I am about to charge the A/C system in my 1972 LS5 that has not worked for years. I Recently purchased this car. The system is all original and looks like it has never been apart.
I changed the A/C control panel switch and the A/C control panel blower switch. Installed a new belt and the clutch is now engaging.
The system had no charge. I installed 150 lbs of nitrogen and it held that for two hours, so no leaks. How do i know if i need to add any 525 viscosity oil to the system?
Is there a way to tell if the system needs oil?

 

If the system hasn't been operating, and looks like it hasn't been opened up, it would probably be a good idea to clean out the old, and put in new.
Myself, I would get some a/c solvent flush and flush the system.
To flush the system, you'll need a pressure tank to inject the solvent, then blow it out with compressed air.
You can buy a kit that has the tank and solvent. Dis-connect the compressor and drier/ accumulator lines. Inject the solvent, let it sit for a little bit, then blow out the solvent and old oil.
You don't put it in the compressor or the drier/accumulator.
It flushes the lines, evaporator and condenser.
Drain the compressor oil into a graduated beaker and put however much you got out back in.
Rule of thumb, barring actual specified quantity of oil, is 1 oz for evaporator, 2 oz for condenser, and 2 more for the lines. This is a ballpark number.
If I remember correctly, you want mineral oil if you are keeping it R12. If you are changing to R134a, you will need pag oil, and to flush the system of old oil, as pag and mineral oil don't play well together.

Beautiful 72. I wanted a 72, but I found my 74, before a 72 came along.

Hope this helps.
Good luck.
Jeff

 

Hi Jeff, Thanks for the info. Sounds like a good plan to flush the system. How do i drain the compressor? Looks like it might have a small drain plug near the bottom.

Thanks Ron

 

Can't say for 100 percent certainty, but I believe the plug you are referring to, is the drain plug.
pretty sure it has an o-ring seal.
To flush out the old oil in the compressor, I'd fill it with new oil and shake it and drain it.

Unfortunately, I cannot give first hand advice on the compressor. My experience is with cci and sanden compressors.

​​​​​​Jeff

 

I agree with jeffwebley on this one. The system should be flushed well, and new oil and refrigerant filled.... AFTER drawing full vacuum on it and verifying that it has no leak-down over a few hours. You may also want to consider whether you retain the R-4 and mineral oil 'recipe', or switch over to R-134a and PAG oil with a modern Sanden compressor. Nothing wrong with keeping the 'stock' refrigerant, if you can afford it.

P.S. Just refreshing a 40 year-old system may not be enough for a long period of time. If the system had been up-and-running for those 40 years, I might feel differently. But, un-used seals, hoses, drier, etc. go bad just being, well, UN-USED.

 

I should have also mentioned if you were changing to R134a, you would need new compressor and lines.
Sorry

Jeff

 

if empty for some time you assume moisture and no clue on oil content. Inspect lines and compressor for shards, bits etc.. indicating potential issues?
if so i would flush (not compressor), and replace dryer (inspect for debris)..

step one secure r-12 after re-confirming nitrogen AND vacuum for time..and add oil and vacuum again and charge

 

I don’t see how vacuuming it down to boil out the moisture and the charging it with Freon to see if it works wouldn’t be worth a shot if your willing to risk the loss of a pump.
I mean if you’re looking at replacing the compressor, flushing the system, etc ,etc. then he risk of trying it as is might be worth it to you.
typically most systems loose the Freon over time and it stops working due to low pressure. So barring a large leak that reduced the level of oil present, it’s still in there.
if it’s R12 this could be an expensive experiment just due to cost of R12. More so if the pump burns up.

however if it’s 134a then it might be reasonable. AND ester oil is compatible with both 134a and R12. What’s in there now may be indicated by the ports that are on the lines/ compressor. If they are the quick disconnect type then it’s likely 134a. If the screw on type then likely R12 with mineral oil.

thing about 134a is that it will not carry the mineral oil. It will carry ester or PAG.

PAG and mineral oil do not mix. Ester will mix with either and will work with either Freon.

the pump is not Freon specific. I’m still using my stock pump with 134a and ester oil.

your main issue, as you pointed out is how much oil is in there. Short answer is there is no way to tell, so it’s up to you.

complete disassembly and flush and refill is the only way to know for sure.

 

I pulled a vacuum ( It's @28) and i will let that sit over night to see if it leaks down.
I just read the Chevy service manual it stated : Generally , compressor oil level should be checked only where there is evidence
of a major loss of system oil. Broken hose, severe hose fitting leak, collision damage... Also there is a way to check if it has oil.
So if it holds vacuum and has oil i might just roll the dice and charge it.

Reading my 1972 Chevy service manual , it describes how to drain the system of refrigerant.

NOTE: An empty 3 lb. coffee can with a plastic cover which has been cross-slit (x'ed), to allow hose entry ,works well for this purpose. Things are much different today.

 

Also dont run with compressor clutch engaged but for a few seconds..
It was stated no charge but again..if there was still some pressure in system there is a good chance i would add couple ounces watch gauges and go r12 charge..after of course long vacuum leak check... if truly empty and open im going in..

 

I was told by an A/C contractor that the vacuum in the system will suck in at least one can or more with out running the compressor .
After the system takes as much as it can that is when i should start the compressor .

 

I will be using R12

 

it will take freon.you stated the compressor ran when you replaced the belt and switches...my assumption is it either had refigerant in it or your nitrogen tricked the systen to think you have freon in it..running without r12 freon which carries the mineral oil may not do compressor any good.
measure your freon by weight and use gauges. Dont add until system does not take it.

 

thanks for your help.

 

Yes, things have changed, maybe its the education system. Owner's manuals used to tell you how to adjust the valves.. Now they tell you not to drink the contents of the battery!
VS

 

If not mentioned above, you need to replace the accumulator/drier if the system has been empty/air has gotten in. It has desiccant in it and that will be useless by now if it's been exposed to ambient air. It is standard practice to replace that component after the system has been open to atmosphere for any length of time. Just food for thought.

 

Op...when you drained nitrogen..wasit dry or wet (oil)when draining?
was there and pressure in system at all when you started?
did it hold vacuum overnight?
yes to all?
im addng 2 ounces (plus what may have estimated in emptying..)mineral (assumes r12) oil and charging by weight .
Your only loss of something goes wrong is the r12.
If compressor craps out it was due to die anyway..just an opinion if not disassembling...dryer etc..

 

I think it's most likely you'll find it'll work once you charge it up.

BTW your shop is way to clean and organized. Mine looks more like a flea market after some kind of explosion.

 

Ron
Yes, Ed is correct.
The system on my 69 was similar to yours in that it was all original and had not worked for many years.
I put in a pound of R12 (I have lots of R12) after doing a vacuum which held overnight. Then I fired her up and found I was actually getting cold air. Using an electronic sniffer (which you will enjoy having) I found a leak at the compressor shaft seal. (I believe yours is an A6 which is a very good compressor.) I bet yours will have a leak there, too. Also, pressures did not look right and indicated I needed a new expansion valve. (This system almost always needs a new one. Not sure if 71 system still using expansion valves.). Your hoses are probably fine. GM made very good AC hoses.
Sooo, off came the compressor which I resealed with a kit. Lots of videos on how to do. Its not hard. Getting the compressor off the car is the hard part.
Put in a new drier and expansion valve. Replaced all the orings I could get at. Lube them with mineral oil or nylog. (you can buy these parts at Old Air.) The drier will have a sight glass which is really helpful in getting your R12 charge right.
My system has been going great for 4 years now with the above repairs. There is a leak I cant find somewhere so I have to add about 12 ounces of R12 every spring. At that rate I am good for the next 40 years!
VERYSOON

 

Thanks for all the help. Great news my system held the vacuum over night @ 28 lbs the gauge never moved.