91 560SEL AC compressor/conversion
 

my AC compressor is leaking and now the system is 'flat' and will not even engage. I have an R12 system and was wondering if it is a good idea to convert to R134 given that I will need to get the compressor fixed. Also, is it worth doing a reseal on the compressor or buy a rebuilt one?

If you can keep the system on R12 then there is no need to convert to R134A. The system was originally designed for R12 and will yield better performance as opposed to R134A. Most people are not satisfied with the results of a conversion, even one that was done correctly. These cars just don't convert well.

As far as the compressor is concerned, you may be better off obtaining a quality rebuilt depending on how many miles your current one has logged. They do wear out eventually.

Statistically cars converted to 134, even a thorough conversion only last 2 years before serious attention is again required.

The cars requiring R12 are now quite old and hitting the wrecking yards or the crushers in record numbers. This has decreased the demand for R12 which of course has decreased the price. It is now available at prices not much higher than 134.

I have seen people spend literally $1,000 to convert to 134 so that they can save $50 or $60 on refrigerant. I guess I'm old enough that the math I learned was different from what has been taught in later years.

Stay with R12. Leave the 134 and worse yet, the junk refrigerant conversions alone.

So if you had a car that was converted to R134a, was working, but not quite as well as you would like would you back convert it to R12? How hard is it to get the R134a oil out of the evaporator? The compressor needs to be unmounted and cleaned out, right?

-Jason

I have reverse converted a number of systems with great success. The procedure is documented in numerous threads on this forum, but I will repeat it once again:

o If the system is not empty, recover the remaining 134.
o If there was a leak that led to service, repair the leak.
o Break all connections and flush all lines and components thoroughly preferably using a/c flushing agent, but Brake Cleaner or Mineral Spirits will get the job done. Blow the flushing agent through the line and then blow all of the flushing agent out of the line or component THOROUGHLY with compressed air.
o Remove the compressor and turn it by hand to empty as much oil as possible. DO NOT flush the compressor with flushing agent, use Mineral Oil for this purpose.
o Distribute the correct amount of Mineral Oil through the system by pouring a little in each component.
o Put the compressor back in place, turn it by hand at least a dozen turns to ensure that it is not liquid locked with oil.
o Lastly install a new r/d and don't do it until you are ready to immediately begin evacuation as soon as it is installed.
o Evacuate and charge the system with R12.

My conversion experience...
 

I went from R12 to R134a, as recommended by my (now obviously former) mechanic. There are two problems with the conversion:

1. R134a is not as strong as R12, i.e. it will not cool as well as R12 does.
2. R134a operates under higher pressure, meaning a tired compressor will fail more quickly, but worse, you will have a pretty much guaranteed expansion valve failure. Though the part is not expensive, shops charge an arm and a leg to do it. Also, tired hoses will fail more quickly.

I repaired the expansion valve myself, and replaced bad hoses. The compressor lasted three more seasons after the conversion before it became so weak that I swapped it out with a Denso rebuilt that was advertised as being R134a capable.

The A/C is working all right, but not as efficient. I have purchased a parallel condenser that supposedly would add about 10% or more efficiency into the system, but have not yet had the time to have fittings and hoses made to install it. For Washington D.C. thought, with the new compressor, new expansion valve, and so on, the conversion works adequately well.

For replacing the expansion valve, I did a writeup here. Shop wanted at at least $1,200 to do it, the part is about 40 bucks, and I did it in an afternoon, with the experienced help of my friend Chuck (a moderator of this board).

I don't get it! Why pay money for a parallel flow condensor and keeping going down this admittedly rough road? R12 is now in much less demand thus it costs only a little more than 134 these days. Reverse convert and solve your problems.

Nope - there I am not so free. Simple reason: wife! She is in EPA's upper management. So we are not touching R12....

What does her position have to do with legally using a refrigerant that was legally put in the car at the factory. Go online and take a test and get EPA 609 certification and buy the R12 LEGALLY. Does the EPA have a problem with you performing legal service on your vehicle using legally acquired goods and supplies?

You can take the test online in an hour or two at the most for a $15 fee.

I don't want to mess with it. Period. So I am keeping mine at 134a.

It's your money and your car. We are free in this country to do with our money and property as we see fit, at least to a point, and for now.

$1,200 is WAY too much money for changing the expansion valve. Since you are committed to following the EPA guidelines, I hope that you recovered the refrigerant when you did this job. If you vented it, that would be a violation.

As a reminder, to follow the Federal law, the system must have correct fittings and proper labeling. You must also use shutoffs in your gauge set no more than 12" from the port. This and further information is all in the 609 certification information. There are probably just as many or more violations of Federal law in converting and servcing converted systems than there are in handling R12. Since you are committed to following these laws, which is commendable, perusing the information online would be helpful for you.

Good luck with it.

Jeez maneeze! Just because I disagree with you on R12, you are laying it down hard.

I did not realize you had to evacuate the system after a blown expansion valve and a bad compressor hose. Wow!! I learn something new every day.

(think of the logic - of course the system was EMPTY! Blow expansion valves and bad compressor hoses lead to EMPTY SYSTEMS! But when I did do the compressor, I did have the R132 recovered professionally first. In fact, my new mechanic did it for free - he did not want the stuff floating around in the air!)

You obviously misunderstood. I don't disagree about R12, I am merely stating facts. Since you were committed to following the chapter and verse of the law, I was merely pointing out a few things that I thought you would want to make sure that you know.

Chill out.

looks like I am sold on retaining the R12 system. so, right now, due to compressor leaking, I am told that there is no R12 left in the system. The system now is 'Flat'. I plan on replacing the compressor, drier and expansion valves. Any tips on the procedure on how to go about it? I have dealt with a lot of DIY on my 91 560SEl but this will be the first time for an AC rebuild for me. After changing all parts do I still need to evacuate before it can be re-charged with R12?

There a a few re-built compressors sold on EBAY. Are these any good?

thx,

After a system is opened for service it must ALWAYS be evacuated, and THOROUGHLY so before charging.

The question would be whether or not the system needs flushing. Was the compressor only leaking, but working okay and without noise? If so, then you will not need to flush the system. Since it was originally R12 and if you know for sure that it has never had any other refrigerant then you are golden. Simply replace the compressor and r/d, add a few ounces of mineral oil, evacuate and charge.

I have used a few compressors bought on ebay with good success. Most of the MB ones can be had as a kit that includes the new r/d in the package.

Larry, thx for the response. so what's the noise got to do with flushing? I think you lost me there.

The system was working fine until one day some intermittent noise that sounded like the clutch trying to engage, then it would not engage at all. a quick check by an Indi verified that the AC would not engage because there was no freon. Further verified that compressor was leaking badly when tested for leaks.

any particular supplier in EBAY that you have used in the past?

My question goes to the health of the compressors innards. If it is healthy but it leaks, then you should have a clean system that will not require flushing. If when turning the compressor by the front clutch portion it feels rough or if it was noisy, then you may have debris from the failed compressor in the system to flush out. If that were the case and you didn't flush, then the debris would destroy your new compressor.

If it is only leaking, still turns smooth and made no noise, then you should be good to go without flushing.

I can't remember who the vendors were. It's been a couple of years since I replaced one. The main thing is that these compressors rebuild well as far as I know. There are some others such as the old R4 that should be avoided in rebuilt form.

One of the few I've read good things about the rebuilds from is Four Seasons.

I don't know who might carry them on eBay, but I did locate their parts on Amazon, and was surprised that they were at least reasonably priced, though not bargain basement cheap.
To find their part numbers, just use the catalog on the site, and then search the PN on amazon or ebay. Most don't seem to list the MB as an application on the ads, but it cross references on the manufacturer's site.
http://www.4s.com/Online%20Catalogs-eCatalog/Content.aspx

If the Four Seasons brand is good, then they have drastically improved over the last several years. They used to justifiably be called "Four Seizin's."

I'll qualify the statement with the disclaimer that I have no personal experience with the brand, though I was planning on ordering a pump, receiver drier, and expansion valve shortly, assuming that I can't find a shop that I trust to do a shaft seal replacement on my SD's R4 pump.
I'm also debating the virtues of converting back to R12 while I'm in there, but not sure I want to go to the effort of that thorough a flush, as well as expending that much of my limited r12 stock, not to mention trying to get the idiotic fittings off.

I got the info leading me to read up on Four Seasons from my father who is a fleet mechanic for one of the Oregon state fleets, and he's generally not led me wrong on auto maintenance topics.

any suggestions on where to get a set of R12 manifold gauge set? any reasonable vacuum pump to purchase or should I go for a rental?

I don't know if you are on a strict budget or not.

If you're on a budget R12 gauges can be had really cheap at garage sales, ebay or lots of places. This is something that's been produced for over fifty years and in the car world, virtually obsolete for many people.

For a budget vacuum pump, go to an appliance repair shop and they will sell you an old refrigerator compressor for probably $5. Solder a 1/4 inch inverted flare fitting on the inlet and you've got a decent vacuum pump. If you want to get fancy make a frame with a handle and weld a bung in the top so you can change oil. I used a pump like this with great success for a number of years before getting a single stage wet vane.

If you're NOT on a tight budget, there are numerous online sources for a/c tools. The one that I've found with best prices and good service recently is tooltopia.com.

Also if time means more than saving money, you can get all this at your local supply house that caters to the residential/commercial HVAC service trade. The gauges and vacuum pump are both exactly the same equipment that these guys use because it is also used on R22 and R502.

Hope this helps.

i saw this on ebay for $42 - guage with vacuum pump? is this complete set? or am I missing something? is this any good?

http://cgi.ebay.com/ebaymotors/R12-R134a-R22-R502-AC-MANIFOLD-GAUGE-SET-w-vac-pump-_W0QQcmdZViewItemQQhashZitem335d0d3fb0QQitemZ220604481456QQptZMotorsQ5fAutomotiveQ5fTools

That air-operated vacuum pump is not strong enough to evacuate an AC system. You need a oil-submerged vane pump, preferably dual-stage, but single-stage will be a whole lot better than the air-operated pump.

You might also see if any of your local auto part stores rent vacuum pumps.
I saw that at least one local chain does.

As to where to get R-12 gauges, I got mine off of Craigslist for $20.
I couldn't complain about it too much. No idea what brand, but they seem to be a solidly built set, marked as Made in USA as the only script other than the range markings.

are there any other parts that would make sense to replace while working on the AC? I will replace the ac compressor, drier and expansion valve. flush, evacuate and re-charge with R12 is also in order.

also, aside for the R12 canisters, is there some other oil that I need to add? how much R12 do I need to charge a 91 560 SEL AC?

I am in the process of re-charging R12, but now I am stuck and need some help.

Here is a summary of what I have done so far:

Replaced compressor (reman), drier, pressure switch and temp switch, and all o-rings under the hood.

I flushed the high side which came out clean. i then decided to leave the low side alone. I did not replace the exp valve. this could have been my costly mistake.

I put about 7.5 oz mineral oil in the compressor, and about 0.3 oz in the drier, then assembled them back in.

I pulled vacuum overnight, closed the manifold valves thereafter for about an hour and observed vacuum held with no problems.

I then started charging with the first can. After about 2 minutes with the first can charging and engine off, I observed the low pressure went up to 90 psi and high side at 40 psi. I noticed there was some more left in the can so I dipped the can in hot water and it continued to charge. at this point I am thinking the low side is showing pressure too high. I decided to proceed with the second can, turned the engine on and heard the compressor engaging, but no cold air. I did not hear or see the 2nd can discharging at all. I thought it is because the pressure inside the system is now too high compared with the pressure inside the can.

any insights would be appreciated.

larry, you mean open both high side and low side manifold? I am using the yellow hose of the manifold guage set to connect the cannister. If I open both sides, wouldnt the R12 also go the high side? I think I am confused. kindly explain further.

lol @ $1200 to convert to 134A, a mechanic sure ate well that month thanks to you. R12 is perfectly legal to own, use, and purchase.

I see the 12oz cans of R12 hit around $25/ea during the summer (ebay, CL, etc) as opposed to around $10/ea for the 134A at the auto stores. Over four cans you are spending a whopping $60 more for refrigerant when purchasing in the heat of the summer. Buy it off season and buy in bulk, you will save piles... like I do.

There is simply no good reason to convert these cars to a different refrigerant. I tried Freeze 12 in my 300SEL, so say it does not perform well is being nice.



My tools came from ACkits.com

I managed to get (3) cans (12 oz) to charge. the 4th one was taking forever, and i think there is still a little left. the site glass is still cloudy and lots of bubbles so I think I need more.

How many cans do I need for a complete re-charge for a 560 SEL?

I found it quite long for one can to charge. I had to use hot water to get the process going. And even with hot water, I was not able to get the 4th can totally consumed with more than 2 hours trying.

Capacity should be around 2.9lbs.

so should I go by the capacity spec or the site glass. it is impossible to measure how much actually got charged.

thx Larry. yes I did fine regarding the re-charging procedure. For (14) oz cans, I think you are right. it would take a little less than 3 cans. but for (12) oz cans that would be 4 cans to get 2.9 lbs. However, since it is not possible to measure the actual amount of freon being pumped-in, should I use the site glass as my indication that it is fully charged - when it is "Clear" and compressor is engaged?

I also noticed that even if the can feels empty by shaking it, there is still some pressure inside when releasing the tapper. so I think there will be some loss somewhere in the process.

yes Larry. I am on R12 system. my car is a 91 560SEL and I was using 12 oz cans. With more than 3 cans used, my site glass is still telling me I am undercharged. there is cooling inside the car, but I feel it still can get better.

How come it is taking so long to empty a can? I am guessing while the car is running, the ac pressure goes up therefore the pressure inside the can might not be high enough to push the gas into the system. this is where the hot water can help. but even then, the can does not get totally emptied.

just by memory,

with engine off, the low side = 90; high side = 120; ambient = 65.

with engine at idle; ambient = 80s; low side = 110; high side = 150

with engine at 2000 rpm; ambient = 80s; low side = 115; high side = 190

these are just my recollection.

The label on a 1989 560 SEL calls 2.9 lbs. The pressures listed in your last post are not ok. They could be ok if the system wasn't calling for cooling at the time the gauge readings were observed. A reading of 30 to 40 psi low and 170 to 200 high is wide range depending on other variables.

I can see the clutch turning when the ac is on. I there a way to isolate the cause one way or the other?

what are old fashioned service valves? and how is it used to diagnose the problem?

I noticed also that the AC compressor stays on (engaged) all the time while the AC system is turned on. It disengages when the AC is turned off. There is cool air inside the car. do you think it may be possible that the compressor is faulty (weak) and is unable to get the pressure on the low side to go down low enough to trigger the pressure switch to disengage the compressor?

Sounds like my logical next move then is to replace my exp valve. I will need to find a shop that can reclaim the R12 first, replace the exp valve, evacuate then recharge.

does this make sense? any shop you know in the San Jose area where I can have the R12 reclaimed?

I spoke with a local benz shop and with the symptoms that I have, he said it is either compressor, or exp valve or low on freon that could cause the problem. so since my sight glass is still cloudy, I will try and get some more freon to clear-up the sight glass and then observe if the pressures align to spec.

yes I have - (4) 12oz cans. however, the sight glass is still cloudy and with lots of bubbles. we are dealing with old cans here and we are not really sure if the net weight were indeed 12 oz per can. so should I follow the weight via the number of cans or should I follow the sight glass indicator?

after driving for a couple of days after the re-charge, I decided to hook-up the manifold gauge set again to check, and to my surprise the pressure readings are now within limits - Low side = 40-45; High Side = 150 at idle. I am puzzled as can be but am glad I am back on track. thank you for all the help and guidance.

I need to get me a thermometer to measure the vent temps. what pressures do you consider very good? I got those pressures while on idle for about 2-3 minutes after starting the engine. also the fact that the sight glass is still with bubbles(kinda pulsating spray pattern) might also indicate more freon is needed?

Well then use propane. Its even more efficient than R12 really cheap, and compatalbe with R12 mineral oil. Now, you need to do the charge yourself because its illegal for a mech. to do it. Why? Stupid government rules. R134a doesn't work well in a conversion because you need a larger condenser and evaporator due to the lower heat transfer rate of R134a. Propane is only slighly more flameable than R12 but, it will freeze your nads off!

here are some temp readings:
Car in idle, dahsboard outside temp reading = 87F; ac wheel = high; fan = high;
duct center vent = 55F

Car in motion, dahsboard outside temp reading = 75F; ac wheel = high; fan = high;duct center vent = 40F

Operating the recirculation switch will lower that 40 deg reading a small amount. Sight glass observations are helpful but the system pressures tell all. I have seen many systems running at optimum with a sight glass with flash gas running through it. Make the electric condensor fan is operating at the factory set point and the condensor is clean. It looks like you are on the right track.

Where is the A/C high pressure port
 

Where is the A/C high pressure port for a 1990 Mercedes Benz 560 SEL (W126)?

Thanks.

Open the hood and look at where the grille would be. It's on the right of the condenser.