A/C - help trouble shooting, fixing - Page 2 - PeachParts Mercedes-Benz Forum

vstech · #1 04-27-2010, 03:23 PM

Quote:

Originally Posted by GreenMedallion

Here is what seems like a good game plan -

1) evacuate/flush system
2) replace expansion valve
3) recharge w/ Freeze-12
4) hope I get cold air!

Since I am pressed for $$, would there be any harm in skipping 1+2 and just trying to recharge the system? Would be only possible loss be a few cans of Freeze-12, or would that cause other damage?

um, no.
the flush will remove any oil from the lines/coils.
there will then be no oil to speak of in the system, so putting fr12 in there will kill the compressor in just a few minutes...
IF you are set to use fr12, you better get a complete kit with oil designed for the refrigerant blend. and you better put large warning stickers on the car showing freeze 12 blend is installed in the system!
I would do this order.
1 flush and clean lines and coils.
2 replace the expansion valve.
3 pressurize with dry nitrogen and verify leak free system.
4 replace receiver/drier
5 add correct volume of correct oil to lines for the refrigerant used.
6 evacuate system to 1000 microns or a solid evac if no micron gauge is used.
7 recharge with correct volume of refrigerant.
8 start system and test operation of blower, aux fan, and check system operation.
9 enjoy cool a/c

leathermang · #2 04-27-2010, 01:31 PM

" HOPE " is not really one of the concepts we use for dealing with AC systems... as they are really about pure physics. If you violate a rule it will bite you either with having to do it over again, or blowing your compressor or something else which will waste time and money ...
One was great.
Two can probably be skipped if it is clean.. however, to do a proper flush you will want to use the old expansion valve as a ' tool' and so you will need a new one.
Three is a very bad idea.. lots of threads about alternative refrigerants..
USE either R12 or R134a.
If you are ready to accept those premises post and let us know.. we can get you to where you need to go in a logical manner... and will strive for ' as cheap as possible ,but not cheaper )... in other words... you can shoot yourself in the foot trying to cut too many or certain important corners..

leathermang · #3 04-27-2010, 03:49 PM

John, number three needs to be expanded to give the whole concept..

"pressurized with nitrogen and four oz R22 and verify by using electronic detector "
that is the EPA approved method which allows the test nitrogen to be vented to atmosphere to continue with the job...

Everything else looks great..

but I am willing to be bolder about the Fr12... or other blends or hydrocarbons....

FOOLISH MOVE to use anything else except R12 OR R134a.
with it flushed and new oil and the correct amount of oil ... either of these are the best bet... if in really hot/humid area.. R12 .. if willing to upgrade the system some R134a fine.....

leathermang · #4 04-27-2010, 11:50 PM

Which ' Dealer ' did you work for ? So the smart people can avoid it....

69shovlhed · #5 04-28-2010, 08:34 PM

Quote:

Originally Posted by leathermang

Which ' Dealer ' did you work for ? So the smart people can avoid it....

american service center, and euromotor cars. both large mb only dealers. and all the techs do it that way, in every mb dealer i've ever heard about from all the mb certified techs which i have worked with for the last ten years. you do not have a clue. i am an mb certified master tech by the way. i do have a clue. i really didn't want to have to let that out.

vstech · #6 04-28-2010, 09:28 PM

wow, it's interesting to read what a "certified MB mechanic" thinks is a proper way to service a/c system!
I am sure your way is fine for your shop, but for those collectors and restorers of fine cars, we want it as close to factory long lasting cool as possible!
r 12 is approximately double to triple the cost of 134a. needing less than 3 lbs to fill a car, that's maybe a 30.00 difference in cost of refrigerant. hardly "very" expensive.
New 30 lb cylinders of 134 are around 90.00 to 200 new 30 lb cylinders of 12 are between 350 and 550, depending on the season. and for us enthusiasts, it's easy to find old stock cylinders for less than 150.00
old cars that have been running with god only knows what in them, need flushed clean lines. and it's just plain silly not to replace the dryer and the expansion valve when reconditioning a 20+ year old a/c system!
your shop needs to get work in and out fast to make money.
we want our cars to last forever, not just the seasonal work for the shop's profit.

69shovlhed · #7 04-29-2010, 05:44 PM

actually, i would probably recommend replacing the dryer, and we did put r12 in the older cars unless the owner wanted to switch to 134. we know r12 is bad for the environment, but some people don't care about that. i would never put r12 in my cars, and wish the govt would just ban it. but before i put a new expansion valve or dryer on a car, i'd want to know if the compressor worked. if the compressor is grenaded, you will ruin the parts you install when the compressor fills them w/ shrapnel. and even flushing the system is useless if the compressor is coming apart. granted i work on mostly newer cars. regardless, i'd evac and recharge w/ dye, then retest the system. if it works, your done. if it don't work, then you re-evac, and flush and replace parts as required. it may be your experience that the old expansion valves require replacement after a certain amount of time. but i can't see replacing it before you even know what's wrong with the system. for all we know it might already have a new expansion valve and dryer.
do you really consider these old clunkers to be "fine cars"? now i like my td, but it's not a fine car, never was, never will be. its a slow pig that wallows around corners, with a joke for a stereo. its not nearly as fun to drive as a gas car w/ a decent engine and suspension, but it does what i need it for. maybe the guy who started this thread has plenty of extra money and loves to tinker w/ stuff to see what will happen. but i think the best way to find out whats wrong (if anything) w/ the ac system is to get it goin and see what happens. any shop i've ever worked at will not charge you twice for the evac and recharge, and your gonna pay for an evac and recharge anyway if you want it to work. unless i see a reason to replace a part before i begin testing, i don't recommend any parts until i know exactly what needs to be done. and it might just have a very small leak.

leathermang · #8 04-29-2010, 06:08 PM

How do you flush the evaporator ?

69shovlhed · #9 04-29-2010, 08:36 PM

Quote:

Originally Posted by leathermang

How do you flush the evaporator ?

seems to me they had a special chemical to run through the system. i haven't had to flush an ac system in quite some time. the new compressors don't pop often; most of the problems i've seen were leaks. and yeah the dye don't help much if the evap is bad, but sometimes the leak is so big the dyed pag oil runs out the drains in the trans tunnel.

leathermang · #10 04-29-2010, 09:40 PM

Have you read the MB Factory Shop manual for the AC systems type one,two and three which applies to these cars ?

So the only time one needs to flush the system is if the compressor ' pops ' ?

What does R134a smell like ?

How small of a leak of R134a in the evaporator can you personally smell ...or did you have a dog ( German Shepard ? ) trained to detect that ?

69shovlhed · #11 04-29-2010, 11:54 PM

never read the shop manual. we have "WIS" at the dealer for work instructions. if the system has not been left open, and no components have come apart, i don't think flushing would be necessary, although i have heard that you don't want the old oil mixed w/134. 134 has a stink to it; i don't know how to describe it, but if you've smelled it on several cars w/ evap leaks, you'd know it.
as far as the dog, if i had one i'd train it to bite smart a$$es. if the leak is that small, how would you find it? fire up your crystal ball, or do high nosed types such as yourself have the olfactory capabilities of said sheppard?
standard procedure is to tell the customer that: if we can't find the leak w/ the dye and UV light right away, bring it back in 1000 miles or at your next service and we will recheck it. on many cars, the leak is so small that you can charge it up in april, and by the time it stops cooling summer is over and you won't need the ac until next year. i guess its different down south, but up here you'd find that alot of cars end up being recharged every spring and it works through the summer.
my td was converted before i got it, it works except some fool shimmed the clutch wrong and it slips a bit. i am gonna try to unscrew the plate w/ a spanner wrench, but the center stud is pretty rusty, may be seized on there.

leathermang · #12 04-30-2010, 12:22 PM

Quote:

Originally Posted by 69shovlhed

never read the shop manual. ..... if the leak is that small, how would you find it? fire up your crystal ball, or do high nosed types such as yourself have the olfactory capabilities of said sheppard?

It is obvious that you have not read the Mercedes Benz Factory Shop Manual for Air Conditioning... your answers make that clear... crystal ball clear in fact.

If I had a leak that small....which I did in my 81 TD ... I would use an electronic leak detector to find a leak in the evaporator. Since air is being forced across that whole area it works great... even better than most other areas which are out in the open.

rrgrassi · #13 04-30-2010, 03:39 PM

Quote:

Originally Posted by leathermang

It is obvious that you have not read the Mercedes Benz Factory Shop Manual for Air Conditioning... your answers make that clear... crystal ball clear in fact.

If I had a leak that small....which I did in my 81 TD ... I would use an electronic leak detector to find a leak in the evaporator. Since air is being forced across that whole area it works great... even better than most other areas which are out in the open.

I agree with the evap leak...who wants to breath in R-12, R134a, etc.

leathermang · #14 04-30-2010, 09:27 PM

Quote:

Originally Posted by rrgrassi

I agree with the evap leak...who wants to breath in R-12, R134a, etc.

My main point on that is that a leak can be way larger than one would want to charge a system with and lose the refrigerant..
but way smaller than one could detect by ' smelling' it... if in fact it can be smelled... if it is a big leak it may be the oil mixed with it which can be smelled..

69shovlhed · #15 04-30-2010, 10:44 PM

Quote:

Originally Posted by leathermang

It is obvious that you have not read the Mercedes Benz Factory Shop Manual for Air Conditioning... your answers make that clear... crystal ball clear in fact.

If I had a leak that small....which I did in my 81 TD ... I would use an electronic leak detector to find a leak in the evaporator. Since air is being forced across that whole area it works great... even better than most other areas which are out in the open.

didn't need to read the manual. WIS is the mb service program for dealer techs. it has everything they've ever put out since like '91 to service their cars. sounds like they've always had problems with crappy evaporators. the 140's were the worst, just about every one of those turds needed at least 1 evap replacement. we found that they would blow out big time; it was generally obvious when the evap was bad. it very well could be the pag oil which we smelled, but bottom line, you can frequently smell it when the evap is toast. but what does this have to do w/ the original post? yeah he may have an evap leak, but how is he gonna find out if he don't fill it up and check it out?
there are hundreds of dealer techs that do it the same way i do. that's where i got this procedure from, and it works good.
and i've not once seen dye clogging any part of the system on hundreds of cars over a 10 year period. thems the facts, jack.