DIY'er needs method to evacuate 134a from ac system

All,
Is there a way to build/connect the following items to an AC system and have it evacuate all of the refrigerant.
1. Manifold gauge set 2. 2cfm 2-stage vacuum pump 110v
3. emty propane tank.
My understangin is that the commercial units costing $4,000 essentially are built fromthe same components. I have no plans to reuse the old 134a. All I want to do is depressurize the system so that I can replace a bad compressor.
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BoBo wrote:

If the compressor's shot, there probably isn't that much refrigerant left in the system to worry about.
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Sounds like it would be cheaper (and easier) to purchase a compressor, and take it to a certified shop to have it replaced and your system vacuumed and recharged. I had a Ford done recently for $120.
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I have the manifold gauge. I bought it on Ebay for $25 I'll cost $30 to rent the pump for the weekend. The propane tank was free. 2 cans of R-134a is about $12 I can purchase a brand new GM HT6 compressor for $220
Total: $287
I've called some ac shops and dealers and they want between $600 - $1100 to do the job
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If you have any refrigerant left, you can pump it out of the system into an approved tank (but I am not sure the propane tank would fit that requirement). You can even chill the tank with something like dry ice to make the job easier. What do you intend to do with it then??
GM compressors often fail at the front seal and the refrigerant is mostly lost anyway. Do you know if yours has a significant charge?
The sealed system may have a lot of contamination in it. Do you intend to flush it and replace the expansion device (orifice tube or expansion valve)?
I have to do this job soon on my van to replace the evaporator core. I might have a little refrigerant pressure left, but have no intention to try to recoup the couple of grams of refrigerant. It will be just traces.
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It does take some expertize to do the job right/safely. Not knowing what the gauges are 'telling' you can lead to a dangerous situation and damage the ac system. None of it is rocket-surgery though and is easy enough to learn.
As to evacuating the system: I'd suspect that was done already by the compressor when it gave up. The gauges will tell you that. A vacuum pump might be a good investment in the 'long run'
Those evacuating systems not only capture the refrigerant but also clean/recycle it for reuse.
Dave S(Texas)
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On Thu, 17 May 2007 08:26:53 -0500, snipped-for-privacy@webtv.net wrote:

I have the factory service manual for the truck that explains in detail how to diagnose and repair the ac system. As long as I keep an eye on the gauges and I don't open the high side while recharging, it's pretty safe and starightforward procedure.
The manifold is in the process of being shipped so I don't know what the pressures are. Assuming both high/low sides read zero, what is the possibility of liquid refrigerant still remaining? If there is a leak, will all of the liquid refrigerant boil off in a matter of a few seconds once the atmosphere enters the system?
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The same as your gauges read, zero.

Depends on the size of the leak, but once you open the system (like disconnecting line sets), the liquid will boil off almost instantly.
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detail how to

The whole system must be flushed. This procedure can not be side-stepped. De-natured alcohol pushed through the lines under pressure will do the job. Compressors are not a piece you want to replace often. The orifice tube must be replaced and the accumulator should also be replaced. Follow the procedures for adding oil into the system. Check every connection for signs of leaking. While the system is 'down', I'd replace the O-rings at all connections. Doing the job right will be rewarded with a trouble-free AC system for years to come.
Dave S(Texas)
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BoBo wrote:

That is because compressor failure usually means you have a LOT more to do than just replace the compressor.
To start with you need to evacuate the system. Then pull the compressor and the lines to the condenser to see how much crud from the failed compressor made it into the condenser. Then you need to flush the condenser (IF it can be flushed,some cannot) Then you replace the accumulator/drier because of the crud from the compressor and the orifice tube is probably plugged as well. That gets you back around to the evaporator which will need to be flushed at least. Now that the system has been flushed and the plugged parts are replaced you can reassemble the system (add the proper amount of oil to the compressor & add an inline filter just in case you missed some crud) and vacuum it down and see if it holds. Then recharge the system.
THAT is what the AC shops will do. If you JUST replace the compressor on a failed system you may as well take the money your spending on the parts and tool rental and burn it. Why? Very simply the new compressor WILL suck in debris from the failed unit which will destroy it in short order.
--
Steve W.
Near Cooperstown, New York
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wrote:

The compressor didn't have a massive failure. Only the seals are leaking. Nevertheless, I will blow out the system wth compressed air before recharging, replace the orafice tube and accumulator.
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As I suggested in my previous post, and in total agreement with Steve W., you may well need to flush the system even if you have not had a major failure.
I just did my Reatta and upgraded it to R134a. It did not have a major failure, just an R12 leak at the front seal. It was not even a big leak.
We did the job correctly. We replaced the compressor AFTER removing the expansion device and filter/drier and flushing. It was full of black corruption.
There is a right way and a wrong way. You may get away with doing a halfway job....for a while.
Even doing it the right way should not cost $1100.
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