A little help getting my A/C to work? - Page 3 - PeachParts Mercedes-Benz Forum

winmutt · #31 07-01-2009, 07:47 AM

Quote:

Originally Posted by dieseldan44

winmutt -

if I have no refrigerant in the system, how do I load in the dye with a 'test charge' of some sort to look for leaks?

Hook up the can, run the motor at 1500rpm and short the wires on the dryer.

Quote:

i know they have dye in a pressurized can. is that what i need? do I need to evacuate?

No need to evacuate you already had R134 in there, yes use the dye. Since it is likely there is little or know oil left you want to run it just long enough to circle the dye all around. Let it sit a day and then run the compressor the next day for a little bit and let it sit again. The idea is to build pressure, leak, build some more pressure, leak some more, then find the leaks. Once you find the leaks, flush and evac the system, put new oil and r134 in. Personally I recommend freeze 12, it is mostly r134 with a few additives and can be mixed into an existing r134 system without issues.

Quote:

Is there any way to test the compressor other than finding any leaks, fixing them, evac'ing, charging, and seeing what happens?

When you evac you pull a vac till it holds a steady pressure. Pretty good indicator of leaking or not.

leathermang · #32 07-01-2009, 01:10 PM

Gee Whiz, we keep going over the same things..
Dye is not a good idea. If your leak is somewhere hidden or dirty then you can not see it...if the leak is on the top side of a fitting it may not get there in a fashion which would cause it to come out.
Best solution all around ... which keeps the dye from potentially clogging any important tiny orifices...like the TxValve... is to put in 4 oz of R22 and charge the whole system with nitrogen. Then use an electronic leak detector to check for leaks... EVEN the evaporator hidden up in your dash can be the cause of a leak and that electronic detector will scream and point out that that is where the leak is.... if you use dye do you really think you will be able to see a leak up in that enclosed evaporator space ?
The EPA allows you to vent that 4 oz of R22 .... and it checks the system in the charged state... as compared to a vacuum only test which pulls the orings and checks them in a configuration which they will not be in when you are using the AC...
If you are smart you will stick to R134a or retrofit R12... Freeze12 is a blend and as it leaks out in the end of the compressor ( a planned leak for keeping that seal lubed ) it's composition will change... the lighter molecules leaving the system first...
And if you ever need your system worked on by a pro out on the road... just try finding someone who will work on it with Freeze12 or anything else which will contaminate their expensive equipment...
A compressor run venturi AC vacuum is not good enough for my system... and I suggest not for yours either... you already know that the correct tools are rentable in your area ...so be smart and do that.

dieseldan44 · #33 07-01-2009, 06:14 PM

leathmang,

I have heard of the R22 + nitrogen procedure from an AC tech. Can I get nitrogen in a can? How about R22?

I didnt see a refrigerant detector for rent. I have heard about dangerous procedures detecting refigerant with a propane torch.

How long does it take to R and R the compressor?

dd

#34 07-01-2009, 08:12 PM

Some time ago I was looking at getting dry nitrogen and rigging up for this trick. Since then I have gotten an Inficon Tekmate Leak Detector and have come to the conclusion that very few leaks require the Nitrogen/R22 trick. The modern sniffers are good enough that a simple charge with the correct refrigerant will almost always find the leak. Between a good sniffer and UV dye, leaks don't elude me any more.

The biggest advantage to the Nitrogen trick is that it will provide lots of pressure in areas that normally don't provide a lot of pressure to force the refrigerant out for detection. Since getting my Tekmate, I have yet to come across an elusive leak requiring the Nitrogen.

I have added so much a/c equipment to my arsenal of late, that a nitrogen bottle and regulator are about all that's left to purchase, so when that elusive leak comes along, I'll belly up to the bar and get the Nitrogen setup.

leathermang · #35 07-01-2009, 09:49 PM

Larry, this is not a trick. I know that if I say something you are naturally disposed to opposing it but MOST people do not have any way to recover the installed refrigerant if there IS a leak...

thus this procedure is designed to follow EPA rules about being able to vent the detectable chemical and have the system pressurized in a fashion which will encourage leaking... without undue problems ( taking out the refrigerant ) or expense in order to address whatever leak is found. The EPA wants to encourage fixing of leaks instead of ' feeding ' them... And the descriptions of the cases in which the dye is less than effective still apply.

DD, check your pm's... Greg

Matt L · #36 07-02-2009, 12:44 AM

Nitrogen would be good to have if you're changing components and want to minimize water contamination (to either the dryer or the PAG oil). Evacuate the refrigerant until you get the required 20" vacuum, then charge with nitrogen to a slight positive pressure. That way, air won't rush in when you disconnect the old component and swap in a new one.

dieseldan44 · #37 04-11-2010, 08:27 PM

So im going on a road trip for a month to the Southeast and Texas...

AC is now a requirement..not a luxury like it is here in the NE :-)

So Im back on the hunt to fix the issue. I re-read the thread which helped me remember what I had done. I have three weeks till departure...

I am going tomorrow to a friendly (non-MB) garage who said they'd help me out and work it through with me. Hopefully I don't have to replace the compressor, although I am mentally ready to.

Plan is to:
1.) Put belt back on AC compressor
2.) Go to garage and get their opinion...
3.) Probably replace Receiver/Drier, vac, and recharge with 134 while I access to the gear.

dieseldan44 · #38 04-12-2010, 05:15 PM

Went to the friendly garage (U-Do-It Autoworks in Nashua NH - great place - they let you rent a bay and a lift)

Here's what went down:

I described the situation and history to the owner/mechanic. He said that in New England, it's very common for cars to lose charge because the systems are not run in the winter, and are designed to leak a little bit to keep the seals lubricated.

We pulled the fitting off, and there was still 15 psi positive pressure in the system. When I said the car's AC had not been touched for at least 4 years, he said there is probably no big leak.

He pulled a deep vacuum on it while I put on the AC belt. Which of course took me 45 minutes to get everything back on an re-tensioned. Vacuum held fine.

Once that was done, started the car up, and he charged it to FSM spec using an automotive AC machine. 48 degrees at the vents.

So, compressor was good after all. It sounds fine now, it just needed refrigerant to supply oil.

It worked well on the ride home, but I wont really know till it gets hot. All I need is for it to work for two months to get through the trip, then it's OK if it goes out again and I need to do some more in depth seal replacement to get it to hold a charge long term.

My aux fan doesn't work. Time to diagnose that before Im sitting in TX traffic when it's 95 out.

And woah you can really feel the additional load when the compressor kicks on, even going 65 on the highway.

leathermang · #39 04-12-2010, 07:46 PM

Quote:

Originally Posted by dieseldan44

Went to the friendly garage (U-Do-It Autoworks in Nashua NH - great place - they let you rent a bay and a lift)

it's very common for cars to lose charge because the systems are not run in the winter, and are designed to leak a little bit to keep the seals lubricated.

We pulled the fitting off, and there was still 15 psi positive pressure in the system. When I said the car's AC had not been touched for at least 4 years, he said there is probably no big leak.

He pulled a deep vacuum on it while I put on the AC belt. Which of course took me 45 minutes to get everything back on an re-tensioned. Vacuum held fine.

Once that was done, started the car up, and he charged it to FSM spec using an automotive AC machine. 48 degrees at the vents.

So, compressor was good after all. It sounds fine now, it just needed refrigerant to supply oil.

I am glad it is fixed...
this is probably a good time to restate some of the principles involved for others in similar situations...

"it's very common for cars to lose charge because the systems are not run in the winter, and are designed to leak a little bit to keep the seals lubricated. "

The manual suggests starting the car AC once per month even in cold weather so the designed leak at the compressor shaft can lube that seal so it does not leak more than desired refrigerant out.

It sounds like you did not take out the old oil due to thinking that the residual 15 lbs pressure meant that no moisture could have been sucked into the system.
This is not correct or safe procedure since as a dynamic system when the compressor it working it is possible ... even likely .... that a leak in the system other than that at rest leak at the compressor shaft will pull in air/moisture compromising the oil and creating acids which can attack metal parts... finally causing flakes to come off and clog important small openings like the TxValve....
What makes me suspect that it might have been a larger leak is the fact that the belt was taken off of it four years ago.... seldom is the belt taken off unless it is not working. it can be.. I am just playing the odds....
A vacuum can only be so deep... which depends on the barometric pressure and temperature extant that day... in general industry standard recommendations call for more time under vacuum than forty five minutes...
It is a slow process to boil moisture out of the oil in the lines... and NONE can be boiled out of the receiver - dryer...as that is a deep oil pool with silica jell to capture and hold moisture as it goes through the system..
STANDARD procedure is to replace that under sketchy circumstances... and the fact that the PO says another AC shop could not fix the problem puts your system into that category in my thinking...
The bad part is that if I am right you will not have the bad things happen for months or years...
An oil evacuation/ flush, new Receiver-dryer might have been good insurance for long life...
Also, was R 134a available when your car was new ? How he charged it to " FSM " specs I am not sure... sounds like he interpolated the readings...and 48 degrees at the vent ( assuming forced air at the condensor, not in sunshine,AC on MAX reading BUT SLOW fan ) probably should have read lower than that....
It will probably do fine for the period you need in TX... then the pressure will be off and if you see any signs of deterioration ... or just have a chance to study the situation more you could do these same things after you get home..
Where in Texas are you going to be ?

dieseldan44 · #40 04-12-2010, 08:40 PM

Quote:

Originally Posted by leathermang

What makes me suspect that it might have been a larger leak is the fact that the belt was taken off of it four years ago.... seldom is the belt taken off unless it is not working. it can be.. I am just playing the odds....

I took the belt off last summer when I couldn't get it to work. The belt was on there before. PO's mechanic couldn't get the system to run because he failed to properly diagnose the failed OVP relay (which I replaced to get the tach working)

Quote:

Originally Posted by leathermang

STANDARD procedure is to replace that under sketchy circumstances... and the fact that the PO says another AC shop could not fix the problem puts your system into that category in my thinking...
The bad part is that if I am right you will not have the bad things happen for months or years...
An oil evacuation/ flush, new Receiver-dryer might have been good insurance for long life...

I asked these questions at the time. I had a new R/D in hand - he said not needed since the system was not open. Said the same thing about the oil - and that PAG oil does not become corrosive like mineral oil.

Keep in mind I am paying for the time renting the garage space, so if anything, the gentlemen is motivated to have me in the bay as long as possible. And it's hard to argue with the guy who has 30 years experience and is working the controls of the machine I need to get the A/C working

even if you know its not totally 'by the book'.

Quote:

Originally Posted by leathermang

It will probably do fine for the period you need in TX... then the pressure will be off and if you see any signs of deterioration ... or just have a chance to study the situation more you could do these same things after you get home..

This is what Im going to do...once I get back and have some time this summer. Now that I know the compressor works and there aren't any gaping holes in the steel lines (happens often in the north).

I'll open the system up, give it a full flush, change all the o-rings to green ones, and recharge it. There's A LOT to be said about at least seeing this procedure done in person once. Now its not nearly as scary - it scared the heck out of me to try charging without help for the first time with the system in an unknown state.

For better or for worse, I know the 'state' of the system now. I know a couple steps were skipped today. But, based on several techs Ive talked to up here, this is how they all do it. It must be a Northern thing since people don't rely on the A/C as much. Or maybe they like the repeat business?

Quote:

Originally Posted by leathermang

Where in Texas are you going to be ?

Austin, San Antonio, Corpus Christi and Houston at least. I'm going on sort of a 4 week tour of the SE US, and plan to spend a lot of time in TX - Ive never been. I have relatives in SA, a friend in CC, Ive always wanted to see Austin, and business in Houston.

#41 04-13-2010, 01:33 PM

Did you check the system for leaks after charged? Did the guy have a sniffer? Under the circumstances, the presence of a leak would not be at all a surprise.