I am making the change over to the R134A freon in my '78. I will change the dryer and flush the entire system but need to know if the system needs to be in working order for the flushing agent to work. What kind of pressure reading on the gauges will I need to see for the AC to cool good? I've read there is some sort of cycling switch that needs to be adjusted, what is that all about? What other things should I be looking for while I'm doing this? I pulled the system down and it held vacuum for 10-15 minutes so I think everything is up to par.

need to know if the system needs to be in working order for the flushing agent to work

No, disconnect all your lines and flush through them, the condenser and evaporator core.

What kind of pressure reading on the gauges will I need to see for the AC to cool good? This really depends on ambient, (outside) temperature. You need to start a 134a charge of -20% of original R12 charge and no more than -10%. You will want the accumulator inlet and outlet tubes about the same temp. You will probably see gauge readings between 35-50psi on the low side and 225-325 on the high.

I've read there is some sort of cycling switch that needs to be adjusted, what is that all about?

Your 78 should have a themostatic switch, so pressure switch adjustment shouldn't concern you.

I pulled the system down and it held vacuum for 10-15 minutes so I think everything is up to par.


Pull a vacuum for at least 30 minutes and see if it will hold for at least another 30 minutes.

What other things should I be looking for while I'm doing this?


Replace your orifice tube.
Check your hoses.
Double check your fan clutch and make sure you have a fan shroud!
Make sure your cooling system is up to par.

Man, I did it now!!!!!! I broke off the orifice tube inside the evaporator. Somebody (not me this time), bent the tube it was in so when I tried to pull it out it broke off. How long is that thing? I can see a small tube in the middle, way down inside and also what's left of the assembly.
1). Any tricks on gettin' that thing out besides replacing the evap?
2). I found alot of sand-like crap in the screen when I tried to get it out, where the hell did all that come from?
3). What kind of flush should be used? If you are just trying to get out the old oil, will brake clean do the same job?
4). The old o-rings are harder than a weddin' peter, will Viton seals hold up to 134?
5). The sticker on the original compressor says it holds 10 oz. of oil. Will 8 oz. of ester work or do I need to put in 10 oz.?
6). What kind of test do I need to make on the fan clutch?

http://acsource.com/ProductImages/orifice/451-314.jpg

There is a tool available called a broken tube remover, but I have never had much luck with one... more pain then it's worth, it's basically a screw you're supposed to thread into the broken piece, but all I have ever been able to do with one is to make the problem worse.
Usually I use a small propane torch to heat the tube around the orifice just enough to melt the plastic and then blow through the opposite, (suction) side of the core with compressed air. Of course you have to be careful not to get the aluminum too hot as it is very thin and easily melts...also, be cafeful when blowing out the old tube as it will now be an air-borne wad of hot burning plastic!

You could also get an orifice tube repair kit, but these tend to leak at the compression fitting.

http://elcaminocentral.com/articles/ac/otuberepair.jpg

2). I found alot of sand-like crap in the screen when I tried to get it out, where the hell did all that come from?

Crapped out compresser and/or accumulator.

3). What kind of flush should be used? If you are just trying to get out the old oil, will brake clean do the same job?


Brake clean works in a pinch, just back it up with compressed air.

4). The old o-rings are harder than a weddin' peter, will Viton seals hold up to 134?

Just use orings you are certain are compatible.

5). The sticker on the original compressor says it holds 10 oz. of oil. Will 8 oz. of ester work or do I need to put in 10 oz.?


10ozs.

6). What kind of test do I need to make on the fan clutch?


With the engine hot and off, make sure it does not spin too freely, that is, reach down, (again, engine off) and spin it by hand, it should not spin more than a blade or two.

Thanks Robert. You've been a big help!!

Any time.

Alright, still one more question. I see all these recharge cans "with sealant!" Is this stuff like dumping Stop Leak in your radiator everytime you add some antifreeze? I'm not one for "mechanic-in-a-can" fixes.

I'm not one for "mechanic-in-a-can" fixes.


Neither am I...save your money and your system.

I had a helluva time getting this AC working. I started putting in the first can and the compressor clutch wouldn't kick in. I knew it worked because I saw it turning earlier. Goofed with it for quite awhile before I went home and got the old compressor to rob the coil. The old coil didn't get me anywhere either. I finally figured out the low pressure switch is actually the ground for the coil circuit. AGHHHHHHHH!!!!!!!!!!! Oh well, the switch seal was leaking oil anyway so I had to do something about it. There goes one can of freon. I switched the switch (Whuuuu?) and started over. You know, if you don't get the snapring that holds the switch back in the groove, that sucker really shoots out with a quickness when 60PSI is in the system?! There went another 1/2 a can. I finally got everything going but the clutch was slipping when I started putting in the freon. Found out that the clutch needs to be set to a gap of .022"-.057" so I did that and it still slipped.
1) Why is it slipping when it worked fine before?
2) I think I need another can because the low side is about 28 psi and the high side is 185 psi. It was 82 degrees here today.
I ran the AC on the way home and when I got here and opened the hood the clutch had turned pinkish-blue. It's obviously still slipping. I don't understand. I'm pretty sure they don't have to "burn in". I'm using a '73 compressor on my '78. Is that my problem?

Sounds like the compresser is trying to lock up.

You know, now that I think of it, I bet you are right. Before I took it off, I was having problems with the belt squeeling like Ned Beatty in Deliverance but thought it was just an adjustment problem. Damn, there went ALL the freon now!!!! Thanks bud, I appreciate all the help you've given me. This has been a good learning experience for me.

I finally got the AC working tonight! The first rebuilt compressor had a problem with the front seal not wanting to hold a vacuum. The second one worked fine, so far. It was only about 70 here today so I really couldn't tell how good the system was working. I put 48 oz. of 134 in and had pressures of 37 on the low side and 225 on the high side. I've tackled two things on my car that had intimidated me, the automatic transmission and the AC system, and so far both have worked even after I messed with them.