Cal

iTrader: (1)

I removed the freon line from the condensor while replacing the radiator on the wife's T/A, now I need to recharge the system. Do I need to pull a vacuum on the system first then and add oil with the freon? If so, how much of a vacuum? I just got a nice A/C gauge set/manifold; will this tell me when I've pulled a high enough vacuum? Someone made a post a while back on how they used an old refrigerator pump to pull the vacuum, but the search function is giving me no love! TIA!

Cal

iTrader: (1)

OK I found the thread, it's here if anyone else would like to see it:https://ls1tech.com/threads/showflat...true#Post15382

I'm still interested in any comments on performing this operation, though. I'm wondering if a 12 volt portable air compressor could be used to pull the required vacuum?

mcflyz28

I prefer a vacuum pump and a micron gage, moisture and air are bad for any system

LOnSLO

iTrader: (15)

You need to pull a vacuum of at least 29 inches, turn off the vacuum pump, and make sure it holds for a few minutes. Then, refill with 134. You need to borrow a good vacuum pump for this.

Cal

iTrader: (1)

Where could I borrow or buy one? I've never seen one anywere.

Cal

iTrader: (1)

Right, it says in the shop manual moisture and air are bad for the system; but wouldn't any method of pulling a vacuum address this? I'm looking at how I could put a fitting on the input to my shop air compressor to use it as a vacuum pump; I have a vaccum gage. Shop manual says to pull 27-30 inchs of Hg. Do you think this would work?

LOnSLO

iTrader: (15)

That won't work. It takes a good vacuum pump to get down to 29 inches. You may be able to rent one at a tool rental place.

Cal

iTrader: (1)

OK thanks, knowing that I won't waste the time to figure out how to hook up to it.

rbartick

You only need to add oil if oil came out with the refrigerant when you opened the lines. When you normally empty a system you use a hose attached to a charge port and you measure the amount of oil that comes out with the freon. You do not want to add too much oil to the system.


You need to pull a vacuum of at least 28 inHg for at least 30 minutes to pull the moisture out of the system. After pulling a vacuum for 30 minutes close all gauges and make sure the system holds the vacuum for at least 10 minutes. If the system holds hook a Freon source to the middle manifold line, purge the line of air, and then start to charge the system. Do not overcharge the system.

rbartick

I use this vacuum pump:

http://www.harborfreight.com/cpi/cta...temnumber=3952

I got it on sale for $10

canadian z28

just go to the dealer or good shop and get them to pull vac. All you got to do is add the 134-a. Saves on the run around and headache if you did it right or not. What are your plans on the pump if you buy it after you pulled vacuum anyway?

canadian z28

Checked the price of 134-a at work and it is $13 a pound. That's Canadian of course. So, that is something like $5 American or cheaper?

rbartick

You cannot do this. If you disconnect your gauges while the system is under a vacuum you will lose the vacuum and suck air/moisture in through the port you disconnected from. It only takes an instant to lose the vacuum if you disconnect a manifold gauge/charge line/vaccum line.

The system should be charged immediately after the vacuum procedure is completed. The tech that pulls the vacuum should also do the charge.

Cal

iTrader: (1)

WOW you guys really get hosed for freon up there! I paid about $4 each for two 12 oz cans; that seemed to be the perfect amount for my '93 Fbody.

Cal

iTrader: (1)

Wow that's an amazing deal! Venturi type that pulls 28"Hg! If you had said something sooner I would have given it a try. I'm done now, but that's what I'm going to use next time!

Cal

iTrader: (1)

OK I just finished up this job and it's working like a champ, pumping out tons of freezing air! Many thanks to all that responded to this thread, knowledge is good!

The Details: I wound up building an adapter hose to connect the input of my shop compressor into my gage manifold. I was able to get 21"Hg this way, which is a little short of what I wanted, but the system is working well. Next time I'll get a real vacuum pump. It held the vacuum without any perceptible drop for 15 minutes, so I added 2ozs of PAK oil, two cans of R134a and ended up with 33 psi on the low side and 165 psi on the high side at an ambient of 80*F. The shop manual called out 25psi/178psi @ 85*F.