I picked up an air operated vacuum pump on e-bay pretty cheap.. They also have a complete pump and gauge kit pretty reasonable...I does take a pretty good air compressor to drive one though.

 

OK... Its spellt...Phosgene...

 

Dave7.3, this isn't the exact vacuum pump I got, but its the same basic tool (can't seem to find the website I got mine from).

http://cgi.ebay.com/ebaymotors/Centr...QQcmdZViewItem

You need a decent size compressor to power it, but since we have one in our shop, it was cheaper than getting the electric pump. I think it needs over 5 CFM.


Catfish101, I know that R12 and 134A are harder to burn than propane (a lot harder), but its still something to ponder, for me at least.

 

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I guess I am more comfortable with 134 and 12 because you need an existing fire to get it going and propane you just need a spark.

 

Ok, now I see how it works. Thanks David85. Hook this up to high or low pressure end? Also, I have seen the R134a refrigerant sold in small bottles. You mentioned that you use the pressure from the tank to charge the system. How would you charge it with the little bottles that I have seen it sold in? Rather pay a couple bucks for a bottle instead of $100 for a whole tank of it...

 

Napa sells a conversion kit that I have used on several different systems, and had good luck. The kit has one can of refrigerant oil three cans of R134 end that screw on the line ports and the hose to add the refrigerant. I have just added the oil first then the 134. I have been told that the R12 oil will just settle out in the system, and the 134 oil takes over. I have never had to change any parts of the system using this kit. It is recomended that you remove the R12 before adding the 134, but I usually just leave it in and add the oil and the 134. Hope this helps.

 

To pull the vacuum, it doesn't really matter which port you use, since you will do this with the system off, but chances are, the vacuum pump will have a connector for the low side.

To charge the system.

If you pull a vacuum, then there will be a big difference in pressure between the can of refrigerant and the AC system, so once you hook up the can and open the valve, it will force the stuff in. The thing to remember, is that like propane the refrigerant is in liquid form under pressure, so when you put the stuff in, turn the can upside down, that way, you use the pressure to force the liquid in. If you have an LPG powered truck, the same rules apply if you run it dry (execpt a BBQ bottle is now the "jerry" can).

It doesn't really matter the size of the container, since it still takes the same amount of pressure to keep the refrigerant liquified.

Once you put enough into the AC system, you will hear a click at the compressor cycling switch, once this happens, it will get more difficult to put more refrigerant in since the pressures are getting close to being equal.

At this point you need to start up the truck and turn on the AC. This will activate the compressor, which in turn will pull suction through the orifice tube, and bring the pressure at the low side back down so you can keep adding more refrigerant. Keep track of how much you put in, and have a garden hose handy to spray on the radiator to prevent overheating of the system while you charge it.