evaluating an AC compressor when system is currently discharged - Page 8 - PeachParts Mercedes-Benz Forum

kuene · #**106** 05-22-2018, 07:01 PM

My old drier had a pressure relief valve. The new drier (berh, purchased from pelican as the compatible part for my model/year) does not. So I’m asking if I’m supposed to add a pressure relief valve, or do I have the wrong drier? I don’t believe there is another relief valve anywhere else in the system.

Shucks, I have the blue nylog, as I read in a few places it was compatible with all refrigerants, including r12. While I have a supply of r12, I’ll probably pressure test/rub system with r134 first, and maybe end up converting down road if any problems. I’m not going to plunk down so much money for another 2+ pounds of r12 if I’m chasing leaks. If it’s safe to use, I’ll probably put it on the two bottom exp fittings there were not hell to get threaded.

lukaskupasz · #**107** 05-23-2018, 03:48 AM

Every time my compressor shuts down it makes a loud bang (or clank) noise. Is this a symptom of something I need to deal with?

The compressor was replaced seven years ago and the system is doing a great job of cooling.

kuene · #**108** 05-23-2018, 09:13 AM

I’m going to nylog all the orings. I don’t see how nylog in the threads would help - aren’t the orings doing all the deal work?

In any case, as I get close to having everything back together and putting in the new drier (still wish I knew if I needed a pressure relief valve) this weekend, I’m looking to then test the system with r134a. Both pressure test and maybe just see if the system works/cools a little. For that reason, I’ll ditch the r12 mineral oil in favor of ester oil. About how many oz of r134 would I need to pressure test?

Charging from these cans is going to be a whole new learning curve. Another reason why I want to use r134 first with the sis can tap - this way I have some practice before puncturing the r12.

Diseasel300 · #**109** 05-23-2018, 10:33 AM

Nylog acts as a lubricant in addition to its sealing qualities. Adding it to the threads helps the nuts tighten down better, it also adds a secondary layer of leak protection should the O-rings begin to weep. Just one of those "While you're in there with it in your hand" things.

Ditch the pressure relief. Does it need to be spelled out? It's an unnecessary part. Delete it. It's just another (highly probable) leak point.

If you're gonna charge with r134a, you may as well charge the system and test it out. 80% by weight of the R12 capacity for your vehicle.

kuene · #**110** 05-23-2018, 02:42 PM

Thanks diseasel. Sorry bout the multiple relief questions, I was just not comprehending. Got it now!

Now if I can just get to this one buried hose connection on the high side I will have replaced all the orings. I’m in way deeper than I started but thanks you you fellas (some of you may be ladies too) I’m feeling pretty confident I’ll get this bad boy cold Or I’ll just push it in the lake.

vwnate1 · #**111** 05-23-2018, 10:05 PM

Don't get discouraged ! .

Many Mechanics learn by doing just as you're doing .

Take things slowly, you'll either get it or maybe have to try again .

The satisfaction you'll get from doing anything with your own two bloodied and bruised hands is indescribable .

Rome wasn't built in a day, your old Mercedes wasn't worn out in a day either .

Relax and take is slow .

kuene · #**112** 05-26-2018, 09:20 AM

Is this Ester oil good to use in my system? https://photos.app.goo.gl/BZ5D29JGhCQKwVPP2

Remember I’m using r12 for now but possible I’ll move to r134 - so I want an oil for both.

97 SL320 · #**113** 05-26-2018, 12:03 PM

Quote:

Originally Posted by Diseasel300

Ditch the pressure relief. Does it need to be spelled out? It's an unnecessary part. Delete it. It's just another (highly probable) leak point.

The pressure relief is there to prevent over pressure on the high side if the orifice tube / expansion valve won't pass freon or if air flow through the condenser has stopped / is too high. It's also there in case the system is overcharged. Yes, I'm aware that sealed systems like a fridge do not have a pressure relief,however these are made of hard piping and can stand higher pressures.

Over pressure can cause a hose to burst , compressor clutch to slip. Think of the pressure relief as a fuse in an electrical system or an over pressure relief on an air compressor.

132 does operate at a higher pressure so this would need to be taken into account when converting from 12.

funola · #**114** 05-26-2018, 12:26 PM

The AC compressor should have a pressure relief valve. If not, then I'd make sure there is one elsewhere in the system.

BillGrissom · #**115** 05-26-2018, 12:29 PM

Quote:

Originally Posted by kuene

Is this Ester oil good to use in my system?
Remember I’m using r12 for now but possible I’ll move to r134 - so I want an oil for both.

I use Hella's PAO 68. You can buy on ebay or as Duracool's Oil Chill. It works w/ all refrigerants, mixes w/ mineral oil, doesn't absorb moisture like PAG, and makes the AC system run more efficiently. I wouldn't switch to R-134A since being outlawed. It is a nasty "climate change" gas. The EPA should have stayed w/ R-12, unless the "ozone hole growing" theory was correct (read up).

97 SL320 · #**116** 05-26-2018, 03:56 PM

Quote:

Originally Posted by BillGrissom

I wouldn't switch to R-134A since being outlawed.

Only for use in newly built equipment, the actual production of 134 will be unaffected. The "newly built equipment" apparently only includes light duty vehicles. 134 is used in stationary systems and there isn't any mention of a ban there.

https://refrigeranthq.com/does-r-134a-have-a-phase-out-date/

Quote:

As of the year 2020, or 2021 model year, light duty vehicle manufacturers will no longer be able to use R-134a in their new automobiles. The mandate does not say what they have to use instead but there are very little choices to choose from. Most manufacturers will end up going with the HFO refrigerant known as 1234YF. This new refrigerant runs very high in price at about $700 per ten pound cylinder compared to the $120 for a thirty pound cylinder of 134a.

So, to answer your question the phase out date for R-134a is set for 2020. However, with that being said there is one important thing to point out. Unlike with the CFCs and HCFCs phase-outs of the past the R-134a phase-out is not seeing a mandatory reduction in imports or production. What this means is that supply of R-134a should more or less remain the same but the demand is going to start shrinking and shrinking with each passing year. When we go above and beyond the year 2020 I could see the price of R-134a plummeting.

kuene · #**117** 05-26-2018, 04:05 PM

Didn’t realize until putting on that my heavy r4 has bigger Pully wheel than my old compressor. So looks like i a need a new belt. The circumference of the heavy r4 pully is about an inch or so more than the old r4. Anybody know how I should go about sizing the replacement belt? I could bring in old one and make a purchase relative to its size maybe?

ROLLGUY · #**118** 05-26-2018, 07:36 PM

http://www.tirereview.com/understanding-the-differences-between-ac-compressor-oils/

http://www.behrhellaservice.com/behr-hella-service/assets/media/2015.07.16_PAO_Oil_68_from_Behr_Hella_Service__safe_and_powerful.pdf

kuene · #**119** 05-28-2018, 11:07 PM

Update - I got everything back together and for the first time since I've owned this car - cold air! Thanks fellas for all the help.

I'm running it on r134 for the moment, as I wanted to use that to test system before blowing all my r12. I calculated about 80% of the specified 2.6 pounds for r12. Seem right? Was 80 degrees on Sunday and I got nice cold air.

I'm not sure if my manifold gauge is leaking a very tiny bit - I'm also not sure if the pressure on the system would go down a bit at night if it changed temperature by a lot. I have uv dye in the oil, but I had a bit of a mess yesterday installing compressor and spilled out like 3-4 ounces on me - needless to say I've had a hard time cleaning all the dye up in places I touched, so leak testing via UV is not that helpful at moment, until I wash it all down in there. Before I charged I put in new shrader valves with little nylog - in fact got nylog on everything except for a couple spots on the exp valve. I can confirm there are no UV leaks from there.

Lesson be learned, when you front is up on ramps, and you fill up compressor with oil, but have a plate capping it until you are ready to attached manifold - it will all drain out when you remove the cover plate. so i had to guesstimate and hope that I added enough oil back in - I syringed it in at the top of the low side line.

In any case - when I finally got the new heavy r4 compressor on there, I realized after some struggling with belt and trying to fit manifold on that my old belt was too small. Duh. The four seasons heavy r4 has a clutch with a circumference about an inch larger than the compressor I had on there before. So I went from about a 36 in belt to a 37 and with the tension adjustment play I was able to get it on and setup.

Seems to work well, but is it OK on my engine and pullies and whatnot to be running a bigger/heavier compressor than factory stock?

I'll run this for a few days more where I can test out with hotter ambient temps. I'm really hoping I don't have to totally flush out the systems if I want to evac this r134 and put in r12 - would I absolutely need to if I have new ester oil in there (I fully flushed everything during this rebuild)? Of course I would pull and hold a vacuum in between.

funola · #**120** 05-29-2018, 04:39 PM

Congrats on cold AC! Did you replace all hoses as recommended by RG? I'd run it with R134 for the summer and see if it cools acceptably and only change to R12 if not acceptable.

Regarding your heavy R4 having a bigger diameter pulley than the light R4, I measured mine. My heavy R4 pulley is approx 5.125" in diameter, same as my light R4. The heavy R4 has a clutch winding housing that is a little bigger in diameter than the pulley. You have to get the belt over the bigger diameter housing first before getting it on the pulley, that does not make the pulley diameter bigger.