rastapapa

We have an automatic '82 928S that was converted to R-134A before we bought it. It has never blown cool air for us and our mechanic said that he got the compressor clutch working and that it probably just needs a freon recharge.

I was poking around jc whitney and found this:
http://www.jcwhitney.com/arctic-free...2y1982f6z160j1

theres one review which sounds positive but it says something about a low pressure connector which Im not sure if thats on the 928 end or this can of refrigerant's end.

Just wanted your guy's thoughts and to hear any experience with recharging one's refrigerant. Do you know generally how much it costs to get an empty system recharged professionally?

Thanks!

BTW we are in los angeles and planning our wedding in palm springs. Thats why Im asking about a/c now.

SQLGuy

I'd call around and find a shop that will cut you a reasonable price for a proper service and charge. Since it's never worked for you, you don't know whether there are small or big leaks, whether there's oil in it, etc. Being the off season, you may be able to get a better price, or at least more flexible appointment times.

A shop will have the equipment to pull a strong vacuum on the system. This will ensure that any moisture and air is removed before 134a is added. They'll also check to make sure it holds vacuum... if there are larger leaks in the system, the vacuum test will identify them, so you're not wasting refrigerant in a system that can't hold it. If it passes the vacuum test, they'll charge it and can then verify that high and low side pressures are reasonable - which will be some indication of the health of the compressor and that the expansion valve(s) (1 or 2 depending on whether there's rear A/C) are not blocked. Generally they'll also add leak detection dye, and include in the service cost a follow up check so that if there are more minor leaks in the system, they'll be able to see where they are.

If you were more sure that there were no major leaks, you could save a bit of money by first charging the system, and then having a shop do an evac and recharge. That way they wouldn't be selling you refrigerant, but a lot of shops are pretty reasonable on their 134a prices, and the evaluation on an unknown system would be worth it to me, anyway.

nuc

Your mech. must have jumpered the compressor. Your system has a low pressure switch and if the system pressure is below that, the comp. won't kick on.

If you are low or out of r134a, you have a leak. Refrigerant does not get used up, it leaks out

If your system is not holding a vacuum, that can will have a hard time even going in. If you do get some in your system will still not work because it will be full of non-compressibles. To get refrigerant into a system, first you need to pull a vacuum. The quick and dirty way, if you have access to a two-stage pump that can pull a deep vacuum is, pull a vacuum and fill to correct pressure. Or fill until your hands feel cold air coming out of the vents

Don't worry about dryers or nitrogen purges, etc.... Hopefully the leak is slow enough to get you through your trip, before all the refridgerant leaks out.

When you get home, have someone with a halogenated leak detector go over your system. Then change out the dryer, etc....

Welcome to the world of leaking o-rings, expansion valves, refrigerant lines made for r12 and more

rgs944

If it is low on freon that means it has a leak somewhere. If you fill it that could mean it could leak out in 2 minutes or 2 months or 2 years. If you are lucky it might be a slow leak to get you through your trip or it could last a lot longer. If it was me I would buy the can of recharge and try to fill it and see what it does. As long as you understand exactly which port to use so you do not get hurt you will only be out about $30. The compressor might not come on if it is too low. What you can do is turn the AC system on high with the car running, then connect your recharge can to the low pressure port. Then get a bucket of very hot water and put the freon can into the water as you trigger it in. The heat from the water will move the freon into the AC system. If all componants are working as they should the compressor should soon kick on. Use the gauge on the can to see where the level is at and where to stop. This is the easy way to do it but not the right way. The right way takes lots and lots of money.

rgs944

Does 134 put more pressure on the seals than r12? I read that somewhere but do not know if it is true.

nuc

pressures are ~10% higher for 134a compared to 12. No problem for the o-rings/seals. The problem is the hoses for an r12 system are not barrier hoses as are needed for an r134a system. Also, to take full advantage of the 134a a parallel/multiflow condenser could be used which have more flow capacity.

For the cost of buying r12 off ebay, there really isn't a reason to convert unless you already need to change all the hoses anyway.

Speedtoys

Ok..can you convert -back- to R12??

nuc

Sure, but then you have to undo everything that was done in the original conversion. Drain compressor and flush entire sytem of PAG oil. Change dryer and fill compressor with mineral oil, and then remove the converted fill ports that were red lock-tited on, fun!!

Then do your normal evac and charge.

Speedtoys

Great...I really think Id like to follow this method..I like ice cube A/C..and I have an issue with the system _anyhow_..so I wouldnt mind R&Ring it..


I read that flushing the system is with the compressor off..what does that?

blown 87

Just flush the system and charge with oil and fill with R12 after taking the charging adaptors off, I have never seen a drier, hose, or a seal that was for 134A only.
sounds simple, but the reality of it is a bit harder as the system will need to be taken apart to do a flush correctly.


Pressures of 134A can be whole lot higher than ten percent, I have seen high side pressures of conversions approach 500 PSI, and that is hard on compressors, lines, everything on the high side.

nuc

R-12 refrigerant as a liquid, would have about 117 PSI at 100 degrees F. The pressure reading of R-134a at that same temperature would be about 124 PSI. For this simple fact, R134a gauge readings will be a little different as compared to R12. Should be around 10%.

Pressures up to 500psi sounds like there was some refrigerant mixing! Maybe even putting some r22 in there (you know, hey, I just had a big green can of "freon" laying around, and I know it works good in my house!) J/K, don't do that!


Straight R-22 can cause extremely high discharge pressure readings (up to 400 or 500 psi!) when underhood temperatures are high. That's not just hard on compressors, that's compressor failure

[QUOTE]Nothing is r134a specific, however, if you want a truly leak free system with 134a you need barrier hose, as the 134a molecule is smaller then r12 and will migrate over time through hose designed for r12.

Everything "sounds" simple with the 928, right?

blown 87

Have you ever touched a condenser when a AC was running?
Gonna be a damn sight more than a 100 degrees.
I have seen factory systems that have never been touched get high enough in the Georgia sun to pop the pressure valve.

117 psi is funny, even a normal r12 system will run close to 200 here on a hot day, you let a 134A system with no shut off get in traffic on a 100 degree day and it is going to go very high..
You are trying to compare static liquid pressures with what I said running high side pressures were.

SteveG

I had to do some research and it's still not clear, which is all the more reason I suggest you don't use the term Freon (EI Dupont's trade name) for refrigerant b/c it can confuse R12 and R134a. Especially in a case when there is talk of going back to r12.

I think your first question was cost. I had a system (not 928) checked for leaks and re-charged with 134 two years ago and it was $300, no parts. We knew it was a switch in dash, but this shop insists on complete drain to cover their rear w/any type of guarantee. WAG is $600 to $700 depending on parts, but could go much higher.

You have a difficult situation b/c the decision is whether to follow it piece meal and hope you only need to replace one hose or say the drier or end up replacing everything, which might be cheaper in the long run, if you did it at the outset. Do you know exactly what was done or added when it was converted? Good luck.

dprantl

It is true that dynamic high-side pressures will get much higher than static tables. 250-300psi is not uncommon. However, I can't believe that 500psi didn't blow something up

Dan
'91 928GT S/C 475hp/460lb.ft

blown 87

I said near 500, and I have seen them blow up, will make you jump when it lets go.

In a well running system on most cars that were designed for R12 and have been properly converted to 134, temps in the 90's with only the airflow generated by the fan, most will see around 300 or so on the high side, depends on the amount charged and a lot of other factors.

R12 in the same system will be around 200-225, depending on the same factors.