Quick background...

Bought car in the winter, a/c didn't work, PO converted to R134, didn't care then, it's about to get VERY hot in AZ, I care now, trying to fix, read below...

No pressure on the low side, I hook up venturi style vacuum pump and manifold to see if there is a leak before I attempt to start replacing everything. My air compressor is kind of lame and I can only get about 19" vacuum on the system however it has been holding that for 4 hours now without a loss. Am I safe in assuming that I don't have a leak? I know you need to pull 29" for hours in order to boil off the water before refilling, but at this point I'm just checking the mechanics.

I also know I'll need to get a new dryer and might as well replace the expansion valve but I'd like to not have to replace the compressor or track down mystery leaks once I do recharge.

It depends on the compressor. The front seal likes to leak, especially on the R-4 design.

Look for oil/dirt residue on all the connections. I ended up buying a new compressor last year. The rebuilt just lasted a week past it's one year warranty. Get a Hodyon (Hancock Industries) compressor. If you are going w/R134 again, get the thick GM specified oil or BG Fridgiquiet.

Holding vacuum is different than holding pressure, so no guarantees. Plus you need to use a good pump to get to 29" IIRC, anything less then 24" does not extract all the moisture.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Well, I don't have any experience with my Mercedes...but with my Toyota, I know that it would only pull about 24" vac...I refilled with R-134, and it lasts about a year and a half before I notice that its not working quite as well as it should and it needs a recharge...

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

On the subject of background, what is the year/model of the car in question?

No. The typical operating pressure exceeds that pressure differential by a factor of 30.

Need more info. If PO had converted, how long ago and did the items listed above get replaced then? Trying to figure out why you assume the drier and expansion valve need to be replaced. Is there any pressure on high side? Is there any refrig in system currently? Have you tried to fill system if the above answers are no? You can purchase or rent a leak detector real cheap, fill the system and check for leaks. Lots of options before just tearing into system and replacing parts just because you think they are bad.

Also FWIW I have done countless A/C systems and have never pulled more than 19 - 21in vac on any system including my own 134A conversion 7 years ago and blow low 30's out of vents in mid summer.

Only what was left after pulling 19" of vacuum!!!!!!!

Even a moisture-laden system can work for a while.

Sorry... 82 300D, I don't know when the parts were converted and there is 0 pressure on the low side or high side. So I do need a new dryer no matter what as i'm sure it's saturated by now. I've got so much grime on my compressor from my leaky oil cooler lines I can't tell if it's got that tell tale oil "dusting" around the seals. So how's the luck with the rebuilt R4 compressors? Worth a try or do they always take a dump in short time?

It has been my experience that the older R4 compressors work fine on R12 or ES 12, but the higher pressures associated with R134 will shorten it's life somewhat! I did a successful conversion, but I went with Envirosafe Refrigerant and it makes a world of difference! Envirosafe is not poisonous like R134 and it requires a lot less of it and it works best next to R12. It also operates at much lower pressures and it is compatible with all compressor oils, but oil for an R12 system is still easy to get and works better. I live here in Apache Junction AZ and i drive in the summer with no problems. Envirosafe or ES 12 because it does operate at much lower pressures, your fuel economy improves dramatically and your acceleration improves greatly with the system at maximum too! I'll find the link to envirosafe and post it here in a minute or two. It has to be odered over the internet, it's not available locally, but it is worth it since we have a little time before the heat get's fierce!

http://www.es-refrigerants.com
http://www.duracool.com

Duracool is another hydrocarbon based non-toxic refrigerant that works well in these systems too and there are dealers close to Arizona as well. Envirosafe will arrive quickly with a credit card and it is also a little cheaper by the case too.

One thing you really need to watch out for! Moisture in an R134 system will corrode the hell out of metal parts!!

If I change to ES12 or Duracool, will I be able to find an auto ac shop who will vacuum out my system before I put in the new gas? I thought that most shops will not want to contaminate their vacuum machines.

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Paul 1987 300 SDL; 2000 ML; '69 MGB; '68 VW Fastback

IMHO, the only real solution is to find a good shop and have the R-12 system completely repaired, especially in AZ. I tried R-134a in mine and was not happy with the performance above about 90F. I wouldn't play around with "alternative" stuff unless you find a shop that is willing to service it.

How will their machines be contaminated by what you are going to put in your system?

I have not had this problem with Envirosafe or Duracool. I've been using these for two years and here in Phoenix where we see 120* summers, my dash vents produce 48* air at good fuel economy on both my 240D and my 300D. In fact I have yet to notice a drop in fuel economy with the AC running at max since I converted! This was not the case using R134A. My fuel economy would drop about 3 to 4 MPG with R134!

I really recommend both of these since no special licenses or permits are required because neither Envirosafe or Duracool are toxic, poisonous or damaging to the environment! Both are totally and fully compatible with refrigerant oils from both R134 and R12, but the oil for R12 works better in my opinion and this is still easy to get and use.

Both Duracool and Envirosafe are an easy to use friendly system to service yourself and leaks are easy to find with a simple ultraviolet light. A guage system used to install and charge with R134 will fit both Envirosafe and Duracool and the same fittings for R134A are required, so there is no reason for obsolete parts!

It may take a little longer, but the benefits of NOT using R134A and going with Duracool or Envirosafe are well worth the effort and when I turn on my AC in my 240D, there is NOT a big power drop with the system running at maximum!

Just curious, have you found someone who will service your system?

I service my system myself, but if I wanted to go get it serviced I would go to Penske Truck services since a lot of truckers use Duracool. I haven't had any problems asking for service here in Phoenix, but this is AC country!

Duracool has service centers in most every state and I would go to their website and ask which one is closest to you.

OK, I was just wondering. I'll stick to R-12, my indy can handle it and there is no downside to using the correct refrigerant for the system.