AC repair Silly Question - PeachParts Mercedes-Benz Forum

maina · #1 06-01-2006, 11:53 PM

I am about to tackle repqairing my AC my self on my 83 300SD and feel pretty confident except for one last part. After I re-install the compressor, drier, and expansion valve with new o-rings and ester oil, where do I connect my vacuum pump to dry out the entire system? I found a cheap vacuum pump at Harbor Freight (http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=92475) and thought it would be better than no vacuum at all prior to filling with 134. They mention hooking the vacuum fitting to the car's "drain port". What is this drain port? Also they have a fitting on the vacuum but no tube or quick connect to the car. Do they mean hook the vaccum to the drier, 134 high side fitting, low side fitting? Ahhh... I guess I am just a little "green" here!

romansek · #2 06-02-2006, 01:03 AM

Vacuuming the system is a must for proper operation of AC. Connect the vacuum pump to the system through the charging port by using the gauges or charging hose. Before charging the system be sure that the system holds vacuum. Good luck.

maina · #3 06-02-2006, 01:09 AM

There is only one nipple coming of the vacuum. do I connect to the high or low side fitting?

Motorhead · #4 06-02-2006, 01:24 AM

If you have a gauge manifold set, hook the vacuum pump to the center or yellow hose. Hook the low side hose, blue, to the low side. hook the high side hose, red, to the high side. OPEN BOTH valves a turn or two and start the vacuum pump.
When done evacuating, CLOSE BOTH VALVES FIRST before stopping the vacuum pump.
You charge through the LOW SIDE ONLY. you hook your refrigerant source now to the yellow line and use the low side manifold valve to ADD refrigerant. This allows you to "fine tune " the amount that you put in while checking your pressures.
Look under the hood, generally on the radiator support and It will tell you how many pounds your particular car takes.
Chris

romansek · #5 06-02-2006, 01:26 AM

The charging port is low side.

pdrayton · #6 06-02-2006, 07:44 AM

bit late now maybe, but have you considered using R12?

I just did a redo of my 83 240D - new compressor, drier and flushed, with R12.

From everything I read, and the advice of a long time ex merc mech, R12 is the way to go. The 123s don't have a big enough radiator to cool effectively with R134. PLus R134 has higher pressure. Basically, it sucks. There are lots of posts on it, here and on other sites.

If you're set on R134, and you're doing it all yourself, consider Freeze 12 - it's basically 50% R134 and 50% R22 (I think), anyway, it cools better and is pretty much regular. Just don' expect a auto shop to like you if you bring it in for service - they probably won't have the equipment to officially deal with it.

Also, for vacuum, I vacuumed my setup with a compressor I took out of an old fridge from a junkyard. Cost = $0. Vacuumed to 26 " HG and then let it sit to check the vacuum held.

I wouldn't trust a harbor freight pump to do too well myself.....Some of their tools are OK, some suck. I was going to use that same air operated vac pump - actually, I bought one, but took it back after I read about what a pounding it puts your air compressor through.

You can buy R12 on ebay for about the same price (maybe a littel more) as R134. I believe you need 2.2 pounds for the 300D - less than 3 cans.

That's my 2c. If you have any questions, let me know.

signalredcoupe · #7 06-02-2006, 09:09 AM

I wouldn't trust a harbor freight pump to do too well myself.....Some of their tools are OK, some suck. I was going to use that same air operated vac pump - actually, I bought one, but took it back after I read about what a pounding it puts your air compressor through.

I bought the same venturi vac pump from Harbor Freight. Yes, their tools are cheap. Some are good for certain applications. The pump worked great although I didn't keep it on too long to save my compressor, but it pulled a good enough vacuum to yield approx. 35 degrees F from the duct here in central Florida. Paul.

pdrayton · #8 06-02-2006, 09:17 AM

The point of pulling the vacuum is to get all the moisture out of the system. at 27" HG, water boils at room temperature (or near enough). Pulling the vacuum has to be done for long enough to allow all the moisture to boil and be extracted. That's why you need to keep the vac on it for at least 15 minutes.

That way your A/c investment is protected.

35 deg F at what ambient temperatur? I'm in Fl too, and getting about 50 deg when outside is 90. Thats' with the windows open so I can test direct cooling, not looped cooling if you know what I mean.

dannym · #9 06-02-2006, 10:05 AM

Quote:

Originally Posted by pdrayton

The point of pulling the vacuum is to get all the moisture out of the system. at 27" HG, water boils at room temperature (or near enough). Pulling the vacuum has to be done for long enough to allow all the moisture to boil and be extracted. That's why you need to keep the vac on it for at least 15 minutes.

That way your A/c investment is protected.

35 deg F at what ambient temperatur? I'm in Fl too, and getting about 50 deg when outside is 90. Thats' with the windows open so I can test direct cooling, not looped cooling if you know what I mean.

15 minutes is not long enough. you would need a 100+ micron pump to get the moisture out that fast. 1 hour is considered the least amount of time. With that venturi pump I would say let it run all night.

Also did you flush the system?
How much oil are you adding?
have you ever heard of Nylog?
If not then you should do a seacrh and read some of the AC threads in the archives.

Danny

leathermang · #10 06-02-2006, 11:43 AM

Listen to Dannym .
A lot of people have posted a WEALTH of information , including WARNINGS, in our archives. I have pretty much given up trying to help because Diesel Giant is allowed to post trash concerning Freeze12, which he SELLS....he says things which all sorts of trustworthy references show not be true... yet it is allowed to stay in the posts for unsuspecting persons to follow. --Greg

signalredcoupe · #11 06-03-2006, 08:25 AM

Quote:

Originally Posted by pdrayton

The point of pulling the vacuum is to get all the moisture out of the system. at 27" HG, water boils at room temperature (or near enough). Pulling the vacuum has to be done for long enough to allow all the moisture to boil and be extracted. That's why you need to keep the vac on it for at least 15 minutes.

That way your A/c investment is protected.

35 deg F at what ambient temperatur? I'm in Fl too, and getting about 50 deg when outside is 90. Thats' with the windows open so I can test direct cooling, not looped cooling if you know what I mean.

I got approx. 35 degress F with recirculated air of course. Fresh air about 5 degress higher. All cars are different. When I had my 240D, I used to get 38 degress running on the interstate in recirc.-a sedan with no window tinting in 95 degree weather. This is of course with R-12 & a stick thermometer in the center duct-the best possible conditions. Paul.

buch32 · #12 06-03-2006, 11:43 AM

[QUOTE=maina]I am about to tackle repqairing my AC my self on my 83 300SD and feel pretty confident except for one last part. After I re-install the compressor, drier, and expansion valve with new o-rings and ester oil, where do I connect my vacuum pump to dry out the entire system? I found a cheap vacuum pump at Harbor Freight (http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=92475) and thought it would be better than no vacuum at all prior to filling with 134. They mention hooking the vacuum fitting to the car's "drain port". What is this drain port? Also they have a fitting on the vacuum but no tube or quick connect to the car. Do they mean hook the vaccum to the drier, 134 high side fitting, low side fitting? Ahhh... I guess I am just a little "green" here![/QUOTE

I have used an Air-Vac (purchased from robinair? for years. Your compressor must be able to maintain 100psi for 1 too 2 hours. My compressor is 10HP and liquid cooled.

dmorrison · #13 06-03-2006, 07:38 PM

Quote:

Originally Posted by maina

I am about to tackle repqairing my AC my self on my 83 300SD and feel pretty confident except for one last part. After I re-install the compressor, drier, and expansion valve with new o-rings and ester oil, where do I connect my vacuum pump to dry out the entire system? I found a cheap vacuum pump at Harbor Freight (http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=92475) and thought it would be better than no vacuum at all prior to filling with 134. They mention hooking the vacuum fitting to the car's "drain port". What is this drain port? Also they have a fitting on the vacuum but no tube or quick connect to the car. Do they mean hook the vacuum to the drier, 134 high side fitting, low side fitting? Ahhh... I guess I am just a little "green" here!

Please don't take this wrong, but by your post above, there is way to much that you don't understand about the AC system in your car and working on an AC system in general.
So lets approach that first. Consider getting your 609 license. Its easy to do and will teach you everything you need to know (3 years ago I did not know enough about AC systems either). Go to a good book store and sit down with a coffee and read one of the Automotive AC books available. 30 minutes of reading will provide a wealth of information, and make sure everything is being covered. Once you do that, You will still have questions specific to Mercedes and we can answer those. Doing this will reduce your frustration and make the rebuild a bit cheaper. You won't be re doing the system in a little bit due to improper methods.

Dave

pdrayton · #14 06-04-2006, 08:55 PM

Buch32 - Dmorrison is right - read up on it - there's lots of info that's easy to get to.

Also, be careful hijacking other peoples posts - it might upset some. (Hijacking = posting your questions on someone elses post). Start your own post if you can't find the answers in the archives.

Paul