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.