My First Adventure in A/C...
 

...was a wash - at least so far.

First up, we did Trav's 86 951.

We replaced the drier and it's o-rings, then drew the system down to a heavy vacuum --- -30 inHg and left it there for a half hour. We did this again when we found one of the hoses wasn't secure (the vacuum wouldn't hold), and the second time it held for 10 minutes after turning the vacuum pump off.

With the engine off, we added most of a can of refrigerant (Duracool), then, with the high side valve turned off and the low side valve still on, we started the car and turned on the A/C.

Nothing!

So we jumped the pressure switch. The compressor clutch did engage, but it doesn't appear to do anything. If you turn off the flow of refrigerant and open the high side valve, both high and low side pressure values are the same - around 65 PSI.

Is the compressor shot?

A second question: The pressure cut-off switch is the bottom switch in the well by the driver's side headlight (two leads with spade connectors) but what is the other switch above it, next to the drier? The refrigerant temperature switch? We couldn't disconnect it.

http://www.mikepellegrini.com/Graphics/IMG_1794.JPG

It sounds to me like you need a new compressor.

"The compressor clutch did engage, but it doesn't appear to do anything."

If the compressor clutched engaged, and the compressor's outer hub was turning,
with your service gauges set to read the system pressures (both gauges closed), are you saying you did note a pressure difference? Or are you saying with the engine off you noted equal system pressure on both sides?

I believe on some model years the low pressure switch and high pressure switch are seperate switches, where as on my 89 they are combined into one switch.

AJ

" A second question" answer...........

http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/675288-technical-bulletins-anyone-have-access-them.html

John

Also

If it turns out to be your compressor and you don't want to go with an OEM reconditioned unit or rebuild you own, I recommend a new compressor form Kuehl. I went that route about 5years ago and it has performed very well for me. Just my $.02

A.J.

Okay. Hey thanks John for the TSB.

Okay. With the compressor not turning, pressure registers about 75 PSI on both sides. When you jump the pressure switch, the high side dips to about 25 PSI and the low side starts climbing - eventually maxing the gauge.

That's with one can of Duracool. A full charge according to their conversion sheets is two cans. I didn't add any oil because I'm assuming the system still has its original oil, and the ester oil from R-12 is compatible with Duracool.

reverse the hoses you have them on backwards
blue suction
red hi pressure

That's what I was thinking, but the Schrader valves are different sizes so in theory, it should be impossible. The red hose is a fair bit larger connector.

Okay, so I was hooked up backwards.

I swapped the lines and suddenly, the numbers make sense. I put two cans of refrigerant and one can of oil in my 951, and it's cooling great - at fan setting 3, vent temps are in the low 30's with an ambient temp of about 65F.

High side pressure averages about 80, low side between 15 and about 40 - average about 30.

But the R-12 ~ R-134a conversion fittings I got are clearly wrong - at least for our cars.

http://www.mikepellegrini.com/Graphics/IMG_1796.JPG

You can't really see it because of the flash, but the smaller, blue fitting has a nice "L" stamped in the top of the cap. The fittings are different diameters so you can't mix them up - the red fitting is a fair bit larger than the blue fitting (it's a light blue, difficult to see with the flash). And they mate perfectly to the red and blue R-134a hose set I bought.

Oh well. I'm happy it works.

So what about my son's 951? There an obstruction in the system or something?

Once again, his car's symptoms are this:

Okay. With the compressor not turning, pressure registers about 75 PSI on both sides. When you jump the pressure switch, the low side dips to about 25 PSI and the high side starts climbing - eventually maxing the gauge.

That's with one can of Duracool. A full charge according to their conversion sheets is two cans. I didn't add any oil because I'm assuming the system still has its original oil, and the ester oil from R-12 is compatible with Duracool.

The vent still blows room temp.

Good deal
High side pressure averages about 80, low side between 15 and about 40 - average about 30
damm that's some good no.s for that temp.
your other prob i would think a blockage. try again. the pressure line should heat up some till the blockage and cold after to locate. dont let your pressures get out of hand... pressure up then shut off and run a temp scan.
good luck

Thanks, we'll give that a try.

We did my son's second car, an 88 NA today and it went just fine. We'll get his 951 back maybe tomorrow and see if we can figure out what's blocked.

And yeah, I noticed the R-12 schrader valve fittings are the SAME size. Both R-12 hoses fit on either side. So I assumed the larger, high side R-134a conversion fitting would go on the larger line... D'oh!

I'm a moron...a moron...a moron...a moron... a moron...a moron...

Are you trying to using Duracool with R134a charge port adapters?

Yes. Which as it turnsd out was un-necessary because I ended up with a set of R-12 hoses. Oh well...

Did you put some form of refrigerant conversion sticker or warning label visible in the engine compartment, like next to the service ports, so that someone is aware of the type of refrigerant you have in the car?

This is done for 2 reasons:

1) If someone other than you, such as a new owner of the car or a technician, services the AC they will know that:
A) Since you have R12 service ports they would expect the system contains R12. Different refrigerants produce different pressures and operating characteristics.
B) They don't try to add R12 to system that is not R12

2) If a service center recovers the refrigerant in their R12 machine they won't contaminate their recovery/recycle bottle with an unknown refrigerant that could be end up in another vehicle.

Not currently but then I'm the only person that works on it. If I ever sold it (which is unlikely) then I would. I am aware of the reasons you cited in the modified version of your post. I do want to be responsible.

Duracool's cheap. I'm thinking next summer, I'll drain the refrigerant off and take the conversion fittings off, then recharge it with the R-12 hoses, like it s'posed to be.

I don't like doing things half-assed or badly, but when you're learning new disciplines, sometimes that's what happens.

I always wanted to learn how to build computers, and eventually did. But you should see how many computers I destroyed getting there. This is kinda the same.

There's always a learning curve, and right now I'm at the start with A/C...

Okay, I looked and they sent me a bunch of stickers with the refrigerant. How about this:

http://www.mikepellegrini.com/Graphics/IMG_1800.JPG

We've still gotta figure out what's wrong with my son's 951. He's bringing it over later...

Much better!
A sticker makes one aware of what stuff is in there.
Legal. No. Ethical. Yes.

I can remove the adaptors on my car w/o letting out the refrigerant.