empty, close the blue(low pressure side). You should show a few PSI (10-20 psi). Add a second bottle until your reading on the low pressure side is 30-50Psi (I added until I was about 50psi on the low pressure side). High pressure should read ~ 200. AC should be cold.

http://ecx.images-amazon.com/images/...EL._SS500_.jpg this is what the gauges look like.

Oh that makes sense so you can purge the line.

Did you check the pressures at 1500rpms? I was told by other porsche mechanics that the AC pressures are checked when the car is at 1500rpms.

Dcrasta, I like your suggestion of the freeze 12, I didn't know there was a replacement. so are the original oil in the lines and compressor compatable with this stuff. If that is the case I will just replace the o-rings and give it a try. Which vacume pump did you get from Harbor frieght? Thx everyone for the feedback will way the options a little more.

R12 isn't that hard to get, ebay and other sources have the cans, and our systems are designed for R12. R134 is higher pressure and less cooling capacity. Mine is now R134, working fine, but not ice cold. Doing it again I would leave it R12.

Running the vacuum pump, which you should do for at least an hour, does two things, pull all the moisture out of the system, and the check for leaks, but leaks might also on show up under pressure.

BTW Big Lots has R134 cans on sale again for $5 each.

*************** Story with wry humor below.
I bought a couple of the $5 cans and the HF gauge set months ago, to be ready for problems. Wife's car stops blowing cold, and I think great time to show my skills. I couldn't find the blinking gauge set in my garage. Apparently I buried it when I brought home a dozen subwoofer boxes I got a deal on, so I end up on a Sunday afternoon at Autozone buying an adapter for $25 that is nothing but a valve that pierces the seal on the cans. $4 freaking dollars less than what I paid for my HF gauge set for this knob with a pointed thing. Didn't fix the car either, ended up in the shop for a new compressor etc.

A dozen subwoofer boxes? No wonder you don't have a garage to buy another 928.

I have an additional question. I'm in the process of trying to make the a/c system working, I have determined that there are no vacume leaks and all the airvalves are working and directing the air as there suppose to. The one problem I'm having is the heater valve, the one located at the fire wall is staying opened. I realize that this is the normal position for the valve and that it is closed via vacume. My question is the only time that is closes is when the bottom slider is set to the off position. In all other positions the valve losses vacume and opens. Even when I have it set on Auto and the temp set to 65. Any one have some experience with this I fig that in auto and the temp set to the lowest setting the valve should be in the closed position to have max cooling.

Por917,
You can convert to R134a and have a cold car, I've run three different 928's I've owned over the years and never had a problem..... provided your compressor and hose lines are in good shape.
Otherwise you need to follow certain procedures in the conversion process as well as evacuation, charge and test.
As far a 'new' compressor's crashing, its not the 'new' compressor but rather a system problem such as poor oil flow.

PM if you need help.

I used the cheapest vacuum pump (8 bucks with coupon) which was able to draw down to 30hg of merc vacuum.

I left it running for 1 hour.

I turned the car on after hooking up the freeze 12, ran the freeze 12 in.

Checking the High pressure side at 1500 rpms, 150psi. (within spec). May need to add a little to get the pressures up to 200 psi, but its working fine.

Oh and I ziptied my heater control valve shut . I also need to replace/troubleshoot the vacuum manifold. But thats about it.

Ok understand how it works...

If you have 'ANY' vacuum leaks, once you shut the car off (and the vacuum source=engine so no more vacuum) the leaks allow the vacuum to 'relax' the heater control valve. Its default state is open.

Once you start the car, the leaky vacuum system takes a few seconds to restore the previous setting (closed). U get a blast of hot air.

Properly working Vacuum system maintains vacuum for some time after the car is shut of, keeping the heater control valve closed.

One trick is to remove the lower airbox lid, and then ziptie the control valve arm shut. This closes the control valve (remember to remove zip tie once weather changes).

You may also have a short in the HVAC control head (like I do.) . This also controls the outside/inside air mix. IF you have a short, it will allow outside air in, diluting the cold air.

I would zip tie the control valve shut, then trouble shoot the HVAC manifold using a mighty vac tool. (u should basically troubleshoot and replace all the vacuum hoses as it affects multiple systems like the Cruise control, Automatic transmission shifting, etc).

Once everything is working properly, you can remove the zip tie (or like I do, just leave it closed til the weather changes..)

Freeze 12 is chemically compatible with R12 and the OIl for R12 compressors. Its the cheapest way I know to recharge a r12 car.

If your compressor is working, and you pass the 'vacuum' test (holds vacuum for 1 hour or more after the vacuum pump is shut down), I would just go for the R12/Freeze12 refil.

If you compressor is damaged, or your system's integrity checks fail, you need to replace Orings (although if the integrity is good and compressor fails even when jumpered, maybe just the compressor replacement).

The problem with converting from 12 to 134 is the compressor oils are incompatible, and the receiver/drier also has left over refrigerant. U can google specifics, but to convert to 134 requires a different oring, different compressor oil, new receiver-drier, and evaporator has to be flushed also. Not 'EASY' but not 'difficult' (As this conversion does not require precision measurements or procedures that are 'hard').

I still haven't had the question about the heater valve operation, can anyone shed some light on this for me? The only time I'm getting vacume to the valve is when the lower slider is in the off position, which is OFF. All other selections the vacume is gone and the valve positions it self to open thus allowing hot coolant to the evaporator. I know that the valve is spring loaded to the open position. I just wanted to know if anyone knows what might be going on here. One more note. The valve will still stay open with the lower slider set to auto and the temp selected to the lowwest temp. Any info will be apperciated Thx.

por917 from the info provided you need to get under the dash on the driver side, look at the setting motor.
turn on the key with the lower slider moved to the off position,
move the top slider slowly from cold to hot see if the setting motor is is moving.
Also then move the lower slider to the first position. and move the temp slider again checking for motor movement
if not then there is probably a bad transistor they can be replaced there are 4 of them .
The setting motor has the signal for the solenoids going through it , if one of the transistors fail then the motor wont send the signal to the solenoids

The other thing to check is run a vacuum test on all of the individual pods,
if all of them are not leak free than this can also cause the valve to not shut.
also make sure the reservoir tank and CC lines are also holding vacuum

Most of your answers can be found here:

Porsche 928 Maintenance Tips and Procedures

Thx Mr Merlin, I will look into that this weekend, I'm pretty sure the vacume is all okay did the tests with the mity vac last weekend all checked out. you answered what I needed to know. which is what signals would energize the vacume relay for the heater valve. Thx and to all the others with trying to answer my questions about climate control Thx too, I think I'm going to pass on converting to 134a and just go the route of freeze 12. This sounds like a much better solution to converting the system.

Mr Merlin, one other question? Are these transistors located in the control module or in the setting motor?

the transistors are in the setting motor remove the lower parcel tray ans then 2 screws and it will pull out snap the arm out with a screwdriver i will look for the transistors #s

AC problems

http://forums.rennlist.com/rennforums/928-forum/567743-hvac-now-working.html?highlight=setting+motor+

Living in Florida you really do need the HVAC to work. My 928 was converted to R-134a before I bought it and the a/c seemed to be working, the compressor was engaged when the a/c button was pressed but all I got inside the car was hot air so I decided to investigate, I did a search and read all the posts on a/c I could find and with Dwayne’s write up, Wally’s paper and John’s site, I set to.

I found that all the vacuum actuators held vacuum which was a relief, the sensor chain was working correctly but the setting motor arm wasn’t moving, testing the vacuum solenoids revealed two not holding vacuum, the white line going to the heater valve and the blue line going to the fresh air/inside air flap.

I bought some used solenoids and a setting motor from Gio and replaced the leaking solenoids but the setting motor was like mine, broken, I had seen a post awhile back about replacing the transistors in a setting motor so I removed the circuit board and replaced the transistors with some new ones, when refitted and the temperature slider move from one end to the other I could now hear it moving the flaps.

One other job was to check the front of the evaporator for clogged fins and debris, I removed the rubber bellows between the blower and heater box, this is just enough to get an eyeball of the front of the evaporator, mine was clear. If it was dirty you would need to remove the blower to have enough room to get a brush and vac in there to clean it.

On testing on the road I now have cold A/C and controllable, the temperature at the center vent went down to 30f, outside temperature was 88f. When the system works it works well.
After all this I understand the 928’s a little better but without the help of those mentioned above and all of the other posts I’d still be in the dark or should that be sweating profusely.
Picture of transistors I replaced (2 x BC 327, 2 x BC 337)

Thx kuehl a good source.

Mr Merlin, I think you might have something there, I didn't get any movement from the control unit while moving the slide switches, you where refering to the unit on the drivers side next to the center vent actuator correct. This is the unit with 2 electrical plugs .

I agree with the learning aspect of this everyday I get a better understanding on how this car works and get a little bit better on troubleshooting. It can be painful at times though :)

the AC problems has a picture of the setting motor under the pod

Thx MrMerlin, that is what I thought, do you have any of those transistors handy :)

take the motor out take it to radio shack and see if they can match them up the previous post that linked to Rlist has the numbers and a picture of the parts in question.
you may have to join up there if you have not done so to read the post and see the pictures

Yes I have been there and got the numbers and pic, thx I will try that this weekend. I will keep you posted on the progress.

you may also have to order these online or buy them from the OP that fixed his

Another check I read was if the rear AC (if you have it) is cold but the front vents hot then the problem is not the refrigerant level but the HVAC controls or the Motor or vacuum signal to the heater valve.

Best of luck man 'Porsches are not cool with no ac.'

Just a follow up on the HVAC system, I did further troubleshooting and discovered that the outside Temp sensor is the failure in the system. Once I took the sensor out of the loop the heater valve and setting motor functioned normally. The Temp sensor failed by showing infinite resistance.

check the connector pins they can corrode where they are soldered onto the wires

Yeah I checked that I ended striping the wires 3" past the connector and still infinite resistance which equals bad sensor. So it looks like I'm buying a new one ouch 100 bucks for a used one. over 200 for new. But at least I know what is going on now.