What To Do Next? R134 or R12

[nmwhitneyjr]

This is a different take on the usual "which refrigerant" question. Let me explain:

I have a '79 Porsche 924 I bought about 8 months ago. PO told me the ac didn't work. There's no r134 conversion sticker and I have several cans of r-12 in hand (from a prior project). So yesterday I decided I was going to vacuum the system down and if it held vacuum, charge it up. Well, I located the ports and there are r-134 fittings installed. I double checked for a conversion sticker... found none.

The car was rescued out of storage about 3 years ago by the PO (out of CA). It had been sitting for about 20 years. PO spent many thousands on the car to get it road worthy. No work was done on the AC at that time. There are no maintenance records for the vehicle prior to the PO's purchase.

There was almost zero pressure in the system when I hooked up the gauges (which I suspected). The system barely went pfft when I opened the low side. No pfft at all on the high. So I vac'd the system down for 3 hours, then closed off the pump side of the gauges. I did not expect it to hold vacuum. 12 hours later it's still holding at -29.5.

Now I'm unsure what to do next. I don't want to open a system that is holding vacuum. If the car had a proper r134 conversion (where I'd expect to find a sticker) I need to put r134 back in, right? But I suspect that someone in the distant past slapped a set of r134 fittings on it, vented it to atmosphere, and just dumped r134 in the system (without concern for oil compatibility, replacing the drier, etc) and called it "good enough." Then the car went into long term storage and the r134 leaked out via the original, "non barrier" hoses. The drier is original (or at least it has a sight glass). The condenser is the standard tube-and-fin design.

What do you folks advise?

[tbirdtbird]

In a case like this all bets are off when it comes to the condition of the components. We worked like crazy on the same model and ended up finding that the front evap was totally clogged with hair, dirt, leaves, etc. getting to it for service was a nightmare of course.
Often when a 134 conversion is done by a DIY the sticker never goes on. Be sure the shraders on the R12 fittings have been removed unless the adapters have depression pins.
You are correct in assuming the hoses are not good.
I would disassemble everything I could to replace hoses.
The condenser with that design can be flushed.
When you do so, carefully collect and examine the used flush for any type of metal fragments. If this is what you find then the comp has grenaded. In that case the condition of the expansion device is in question.
The hoses going to and from the evap s/b replaced, despite that the access will be difficult. At that time the evap can also be flushed.
The f/d needs replacing. The O-rings need to be the new green ones.
I would use blue nylog on all the orings. You can get it on-line. Parts stores will not have it.
If you need new components then consider getting them from www.ackits.com . The board owner and site owner, Tim, is a very good source of parts. His prices and quality cannot be beat. He has been doing this for years. You can also get a good quality flush from him. The flush you get from the parts stores is of a very low quality and is difficult to dry out.
You seem to have enough knowledge to make all this happen, it is like starting all over. But as you seem to understand that is better than patching a system.

[JohnHere]

Been thinking about your post since you wrote in this morning.

As tbirdtbird said, you can flush both the evaporator and condenser due to their designs. But as he also astutely pointed out, you don't know whether the exterior of the evaporator is plugged with debris without removing it. I also agree with the remainder of his assessment, including the hoses.

Your evaluation is also valid. If long ago someone just dumped the R-12, added R-134a, and didn't do anything about thoroughly flushing-out the old mineral oil, you definitely have problems.

To be on the safe side, and to avoid having to do the job all over again, I would keep it R-134a, holding onto your R-12 (or sell it), and replace everything with new components. In so doing, you could swap the existing condenser with a more efficient parallel-flow type. If finding barrier hoses is a problem, have new hoses custom made by a specialty supplier, such as Cold Hose in Florida. I would expect everything else to be available from Tim at ACKits.com

[Windery]

Since it's holding vacuum well, you might want to stick with R12 if that's what was originally in there. It’s likely to be more compatible with the old system components, especially since the dryer and hoses are original.

[JohnHere]

There was almost zero pressure in the system when I hooked up the gauges (which I suspected). The system barely went pfft when I opened the low side. No pfft at all on the high. So I vac'd the system down for 3 hours, then closed off the pump side of the gauges. I did not expect it to hold vacuum. 12 hours later it's still holding at -29.5.

You should note that a system holding a vacuum for hours doesn't necessarily mean that it won't leak while running under the positive pressure of a full charge, particularly on the high side.

[tbirdtbird]

Not sure I would put much faith in the comment from 8:12 am

[nmwhitneyjr]

I found the contact info for the PO I purchased the car from and called him. The estate he bought the car from didn't have any records about the a/c conversion to r-134. But when he had the refurb work done (by a porsche specialist) to get the car driveable, the system was recharged with r-134 and worked fine for about 2 years. He was living in NV at the time. After he moved to the East Coast, he didn't drive it daily and it slowly stopped cooling. It never grenaded or had any other mechanical issues under his ownership.

With that information, would it be worth a try to fill with r-134? I know that it's going to need hoses, all new o rings and a drier. But I'm primarily keen to see if the compressor works and get some uv dye into it to see if any leaks develop in other components (condenser and evap specifically). I don't want to spend the money/time on hoses, drier, etc to find the system leaking like a sieve elsewhere.

[JohnHere]

With that information, would it be worth a try to fill with r-134? I know that it's going to need hoses, all new o rings and a drier. But I'm primarily keen to see if the compressor works and get some uv dye into it to see if any leaks develop in other components (condenser and evap specifically). I don't want to spend the money/time on hoses, drier, etc to find the system leaking like a sieve elsewhere.

You could try evacuating and recharging it. However, some significant if's, and's, or but's remain.

For example, we still don't know about the mineral oil and whether it was thoroughly flushed from the system before PAG or POE oil was added; the integrity of the compressor (original, leaky shaft seal, leaky case, clutch, etc.); whether the R/D is original or replaced with one having R-134a compatible desiccant; any additives in the system (sealer); and so on.

All told, I'm unsure what you'll gain if you recharge it now, add UV dye, and then find out about all the system's deficiencies later. The system might run for a while, then fail again.

If the car was mine and I planned to keep it indefinitely, I would spend the money now, start from scratch with a "dry" system by replacing every major component, including the hoses, o-rings and seals, with new parts. I would also use a "sniffer" to leak-test instead of adding UV dye.

[TheBandit]

That is an interesting dilemma!

I'm not familiar with the 924 - what kind of system is it? TXV? What does it do for low side regulation? Clutch cycling?

On my old GM POA system, I know it's important to adjust the POA valve so the evaporator will run at appropriate temperatures when converted to R134a. I understand it's also important to use a parallel flow condenser because the old tube and fin condensers aren't as good at rejecting heat and become a limiting factor with R134a. If your system has similar limitations R134a may not work so well without making changes BUT it sounds like the previous owner had good luck with it until it gradually stopped working. The gradually stopped working part makes me think the system leaked down and lost charge, so at a minimum I would perform a pressurized (not vacuum) test of the system and try to locate the leak. I would also make sure that you hear flow into the evaporator when you supply pressure to the high side, confirming the TXV isn't gummed up. If the system is still using hose-clamp lines and non barrier hose, perhaps that's why the R134a leaked over time and you might get away with just swapping the hoses & o rings before recharging. You probably should consider a new F/D and add a hi/lo safety switch if it doesn't have one.

If this is your car and you are planning to keep it, you might want to dive in deeper. Curious to hear what you end up doing!

[GearVirtuoso]

Hey there, it sounds like you've done a good job diagnosing the situation with your Porsche's AC system. Since the system is holding vacuum, that's a positive sign. Given the uncertainty of the refrigerant type and potentially improper conversion from R12 to R134a in the past, I'd recommend starting fresh. Properly evacuate the system, replace the drier, and ensure all components are compatible with R134a. It's always better to err on the side of caution to avoid potential issues down the road. Have you considered reaching out to a local mechanic or AC specialist for their opinion on the best course of action for your specific situation?