Pulling an A/C System Vacuum - Page 2 - PeachParts Mercedes-Benz Forum

vstech · #16 06-03-2009, 12:19 PM

Quote:

Originally Posted by leathermang

They knew those hoses needed to withstand pressure in both directions..

As to purging the lines... that is the proper procedure.... but sometimes hard with the new ( self sealing ) ends mandated on some hoses... I would like to know how to purge them if someone knows... without freezing the end of a finger of course... Do you have to make some jig for this procedure ? I can imagine one.... but hope someone has a better way than having to make one...

... the sealing end hoses do not seal on both ends of the hose... to purge the hoses, just loosen the other end of the hose...

tobybul · #17 06-03-2009, 12:26 PM

Quote:

Originally Posted by slk230red

I just connect my vacuum pump to the gauge manifold so I can read the vacuum. After sufficient vacuum time, shut off the valves, disconnect the hose from the vacuum pump, connect the freon, charge the system.

Well, you are suppose to make sure first that the system will hold vacuum. Simply pulling vacuum will not suffice. After turning off your vacuum pump, the system should hold the vacuum for at least one hour or more.

If it does not, you will be wasting charging it.

leathermang · #18 06-03-2009, 01:38 PM

I believe that it is really necessary to charge the system to check for leaks.... because this puts pressure on the orings in the actual ' working' condition they will be facing...

VSTECH, I am not sure what you are saying ... the end away from the manifold with the gauges is the one with the sealing end ... thus if you loosen at the top you are not then ' purging' the line... am I off on my visualization of the situation ? My feelings are that you have to push the air out with the refrigerant for it to be legit ' purging'... ?

Ken300D · #19 06-04-2009, 09:28 PM

Thanks for the help - the answers take care of my worry on this issue. I was thinking of the hard plastic lines that MB uses in their vacuum system for the doors, etc., and thought maybe the softer A/C gauge line might collapse with the vacuum I'll be pulling through it. I sure would hope my nice new vacuum pump pulls more vacuum than the pump on the MB!

I'll surely have more questions throughout this job. Not sure whether to continue to post in this thread or open another - so I'll try here.

The new compressor. Will it come with oil in it? If so, is everything set up for R-134 these days? I plan to revert back to R-12 and will be flushing out everything on the car not being replaced. The condensor will be new as that has a failed seam. The compressor has been making noise and the clutch slipping, so I am replacing that as well. Doing the evaporator and receiver dryer also.

Will I need to flush the new compressor to set it up for R-12? What has been your experience? Is there any information with new compressors to indicate whether they are "set up" for R-12 or R-134, or are they all minimally lubricated from the factory? (Compressor is new, not rebuilt.)

Ken300D

Matt L · #20 06-04-2009, 09:41 PM

You do not want any PAG oil in the system at all, so it must be flushed. The compressor is unlikely to be shipped dry. You will have to drain as much oil out as you can, then flush the compress or with a LOT of the oil that you're going to use. I would use mineral oil. To flush the compressor, hold it in a vise and pour oil in the inlet, turn the compressor no more than 100rpm for a number of turns, then drain the outlet. Drain the oil from the crankcase and pouring new oil in there if you can. Repeat until the oil is all changed, which will be a while. You may have to run a half-gallon of new oil through the compressor, so get plenty. Never use any solvents to flush the compressor.

Yea, the AC vacuum pump will create a much lower pressure than your MB pump. But a vacuum doesn't pull. The atmosphere pushes. The line only has to withstand 15psi negative pressure, compared to ambient.

leathermang · #21 06-05-2009, 10:08 AM

Quote:

Originally Posted by Matt L

Yea, the AC vacuum pump will create a much lower pressure than your MB pump.

For newbies this term might be confusing... in this sentence Matt is using the ' AC' to mean alternating current... the actual car Air Conditioner does not have a vacuum pump... the CAR does have a vacuum pump associated with the ENGINE because a diesel does not naturally produce enough vacuum to be useful for the items in the car like the power brakes.
So he is talking about the 'plug into the wall vacuum pump' used to take the moisture out of the Air conditioning system in the car...

Matt L · #22 06-05-2009, 10:12 AM

Actually I mean "vacuum pump made for air conditioning use," but yes, I mean an electrical one. Those vacuum-powered jobs aren't powerful enough to remove water, and your engine pump won't pull enough to even cool very well.

So while I didn't really mean alternating-current, that's really the only kind of pump that will work here.

leathermang · #23 06-05-2009, 11:08 AM

LOL, I did not even think about the venturi air compressor run types when I read that...having dismissed them mentally as not able to do the job long ago.

Ken300D · #24 06-05-2009, 03:26 PM

On filling the R-12 system, is there any advantage to using the synthetic Frigi-Quiet?

I read somewhere that FQ is good by itself in R-134 systems, and as a "top-up" oil in R-12 (meaning that when you lose some charge and oil in an R-12 system, you "top-up" with Frigi-Quiet).

I realize this is something like the motor oil wars, but would appreciate your thoughts on whether Frigi-Quiet is appropriate in the R-12 system (in some proportion to mineral oil), or if I should just use 100% mineral oil. I have a supply of FJC refrigration system mineral oil already ordered, and am considering what to do with respect to Frigi-Quiet. The marketing is good and the general opinions on the forum are good on FQ.

Ken300D

Ken300D · #25 06-05-2009, 03:32 PM

A quote from my internet research:

"All Sanden compressors are delivered with PAG (polyalkaline glycol) oil. PAG oil is compatible with all common refrigerants including R-12 and R-134a. No flushing is required."

http://www.rparts.com/Catalog/Major_Components/compressors/sanden/sanden.asp

I'm not buying the Sanden brand, but came across the above quote describing the oil delivered in their compressors. I'm not sure I believe that quote.

Ken300D

leathermang · #26 06-05-2009, 05:29 PM

I suggest you use Castrol premium mineral lubricant for R12 ac systems cold flow 500.

gschira · #27 06-05-2009, 09:22 PM

If you suspect the system to be "low" of freon, how much freon R-12 should go in there. Also how much oil. What determines all this. Will the product mentioned earlier (Frigi-Quiet), work for this or not? Where is the best place (cheapest) to get the freon? Thanks for the good info y'all.
I am an AC newbie............

whunter · #28 06-06-2009, 02:07 AM

Quote:

Originally Posted by Matt L

Actually I mean "vacuum pump made for air conditioning use," but yes, I mean an electrical one. Those vacuum-powered jobs aren't powerful enough to remove water, and your engine pump won't pull enough to even cool very well.

So while I didn't really mean alternating-current, that's really the only kind of pump that will work here.

I disagree.
Vacuum is vacuum, regardless of how it is achieved.
The condition/quality of the vacuum pump is important, 28 - 30 inches mercury vacuum is good.
Most air powered vacuum pumps require a high volume commercial air compressor with a steady 90 psi line pressure to function properly = IMO very cheap to buy, but high cost of operation.
My 1985 300SD vacuum pump pulls 29 inches, and has been used for this job several times, (my objections to this procedure are: #1. The pump vents into the engine crankcase = possible oil contamination. #2. Damaging old vacuum lines. #3. Running the car for hours unlocked/unattended. #4. wasting fuel. #5. Difficult to carry a diesel engine around in a garage just for the vacuum pump.)..
Depending upon the condition of the system being repaired, a duration of 1 - 24 hours vacuum will remove all moisture..
A powerful high volume pump is faster than a low volume pump.
My favorite infinitely replaceable pump is in the following thread.

FYI: Free vacuum pump for testing.
http://www.peachparts.com/shopforum/showthread.php?t=88008

Most commercial refrigeration technicians use these vacuum pumps.
http://images.google.com/images?q=refrigeration%20vacuum%20pump&rls=com.microsoft:en-us&oe=UTF-8&startIndex=&startPage=1&um=1&ie=UTF-8&sa=N&hl=en&tab=wi

FYI note for beginners:

If the system was left open = disconnected lines not capped, road grit will need to be physically flushed out, and the receiver/dryer replaced.

If the system was left open and submerged in water, expect severe internal corrosion/contamination of the compressor, receiver/dryer, and expansion device.

Breaking open a pressurized system is dangerous, referigerant can burn lung tissue.
http://www.google.com/search?hl=en&rls=com.microsoft:en-us&ei=wgYqStXRO5fKMtPPrNYJ&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=refrigerant+burn+lung+tissue&spell=1

Have a great day.

leathermang · #29 06-06-2009, 10:08 AM

Well, I have to admit that that is the first time I have heard of anyone suggesting using the CAR's vacuum pump for evacuating the Car's AC system !!!

Almost a ' Boy Scout' or ' Survivalist' mentality to use the available resources to fix the problem. I really appreciate that.

I am particularly pleased at the fair assessment and presentation of the potential downsides Roy included in the post.

The QUALITY of the vacuum ( along with some persistence of application , ie, leaving it hooked up and running long enough ) is the most important item.

So, all in all, I suggest that if a person does not own a 'reasonable ,regular AC AC pump' that they borrow one or rent one.

Matt L · #30 06-06-2009, 11:40 AM

Quote:

Originally Posted by whunter

I disagree.
Vacuum is vacuum, regardless of how it is achieved.
The condition/quality of the vacuum pump is important, 28 - 30 inches mercury vacuum is good.

Of course it doesn't matter how it is achieved. But how you achieve it will determine how low you can ultimately get the pressure.

Also, of course, you won't see 30" of vacuum unless you are under sea level. At sea level, a perfect vacuum (0 microns) is 29.9" or so. 29" of vacuum looks great on your gauge, but it is insufficient to do the job.

Water boils at about 212F at sea level. At 28" vacuum, it boils at about 100F, so unless it is very hot out, 28" isn't enough (29" gets you to about 80F). The purpose of using a vacuum pump is to remove water. Using a pump which will not develop sufficient vacuum is as bad as using any other defective tool.

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