How to "vac" AC down "from home"?

INFO:I have a 97, a few years ago my evaporator started leaking REALLY slow. So I put some stop leak in it and then it would hold for 2 months or so. Well for the last year my compressor has been going out.... grinding really loud and pulling volt gauge down to around 8 amps when I turn AC on.

SOOOO, I decided to buy a used compressor and put it in, but my mechanic is saying the stop leak goop will ruin his $10,000 vac machine. He also tells me after I "open" the system by putting new compressor on, it won't take the AC from a can because there is no vac.

QUESTION: Can I vac my system down from home? Do I need to add anything else to system to make sure I don't ruin my new compressor?

Thanks guys, I know alot of things about jeeps, but NOTHING about how an AC system works.

well...first off there is never a vacuum in the a/c system, unless you have something plugged. you should evacuate the system after you open it up, but if you just hook up a can to the low side, (larger pipe) the freon should go in even if the system is empty. the low side pressure when operating proper will be in the 30-40 psi range which is well below the pressure in a 1lb can of 134a. if it does not seem to take it you may have to short the low pressure switch to kick on the compressor.

Red97XJ said:

INFO:I have a 97, a few years ago my evaporator started leaking REALLY slow. So I put some stop leak in it and then it would hold for 2 months or so. Well for the last year my compressor has been going out.... grinding really loud and pulling volt gauge down to around 8 amps when I turn AC on.

SOOOO, I decided to buy a used compressor and put it in, but my mechanic is saying the stop leak goop will ruin his $10,000 vac machine. He also tells me after I "open" the system by putting new compressor on, it won't take the AC from a can because there is no vac.

QUESTION: Can I vac my system down from home? Do I need to add anything else to system to make sure I don't ruin my new compressor?

Thanks guys, I know alot of things about jeeps, but NOTHING about how an AC system works.

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Yes, but you'll need a vacuum pump to pull a hard vacuum.

Also, if you've got stop leak in there, but you've fixed the leak (new compressor,) you may want to have the system flushed out before you vac & refill. I never have liked stop leak stuff - it usually ends up causing more trouble than you originally had.

Call around and see if you can't rent a vacuum pump. If your worried about the goop, squirt a little compressor oil into the pump inlet and put a filter in line between your system and the pump. Ask the refrigeration guy if he has a used filter dryer around, you just need to filter the freon some before it gets to the vacuum pump.
You can use the compressor to get a vacuum, though it takes some thought and familiarity with the valves, gages and electrical. Not the type of thing I'd recommend for a novice. You can actually recover most of the freon if your good, using the AC compressor. A compressor vacuum isn't as good as a vacuum pump vacuum, because it takes a while with a constant vacuum to get all of the freon, air and moisture out of the oil (and the rest of the system). A compressor vacuum is a short term vacuum and has to be repeated many times to be thorough. Chances are you'll eventually spray compressor oil all over the place.
You need the vacuum to get the air out and boil the moisture out of the system. A vacuum does help with the refill, but it's not absolutely necessary. Heating the cans in hot water, being careful to keep the valve away from the water, will force most of the gas out of the cans.
A fill by freon weight is always the best.

Like 5-90 said, flushing the system may be necessary, the expansion valve orifice can get gummed up, the valves may not seat right. Good luck in finding an environmental flushing agent. You can't get liquid freon anymore, carbon tetrachloride is hard to come by. Somebody mentioned brake cleaner, sounds reasonable, but I've never treid it myself.

VERY cheap vacuum pumps from Harbor Freight:

P/N 92475-3VGA $10.00
P/N 96677-0VGA $20.00

neither would be good for frequent use, but as a one or two time repair, I'd give them a shot!

You can use a compressor out of an old refrigerator to pull a vacuum.

I used the Harbor Freight air-powered ejector vacuum pump on mine after I changed the condensor. It pulled 26 inches Hg vacuum which meets the factory spec for evacuation. Don't forget to add oil according to the FSM. There's a set amount of oil for each component you replace. Also, make sure you use the correct oil too.

so, will it work if I just put a used compressor in and then just add freon with oil in it?

I can get the compressor for under $100.

NO. You need to evacuate the system before adding coolant.

old_man said:

NO. You need to evacuate the system before adding coolant.

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OK, then what? I will buy a harbor freight vac.

I hate to poo on everybodys cheerios this morning, but have you checked your local or State laws regarding you working on your own AC system?

A number of States manadated, under a fairly stiff financial penalty, that a person licensed by that State only be the one capable of working on these systems.
If you have a buddy that is so licensed, it may not be a bad idea to have him over for a beer to "supervise" the activity.

Other than that, the technical aspects are not too bad, and are in FSM.

Pump down the system to eliminate any air/moisture in the system which will contaminate the Freon, add oil, and fill (Which requires the use of a set of differental guages to monitor the high and low pressure sides of the system).

Ron

RED97XJ, the basics are easy to state, but require a lot more knowledge to implement. If you really want to maintain your own system, I suggest you obtain a manual on basic refrigeration. You need to understand the problems associated with contamination, and exactly what your trying to accomplish. I doubt following the instructions given in this thread will give you satisfactory results. There's more to it than "just vacuuming down the system" and attaching a can of freon to refill.
Books like "Refrigeration for Pleasure Boats (Nigel Calder), and Haynes Techbook "Automotive Heating & Air Conditioning" need to be read and understood before you embark on major A/C repairs.

xjbubba said:

RED97XJ, the basics are easy to state, but require a lot more knowledge to implement. If you really want to maintain your own system, I suggest you obtain a manual on basic refrigeration. You need to understand the problems associated with contamination, and exactly what your trying to accomplish. I doubt following the instructions given in this thread will give you satisfactory results. There's more to it than "just vacuuming down the system" and attaching a can of freon to refill.
Books like "Refrigeration for Pleasure Boats (Nigel Calder), and Haynes Techbook "Automotive Heating & Air Conditioning" need to be read and understood before you embark on major A/C repairs.

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One reason I'm hesitant to give A/C advice, it can go wrong quick. Darned auto A/C systems are really inefficient, they go from one end of the envelope (low) to the other end of the envelope (high) in seconds. You've got four valves, two gages, in system high and low pressure shutoff switches and a few pressurized gas sources (with different pressures) all going on at once (and constantly changing).
You have to be quick on the gage valves or your pumping freon back into your freon can. Static fill equipment is expensive.
And in the process your trying to find the happy middle on the pressure gages, trying not to over fill the system and not really knowing if it will work tomorrow when the thermometer hits a 110F.
The only way to do them and have much hope of success is luck, or recover the gas, vacuum them down and refill by the weight of the freon. If your using small cans it's doable, if you leave a few ounces in every can, your guessing. A good scale to measure the freon weight is expensive, you really need a scale finer than an ounce.
The reason so many guys are trying to do this at home, is because they've legislated the service techs. into charging doctors fees, the techs. have to charge an arm and a leg to pay for there equipment (and licenses).

We really need a tech article on this, step by step, maybe even alternative methods, depending on the availability of the proper equipment. With the appropriate disclaimers.
aperwork

great news, I realized I am in over my head, so I am buying the used compressor and a harbor freight vac, and my mechanic is going to do it for me!! Mabye not the cheapest, but it will work!

Red97XJ said:

great news, I realized I am in over my head, so I am buying the used compressor and a harbor freight vac, and my mechanic is going to do it for me!! Mabye not the cheapest, but it will work!

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Still gonna be cheaper than a stealership fix !!! :thumbup:

Be nice if you would post the results after it's all said and done.

Red97XJ said:

great news, I realized I am in over my head, so I am buying the used compressor and a harbor freight vac, and my mechanic is going to do it for me!! Mabye not the cheapest, but it will work!

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That really is the way to go. You save a bit on parts, and you get to learn with out the outcome of the project being completely in your hands. You should learn alot!

Good Luck!