A/C Vacuum, does this look good? - PeachParts Mercedes-Benz Forum

rbardolv · #1 05-26-2007, 06:15 PM

Hey guys,

I am under the impression that I must have a vacuum in the system before charging. I am starting off with a "just flushed" system, new oil in pump and new drier (7oz), new o-rings, new expansion valve. I have her in pieces now and will be assembling soon..

My question(s) are:

After I put the oil in and seal her all up, do I then apply a vacuum to the system to evacuate air / moisture? If so, does this look like a good device to do so:

http://cgi.ebay.com/Air-Conditioner-Air-Vacuum-Pump-Air-Vac-Gas-A-C-AirVac_W0QQitemZ110130632023QQihZ001QQcategoryZ22664QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

How much vacuum should be applied / how long should It be applied?
How much vacuum should I leave in the system?

Ps. I have a new mighty vac with gauge just sitting there..

Thanks gurus!

AdvisorGuy · #2 05-26-2007, 06:25 PM

You can't vacuum the system with a Mighty vac. You need an electric vacuum pump or an a/c recovery/recycling machine to do it. If the system is leak free, it should pull down to nearly 30 inches of vacuum in just a few minutes but should be vacuumed for 30 minutes minimum but 45 to 60 minutes is best. Vacuum pump shut down afterwards, the system should hold vacuum for at least 10 minutes. Then recharge.

As for that pump, as long as it can pull at least 25 in of vacuum, it should be ok. It's an air powered vacuum pump. I have a Snap-On similar to that.

Knightrider966 · #3 05-26-2007, 06:32 PM

Quote:

Originally Posted by rbardolv

Hey guys,

I am under the impression that I must have a vacuum in the system before charging. I am starting off with a "just flushed" system, new oil in pump and new drier (7oz), new o-rings, new expansion valve. I have her in pieces now and will be assembling soon..

My question(s) are:

After I put the oil in and seal her all up, do I then apply a vacuum to the system to evacuate air / moisture? If so, does this look like a good device to do so:

http://cgi.ebay.com/Air-Conditioner-Air-Vacuum-Pump-Air-Vac-Gas-A-C-AirVac_W0QQitemZ110130632023QQihZ001QQcategoryZ22664QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

How much vacuum should be applied / how long should It be applied?
How much vacuum should I leave in the system?

Ps. I have a new mighty vac with gauge just sitting there..

Thanks gurus!

I don't know enough about the device you showed, but it does not look like a vacuum pump. You need to pull a vacuum for least 25 to 30 minutes at 30 cubic inches of vacuum for complete moisture removal but a hour would be best. You can recharge your system without vacuuming it out, but your performance will not be as good. I live in a dry climate and got away without this step in Phoenix as I only vacuumed out my system for 20 minutes.

techguy512 · #4 05-26-2007, 07:05 PM

Quote:

Originally Posted by AdvisorGuy

As for that pump, as long as it can pull at least 25 in of vacuum

In my opinion, the air powered pumps are NFG. I used an electric pump from the AutoZone
tool loaner program. Pulled 29+ plus inches, verified it held overnight.

Knightrider966 · #5 05-26-2007, 07:25 PM

Quote:

Originally Posted by techguy512

In my opinion, the air powered pumps are NFG. I used an electric pump from the AutoZone
tool loaner program. Pulled 29+ plus inches, verified it held overnight.

Good point since air powered pumps will use more air than the typical compressor can put out!

rbardolv · #6 05-26-2007, 08:51 PM

So, does every Autozone have this A/C vacuum to rent?? Does it come with the line to connect to my fitting? I have simply never done it before, so I completely ignorant...

Oh yeah, do I need to put a vacuum on the low side and the high side?? I can't find any finttings on the high side at all.. (its all stock R-12 setup)

Thanks guys!

AdvisorGuy · #7 05-26-2007, 08:53 PM

Pull vacuum from high and low sides but charge only from the low side. The high side connection is in front of the condenser between the left headlight and the electric fan.

techguy512 · #8 05-26-2007, 11:15 PM

Quote:

Originally Posted by rbardolv

Does it come with the line to connect to my fitting?

You need a manifold gauge set to attach to the fittings. You'll need it anyway to charge after vacuum.

rbardolv · #9 05-26-2007, 11:34 PM

ahhhh.. OKay now I got it!

Thanks guys, I'll give it a shot. I called a few Autozones around here and the biggest store actually has the pump available..

Now I guess Im off to rent an air compressor, vacuum pump, and gauges .. yay!

(I just like doing things myself) haha! (well, and I don't feel like getting ripped off anymore)

Cheers!

Matt L · #10 05-26-2007, 11:50 PM

You don't need an air compressor to use a motor-driven vacuum pump. Also, I would recommend buying a gauge set.

rbardolv · #11 05-26-2007, 11:55 PM

YuP I know Matt, I just need the compressor to fully flush the system out before buttoning her up..

Cheers!

JimmyL · #12 05-27-2007, 12:07 AM

Sounds like you are all over it! I use the Autozone stuff all the time, I am just very bad about returning it before my credit card bill is due. I have to pay the extra a month, then catch back up on the next months bill.....
It never hurts to take some pics whilst doing the job also......

We like to see that stuff.....

rbardolv · #13 05-27-2007, 05:08 PM

Hey guys,,,

I got some PAG 150 oil from Autozone. Will that stuff work OK in my system? I have the bone stock, fully functional R-12 system.

And if the PAG is total crap as being too hydroscopic, then could I button her up , evac, and add the oil later through the tap type can deal..? (as Im sure there is oil in the compressor originally)

Thanks.

Kuhlrover · #14 05-27-2007, 06:58 PM

As I have been reading through this thread I can tell you are pretty clueless about doing A/C work. I admire your tenacity to attempt to do it yourself but you really should try reading an A/C repair manual before you screw up your A/C system or worse injure yourself.

If you have a bone stock R12 system then you need to use A/C mineral oil or POE oil. If you put PAG oil, which is meant for R134a, it will gum up your system. Even if you properly evacutated the system, there will still be some oil that collects in the lower parts of the system such as in the bottom of the condensor.

What type of refridgerant are you planning to install back into the system?

Yes, you should pull hard vacuum on the system if you have had the system open where air and moisture could have gotten into it. However, a vacuum is not required to suck the refridgerant into the system. At 70 degrees F, R12 will create a vapor pressure of 70 PSI. The initial vacuum of the system will draw in the refridgerant and gas will flow from the can into the system until the pressure equalizes. Turn on the A/C and as the compressor runs, it will create a low pressure on suction side ( the low pressure side) and draw the refridgerant into the system. If the compressor doesn't kick in, you can jumper across the low pressure switch and force the compressor to run. As long as you have placed the proper amount of oil in the system, you won't hurt the compressor doing this.

Mastercool makes a good A/C repair manual. You should get it.

Good Luck. Don't hurt yourself. Keep the kids inside.

TimK

rbardolv · #15 05-27-2007, 07:14 PM

Thanks... Yeah I am privy to the information you described.. Its just that these old MB's have these sensetive, (specific pre requisites), systems and I don't want to screw it up..

That being said, I can't find any places around here that carry these types of specific oils and such for my "old sensetive R-12 system"... Hence, the questions for PAG and such...

I will be using enviro-safe, an R-12 replacement / substitute. I guess I will simply order the oil from envirosafe which is supposed to be a great oil that is
Compatible with mineral, ester or pag oils... I tried purchasing some polymax2 from an online source but I think they are a fly by night operation and I must dispute for a refund... hohum...

Thanks again for all the help.....

Im off to get cleaned up as I just had enough of screwin around for 3 hrs getting that damn new expansion valve replaced... (what a PITA)

Cheers!