A/C system evacuation - PeachParts Mercedes-Benz Forum

pmizell · #1 03-06-2004, 12:47 PM

The leak in my R-12 system was found to be at the expansion valve. I'll be replacing it soon, along with the receiver/drier and hopefully restoring my A/C system to like-new.

After replacing those components, I'm going to completely flush the hoses/evap/condenser and remove/refill oil in compressor and close the system back up.

At this point, from what I understand, I need to pull the system into a vacuum to remove any moisture prior to recharging.

I bought a "venturi-type" vacuum pump for this purpose, (Harbor Freight, hooks up to compressed air) and advertises a vacuum of 28.3" of mercury --- 4.2CFM consumed. <----not sure if that means pulled.

My question is: is this sufficient vacuum to properly remove any/all residual moisture in the system?

I really don't care to pay $150 for a 2-stage vacuum pump to only use once. Can these be rented somewhere?

Thanks for any insight you can provide!

engatwork · #2 03-06-2004, 02:12 PM

Quote:

is this sufficient vacuum to properly remove any/all residual moisture in the system?

no

Go to Autozone and they usually have a loaner. Put it on your cc and when you return it they will credit your cc. Pretty neat loaner program. They will not have any r12 supplies. You will have to find an a/c supply house for r12 materials. Don't let them try to sell you a kit. Oh yea, you can get the r12 oil from an a/c supply house too.

pmizell · #3 03-06-2004, 02:38 PM

Thanks Engatwork for the advice.

I have the R-12 (5, 12oz cans -- **original Cold Shot cans acknowledging Jackd's response below) and a manifold gauge already so I'm pretty much ready to break down the system.

I'm trying to determine how many O-rings I'll encounter and thus how many I'll need to replace. Looking on Fastlane is really no help. It looks like there are 4 that go on the exp valve alone, and 2 on the compressor suction and return lines and I'd imagine a couple more btw compressor and condensor.

Again, thanks for the help!

Jackd · #4 03-06-2004, 02:38 PM

Be careful where you buy your R-12.
Up to 80%/85% of all R-12 sold on market today is recycled R-12.
There are non-scrupulous (but inventive) recyclers going around scrap yards pulling out R-12 from old/scrapped cars and re-selling it it in nice clean bottles. You get all kind of contaminants (water, old oil, ) in that stuff.
Not very good for a freshly rebuilt system
JackD

#5 03-06-2004, 07:06 PM

It sounds like you have original cans, so it should be clean.

If you only have the one leak that you have identified, there is really nothing to gain by flushing and all that. Since you have a new f/d, then putting it on would be a good thing, but you have no reason to flush the system. Simply replace the expansion valve first, putting a little refrigerant oil or nylog on the o-rings, once that is tightened up, then replace the f/d last so that you get minimal moisture into it.

Then using a motorized vacuum pump, evacuate thoroughly, do a gross leak check by seeing that it will hold vacuum for about five minutes then evacuate a little longer. If it is warm weather, you should be able to adequately evacuate in a few hours. If it is cold it will take much longer to boil out the moisture.

The only time you need to thoroughly flush is if you have blown a compressor that scatters debris through the system or if you are converting to a different refrigerant meaning that you must get all the old oil out.

Good luck,

brewtoo · #6 03-06-2004, 08:29 PM

"I really don't care to pay $150 for a 2-stage vacuum pump to only use once."

Where can I get one of these for $150?

BTW, the Harbor Freight pump-ette won't cut it for this.

#7 03-07-2004, 07:59 AM

Follow Jims advice & get one at Autozone.

My $0.02,

pmizell · #8 03-07-2004, 11:48 AM

Thanks LB for the advice

The R-12 I bought on Ebay is original cans -- they appear to have been stored away, so that's nice to know I'll have virgin freon in the system.

I added Freeze-12 last summer as a top-off, so I'll need to do the full flush.

I had no clue that Autozone rented pumps, so I'll definitely take advantage of that.

Brewtoo: if you do a search on Ebay for "Robinair" or "Yellow Jacket" you'll find some good used vacuum pumps, anywhere from 1.5CFM to 6.

Good Luck and thanks again!

samiam4 · #9 03-07-2004, 11:24 PM

If your looking for o-rings- call FASTLANE and ask for all the mating o-rings.

I've never had a problem getting the right ones.

Thanks on the Autozone tip for the vacuum pump!! I looked and found the small 1/3? 1/6 hp pump for $159 new.

I would avoid the venture pumps as they do not pull down as low.

Michael