AC R12 re-charge -- how to?

[got2haul]

My in-dash aftermarket AC is no longer blowing cold air.  I don’t know much about AC systems, so I had originally planned to pay a local shop to convert my system to R134a and replace the compressor and all hoses under the hood for $800, which I talked about in an earlier thread. However, in a money-saving turn of events, a few days ago a friend gave me a half-full 30lb container of R12 Freon that he no longer needs.  So I bought a dual R12/R134a manifold, gauge, and hose set.  I’ve studied my 1980 service manual, but it was written for factory air systems, so I’m not sure how to translate the instructions on adding refrigerant to my system.  Another friend of mine added R12 for me a couple of years ago, but I guess I wasn’t paying too close attention, because I don’t remember where he attached the lines.  Picture 1: the dryer or accumulator canister (not sure what it’s called) has a hose connected to it that goes through the firewall to the unit under the dash.  On the other side of the unit, the hose goes to the condenser in front of the radiator.  There is a sight glass on top of this unit.   Picture 2: on the back side of the compressor are two threaded connections that look like they correspond to each of the two hoses connected to it.  One of these hoses also goes through the firewall.  Where do I connect the R12 fill line?

[VileZambonie]

the low side fitting for R-12 should be physically larger than the high side port (opposite of R134a). Attach your manifold gauge set and hook the center hose to your R-12 source tank. Start the engine and turn the AC on. Through the LOW side open the source tank valve and open the low side manifold valve. (do not open the high side!) Add a little at a time until you get the desired pressures. I'll post a pic of a good pressure chart for you.

[VileZambonie]

[got2haul]

the low side fitting for R-12 should be physically larger than the high side port (opposite of R134a). Attach your manifold gauge set and hook the center hose to your R-12 source tank. Start the engine and turn the AC on. Through the LOW side open the source tank valve and open the low side manifold valve. (do not open the high side!) Add a little at a time until you get the desired pressures. I'll post a pic of a good pressure chart for you.

Thanks for the chart!  I think that will be very helpful.  I'm still a little confused about where on the system to hook up the low-pressure hose.  Using the photos I provided, can you tell me if I hook the low side hose to the compressor fitting (at the hose that's going through the firewall)?  Is it the internal diameter of the fitting that is a different size, because it looks to me like both fittings on the at the back of the compressor are the same size (at least externally)?  I haven't received the manifold yet (purchased new online), so i can't determine the answer to that last question until they arrive.

Sorry if all this is elementary.  I just have no real experience in AC, and I'd like to do this soon so I can enjoy driving my truck this summer.

[VileZambonie]

If the only fittings are on the compressor then you have to use them. The low side goes towards the evaporator. The high side goes towards the condenser. The exterior fittings should be different sizes. Being aftermarket this may no be the case. So in your pic the lower fitting should be the low side.

[rustys82]

the condensor coil is infront of the radiator and the evaporator is inside you cab(in your situation). like vile said add thru the low side. so hook up you gauges and see which port is low and high while the engine is running. swap hoses if you hooked up wrong. your blue gauge is low and red is high. and like vile said add a little at a time and wait a couple minute in between to le pressures stabilize. you dont want to add too much.  but if you are leaking out the refrigerant(freon), it might not be worth adding all the time. R-12 is very expensive and almost imposible to find. in the long run it might be cheaper to convert.

[got2haul]

Thanks for that info.  I last filled the system over a year ago, so it is leaking, but very slowly.  I do plan to convert to R134a, but now that I have some R12 on hand, I'm going to wait until it's gone.  As soon as my manifold set arrives, I'll give adding some of the freon a try.  It'll be nice to have a cool cab once again.

[Skunksmash]

You can't buy R12 here in Texas cause its only sold to certified AC people.

[got2haul]

The 30lb container of freon I have has a label on it that says on one end of the container, "this end (up) for gas", and on the other end of the container 'this end for liquid".  So turning the container upside down will get you one or the other -- freon in liquid form or freon in gas form?  Which form do I use to fill the system, gas or liquid?  So how do both liquid AND gas states work in the same container, anyway?  Sorry if there is an obvious answer to this -- I never took chemistry.  Thanks.

Wanted to share this, too:  I found some interesting information on the EPA website:

http://www.epa.gov/ozone/title6/609/index.html

I found a chart on the site that shows the MVAC refrigerants fitting sizes and label colors:  For CFC-12 (freon), for pre-1987vehicles, the fittings on both the high and low side are the same size: 7/16-20.  For Post-1987 vehicles, the fitting sizes are different; High side is 6/16-24 and the low side is 7/16-20.

(http://www.epa.gov/ozone/snap/refrigerants/fittlist.html)

[VileZambonie]

You want gas. If you wanted to get certified to handle refrigerants it's an open book test for $15 bucks. Go to www.ase.com