Hello all. I have an issue trying to revive the original R12 A/C system on my 83 Camaro. I have been scanning the forums, found lots of helpful information, but have not found information that quite fits my situation.

Background: This car has been in the family since new. I know what has (not) been done to it mechanically. The A/C system gradually "died" some years ago. Suspect leaky valves. While A/C was inoperable, the system has remained closed. Anyway...

In attempt to revive the system, the following has recently been done.

1. new schrader valves (green rubber).
2. reman AC-Delco R-4 compressor (rated ok for R12 and R134)
3. everything else original.
4. system was not flushed, and original oil (mineral I presume) remains in the system.

System was subjected to a (quality) vacuum pump, on both the high and low sides, for a few hours to evacuate any moisture. Also, verified the system could hold a vacuum (-30psi) overnight.
I acquired a case of R12 refrigerant NOS in 12 oz cans.
With a proper high / low pressure manifold gauge set, I started injecting refrigerant into the low side.
The first can filled while the system was under vacuum to help draw in the refrigerant.
Once the can emptied. I turned on/warmed up the engine, switched on max A/C
I observed the compressor switching on for a couple seconds (low side at 47 PSI), then switch off for a couple seconds (low side at 25 psi).
Since only one can, clearly not enough refrigerant, so this behavior is expected (as is verified by numerous other threads on this topic).
I added a second can,
I added a third,
I added a fourth
With each can, the time between on/off cycles increased, but NOT the time the compressor remained ON.
As for gauge pressures observed, the compressor switched ON when pressure hit about 47 PSI, and switched OFF when pressure hit about 25 PSI. So research says this is the pressure switch controlling the compressor.
Once the compressor switched off, the "ramp up time" towards 47 PSI (and compressor switches on) grew longer and longer with each can. But "compressor time" was always a quick couple seconds with the high side, hence high side pressure never exceeded much beyond 100psi
No cooling can be felt from the the vent system

Now, here is the issue. It *seems* I should be close to system capacity at 48 oz of refrigerant (?). But, I *know* higher PSI must be achieved on the high side for things to start 'cooling' (!).

Given the last three cans, observation suggests if I add one more can, the time between 'compressions' will get longer, but not the actual 'compression time'. Ram-up from MIN to MAX LOW Pressure will become longer. Actual compression time will remain short. Thus never attaining proper pressure on the high side.

After scanning the forums and studying the GM service manual, I am tempted to conclude "clogged/restricted orifice"???

I mean, with a properly working system, how long would you expected the compressor to remain engaged say on a 75deg F low humidity day?

Thanks for any insights that can be offered!
-robert

 

I'm not an HVAC expert but I'm decent with my own stuff.
a couple of things jump out at me.
Im not sure on the high side restriction as you would see a much higher than 100 psi.
For what it's worth here is my suggestions
question- did the old compressor fail or was it just replaced because of age ? If it failed you have no choice but to flush the entire system.
Find someplace that can recover your R12 as it's near impossible to find now.
Replace the office (they are cheap)
Replace the hoses as they age the freon will leak out the rubber.
Replace the receiver dryer!!!!
If you have access to a bottle of nitrogen purge the system. And do a pressure test with about 150 psi.
You can replace the mineral oil with ester oil that is compatible with both R12 & R134a.
On a 75deg day the compressor should run all the time till the evaporator coil gets down to about 35-40 degrees

 

4 cans is more than enough. The system is now overfilled.

ANY TIME you bust open an AC system for ANY reason, you should:

1. Strip all broken parts, and all rubber and sealing parts
2. Make sure the cooling system is working properly, especially the radiator fan
3. Flush ALL metal parts of the system you intend to re-use (evap, cond, metal lines)
4. Replace the compressor; fill to about half the system's oil capacity, through the suction port
5. Replace the orifice tube
6. Replace the accumulator/dryer; fill with the other half of the system's oil capacity
7. Replace all the O-rings
8. Replace all the old rubber lines with new "barrier" hose (essentially, polyethylene tubing covered with rubber)
9. Install all parts
10. Pull a vacuum; leave the pump running for at least an hour; verify that it holds vacuum below 29" Hg for at least a half hour

THEN AND ONLY THEN, recharge.

If you do not do this, then what will inevitably happen is, next week some one of those other old wore-out obsolete 30-yr-old dried up crusty things, will FAIL, and you'll be RIGHT BACK where you are now. AC is alot like automatic transmissions; you don't "repair" them, you RENEW THEM COMPLETELY so that they once again can live out their normal service life of however many years miles or whatever that is.

It's too late to go back into the past and undo and redo what should nave been done already. But that's about the only choice you have now.

DO NOT vent that R-12 to the atmosphere!!!!!!! It is VALUABLE. Go somewhere and have it recovered. If you redo the system correctly, you can re-use it. Or, you can sell it and buy R-134A, which is what should have been done in the first place. Not least because, you can actually still buy more if you need it, at least for the time being. But you have to make that choice BEFORE buying the OT and oil, because those things will be different for a 134 system, from what you'd use for 12.

You can't pull a 30 psi vacuum on Earth. Atmospheric pressure is only about 15 psi, and since a vacuum is 0 psi, that means that the most it can be is -15 psi compared to atmospheric. Sea-level atmospheric is 30 inches of mercury, which is what the "30" on the vacuum gauge means. It's not something you did wrong, but it's important to get the terminology right, just like in any worthwhile endeavor.

Compressor cycle time will depend on engine RPM, car speed, cooling system (fan) condition, ambient temp, ambient humidity, sunlight, blower motor speed, and various other factors. At 75 degrees in central Michigan in July, it should run pretty much continuously at idle. It might cycle a little at highway speed but probably not.

It would be instructive to know what the high side pressure is. At 75 degrees, sitting still, engine RPM 1500, fan properly working, in sunlight, function on Max, you should have somewhere around 35 psi on the low side and 250 - 275 on the high, with the correct charge. If it's cycling, the OT is almost certainly blocked by debris from the previous compressor, and the high side probably goes to 350 or more at the same time the low goes below 30.

 

I mean...... *technically* it's never "too late" to go back into the past - assuming you have enough Plutonium or you're Mr. Fusion is fully charged.

GD

 

Four cans at 12 oz each, is 48 oz.
The most 'official' looking data sources says that is about right.

1989-1992 All Engines R12 36.00oz Mineral 8.00
1985-1987 All Engines R12 48.00oz Mineral 8.00

Mines is an 83 so I suspect at least the same as 1985-1987

<peripheral info deleted thanks>


Now we are getting some where. The short compressor duration is the same, whether at idle or at highway speed.

The high side never really broke 110psi during compression. That is the mysterious part.

Thanks, yeah, that is my suspicion. Blocked orifice tube. As for 'compressor debris', there was never any evidence that it had failed. The choice to replace it was made because of it's age.

Looking back, after further research, it seems replacing the condenser would also be a good idea. It seems there are newer more efficient parallel tube condensers that will fit the F-body cars.

 

Well, this thread is aging, but I just followed liquid Blue's thread on R12 - 134a conversion - to use as a guide on how to clean parts and re-use, taking into account -- someone before me. who had converted to to R134 from R12 and replaced the compressor -- and I was just wanting to re-seal the leaks and check that the conversion was done well, with a complete flush of the system. The air con used to work, but never got very cold and the system has not worked for a few years do to leaks. Well, got it all done, kept the replacement compressor, and noticed the label on it said it was PAG oil filled when it was replaced, so I used AC delco pag oil referred to on liquid blue's thread. I used the RED orifice tube that he used, and besides those two things re-used everything else that is still in good condition. It appears (from the dye that leaked) that the leaks were probably just schrader valves, condenser in good shape, evap in good shape, so I flushed and put back. Anyway, recharged today, and I have the SAME EXACT SYMPTOMS as WESTSAIL42. 3 cans 12 oz loaded, and the compressor kicks on for 3 seconds, then off, then on then off, High side never gets much above 120 and low side bobbles 40 and 60. I have no idea what cycle switch is on there but the air con used to work 7 years ago. Tonight I ordered the Four Seasons one -- recommended on the other thread just in case it's that. All the components were flushed and flown out with high pressure, except compressor, which seems to work well when it is kicked on. Not sure what else to do besides replace cycle compressor switch.