Broken A/C troubleshooting

[BennSport]

Hey guys, I’ve been trying to figure out what’s wrong with the ac in my early 944 and I’d like some help. My first thought was that I had ran out of r12, so I went and checked that. When I press the schrader valve on the high pressure side some gas shoots out so I can only assume that. I did also notice that the line for the vacuum unit (944 573 053 00, #39 in diagram) has snapped off so i wondered if that was the case as well. I moved the plunger to see if that would do anything but it made no difference. Where would you guys start looking next if you were me?

[c5_pilot]

That just controls a vent door. Check all the hoses, compressor and condenser lines for any oil or dirt covered oil, which would indicate a leak. The evaporator is harder to check as it’s behind your glove box and requires dropping down to investigate. Mine was leaking from the shaft seal on the nose with the compressor behind the clutch pulley. It was obvious from all the oil and dirt. If all that seems fine it could be your low pressure cut off Switch kicked in because you’re low on refrigerant. You can test test this with an ohm meter. You can also jumper the compressor to see if the clutch kicks in bypassing the low pressure switch. Only to do this for a few seconds, however.

[Tom]

You can also jumper the compressor to see if the clutch kicks in bypassing the low pressure switch. Only to do this for a few seconds, however.

That was my first thought too. Also, look to see if the compressor clutch is engaging. If not, maybe put a set of gauges on it to see what's really in there. I wouldn't rule out low refrigerant just because it hissed -- it will make a good hiss well below the pressure needed to kick on the compressor.

[BennSport]

Okay I’ll check to see if the compressor clutch engages today. If I end up jumping the low pressure switch how long can I leave it on for safely to see if the air starts blowing cold?

[Tom]

If it's not kicking on, I'd go to O'Reilly's or other auto parts place where you can rent a gauge set. I wouldn't jump the compressor or low-pressure switch and let it run for any length of time. Probably safe to jump the compressor momentarily to see if the clutch works. And then separately jump the pressure switch to see if that's what's preventing the clutch from kicking on. It's probably low on r12, possibly among other issues. Finding more r12 might be the biggest challenge, so it might also be time to think about converting to r134a. These systems do pretty well on r134a actually.

[BennSport]

Do those guage sets work with the r12 schrader valves? I was considering an r134 conversion but i figured it would be easier for me to top off since I already have r12 still in the system. I’d rather not deal with the price of having a shop evacuate r12 since it’s quite pricey. I found some r12 kits for a reasonable price, but I have 2 concerns. The first being I wouldn’t know how many ounces worth of r12 to add since the system isn’t fully empty, and that the kits only have 1 gauge to measure low side pressure so I wouldn’t be able to check high side pressure. At least I wouldn’t be able to check it at the same time

[Tom]

You can get cheap gauges that do r12 and r134a, such as:

https://www.amazon.com/R134a-Manifold-C ... 9258&psc=1

Have you looked around for r12? It's not easy to come by anymore, and the NOS cans on eBay are silly expensive:

https://www.ebay.com/itm/326635367219?_ ... R5r4ldTuZQ

Not to be 'that guy" but I've found with A/C, it's hard to get good results without pretty much doing it 'by the book' -- i.e., evacuating, pulling hard vacuum, checking/fixing leaks, changing the receiver dryer, new refrigerant with a gauge set. If r12 were $10 a can, like the good old days, it might be worth 'topping it off' to see if the system wakes up, but if the system hasn't worked for a while, just topping it off is probably going to be an expensive disappointment.

When was the last time the system worked and cooled well?

[BennSport]

Okay that’s good information, thank you Tom. I think I’ll proceed with the conversion then. Do I need a r134 compatible dryer? Because I haven’t found much information regarding that. I’ve researched everything else, including a 90 degree compressor fitting and the different charge capacity. I’ve owned the car for over a year now and the ac has never worked.

[Gaspowered]

Our host (@Tom) has a pretty good thread on what he did to the a/c on his 944 turbo.

viewtopic.php?t=425

If you're planning on keeping your current compressor, I'd remove it and drain all the oil out, clean it and put in a pag or esther oil.
I would also get a conversion kit, new barrier hose and new drier.

Here are a couple dependable of sources;

https://944online.com/

https://griffiths.com/


Here's a good video to watch as well.



Cheers

[BennSport]

So I just checked the car and the a/c clutch does in fact engage when I turn the ac on in the cabin. What would my next step be in diagnosing this issue?