Vacuum A/C System

97 Caravan. Plan to replace compressor, drier and expansion valve.Was told to replace oil in compressor before installing but I dont know how much since this is a used compressor and no instructions. Also,after replacing mentioned items will pull vacuum on system for a couple of hours. Question is, when I put the vacuum on, does this suck out the oil I just put in the compressor? This is 1st time I have overhauled an a/c and hope to be able to complete since my wife drives this van and not at all happy driving in the heat. Any help greatly appreciated.

Refrigerant Oil: A/C systems carry oil through the system with the refrigerant to lubricate various parts such as the compressor. R-12 systems traditionally used mineral oil for this purpose, but this does not work well with R-134a. As a result, two new types of refrigerant oils emerged that are compatible with R-134a: PAG oil and POE (ester) oil. Many car manufacturers now use PAG oil in systems originally equipped with R-134a. Aftermarket companies, on the other hand, often choose ester oils for lubrication with R-134a because they tend to attract less moisture than PAG oils. This makes ester oils better suited for in-service situations. For best results, follow the exact instructions of the company supplying the retrofit kit for correct oil type and quantity.
Most AC compressors only hold at MAX 2-4 ounces of oil (around 100cc)...if you overfill with oil it creates massive overpressure and usually can destroy the compressor rather quickly...so if crack open and vacuum down the lines...you shouldnt need to add any oil..so getting those small cans from freon..DONT get the ones that have oil in them or you will kill the compressor

Oh and vacuuming the lines...all it does is create a lower pressure..and water at low pressure boils (how you can boil a cup of room temperature water in a vacuum bell)all its doing is "boiling" the water out..the longer you leave vacuumed the less "moisture" in the lines

Caution! - Always use separate refrigerant recovery, recycling and recharging
service equipment for R-12 and R-134a systems. If the same piece of
equipment is used for both R-12 and R-134a systems, residual traces
of refrigerant will contaminate and damage the equipment.
Service equipment includes recovery, recycling, recharging station,
vacum pump, manifold gauges, etc.

Caution! - Do Not Blow compressed air and nitrogen through the compressor or
expansion valve. Refrigerant circuits retrofitted to us R-134a must
not be rinsed with agent R11.

Replacement compressors are filled with nitrogen. If gas does not
escape when removing protective caps on suction and discharge ports,
assume leakage and do not install compressor.

When replacing damaged compressors, ensure existing mineral based
refrigerants oil is drained and replaced with PAG oil.

Always replace receiver drier if refrigerant circuit is left open.

Due to residual amounts of mineral based refrigerant oil in systems
retrofitted to use refrigerant R-134a, the newly installed PAG
refrigerant oil will discolor immediately after use. This is normal
and does not indicate a refrigerant related fault.
Hope that helps...I recommend having someone who knows on hand

http://www.carcare.org/Climate_Control/refrigerants_oil.shtml

Brian
AwPhuch

Thanks for all the info AwPhuch. I have flushed the compressor with new PAG oil and added about 3oz before installing. I put a new drier on and everything is hooked up. I bought a little air operated ac vacuum but it didnt come with much for instructions other than attach to the ac drain port. It also didnt come with a hose to attach to the drain port.1st, I dont know with is the drain port and what kind of hose and coupling to but. Since this is 134a system, is it supposed to attach to the low pressure port where I put freon in or the high pressure port which has a red cap on it?? Also, any ideas about the hose that would attach to the vacuum with has a threaded fitting?? Thanks for your help...

Bought hose to attach from vacuum to ac line and pulled vacuum.Recharged with freon and ac works fine. Thanks for help. Wife very pleased driving to work this morning and had a/c. Used freon with dye and no leaks were detected.

How much freon did you put in?

Did you have the dual gauge to measure the freon?

Brian
AwPhuch

I pulled vacuum then added almost 3 tins X 12oz. of freon with dye but no oil added.I figured I poured about 4oz PAG oil in compressor then added about 34oz. of freon 134a. I have the hose and adaptor that came in a kit that tells what the pressure is for low side which is now reading in the green area.I dont have the gauges that measure the pressures for low and high side.Also,I had always been told when adding freon to keep can upright and allow to recharge as a gas but the freon I bought said charge as liquid only so I turned can upside down and it charged quickly.When I done this the pressure for the low side was reading in the red about 150psi and compressor wouldnt come on but I checked fuse and had blown fuse for compressor clutch, replaced and compressor came on and after awhile the pressure came down in the green area.My wife says a/c blowing cold but she hears a hissing sound coming from under hood.I checked this and can not pin point where this is coming from since it only does this while compressor is running.Not sure if its the compressor or what??

Yah if the compressor aint running the low/high side is equalized and you will see 150PSI on both sides...once the compressor kicks on though the low side will drop. the high side is where you need to look, because if you have too much oil it can create too much head pressure which means way too much heat on the compressor

If you vacuumed it down and left the system running and charged it and its in the green you should be ok...however let the car idle for about 20 min w/ A/C on MAX and make sure it stays in the green..

Does the hissing stay on all the time, or does it go away
It could just be the freon in the line building up on the high side equalizing the system (like when the compressor in a window unit kicks on)

Sounds like you did a good job..just keep checking the freon, I dont think you can hear it leak unless its a massive hole..then it wont blow cold for long!

Brian
AwPhuch