The vehicle is a 1988 bronco converted to 134 about 3years ago. It sat for about two years with no use and the refrigerant leaked out. The guage reads 10 on the low side and no reading on the high. I don't know if I should just add refrigerant or flush first. All components were less than a year old when the truck was parked. It had received a new compressor, condensor, drier, orfice tube, evaporator core and one of the hose lines. It blew cold before it was parked. I don't want to add the wrong mixture of oil and refrigerant so I would like to empty the system and start from scratch. I don't think I need to replace anything except what ever caused the leak, probably an o ring. If I go that route, I need to know how to be sure that all old oil and refrigerant is out and how much to add back into it. I would like to pull a vacuum on it but I am not sure if I drain it first or just connect the pump and let it work so I can see if it will hold the vacuum and locate any leaks.

 

If it worked fine before after R134 conversion and has been sealed since with no contamination, it should be fine. Just recharge it with R134 and use a vacuum to evacuate and leak check it. You'll only be out $15. The o-rings should be fine, because conversion kits come with ester oil, which is compatible with both R134 and with any residual mineral oil left from the R12. I changed all my O-rings when I replaced my compressor because I went with the PAG oil per the compressor rebuilders recommendation.

You could pull your orifice tube and make sure there's no black crud on it, which would indicate a shelled compressor, I think 88 will have the FS10 same as mine. Those are notorious for failing (even without any R134) and when any compressor fails, the the condenser becomes the debris field. The next thing downline from the condenser is the orifice tube, which has a screen to prevent any loose pieces from blocking the orifice tube completely, and shutting off the flow of refrigerant (and therefore lubricant) back to the compressor. I pulled my orifice tube and had the "black death" all over it, so I changed all the components. The orifice tube sits in the tube going in to the evaporator. Disconnect the liquid line coming from the condensor. You'll need a garter spring tool to undo the fitting, its like a fuel injection fitting. A needle nose plier will pull the orifice tube out, and it's only $3 anyway, so replace it with one making sure to install it cafing the right direction.

I used a Harbor Freight venturi vacuum and manifold guage set to evacuate the air from the system. You need a 1/4 NPT to 1/2 acme adapter, which NAPA carries to connect the vacuum pump to the yellow hose. Open the manifold valves, turn on your air compressor and watch the guage pull down to 25-29 inches of mercury. Close the valves and make sure it holds for an hour or so. Then make SURE your high side valve stays closed, disconnect the vacuum and connect a can tap to the yellow hose. Open the low side valve and the R134 will rush in.

Start the engine and place a fan in front of the condenser or hose it down. Turn the AC on high and add R134 until you have about 70% of the R12 charge. Then add one ounce at a time until you have the coldest output temp at your dash.

Heres a chart with the AC capacities that I found:

http://www.motor.com/PDFs/QLG2003_AC_capacities.pdf

If the link disappears I can e-mail it.

 

Thanks, you have been most helpful.