R134 converted ac systems charge level ???

My coronet was converted before I bought it.
And now have the system re-done and want to recharge it. Is the below amounts about right
1967 Coronet if it matters


Is there a general rule as to how much 134a is used in a system on an old car .
manual says 3lbs 6ozs of r12

Ive been told 80% is a good guide which equals to 2.68 lbs of R134

Factory system? Stock components? Condenser. evaporator. compressor,etc?. You may end up charging it based on pressures not quantity.

Yes.
All stock 1967 components.
New expansion valve and rec dryer

Find some R12. I tried converting to 134A on some old R12 systems and the results were not good.

I saw a chart recently, I’ll see if I can find it. Seems your number might be about what was on the conversion chart.

Interesting.

a buddy of mines 68 Coronet was converted above method and his blows ice cold and has for over 5 years now. He just cant remember the exact amount he put in it.

I charged mine this afternoon putting 36 ounces in it.
Its cold, Not as cold as the above 68 Coronet. BUT,,,,, based on my above 80 percent rule. It could use a tad more

I just dont want to go to far and risk damaging reed valves in the compressor

I assume you want to keep it looking stock. The oil used in the two systems is not compatible along with the some of the hardware(compressor). If is "re-done" that would mean all the oil (R12 oil) was removed and compatible(pag) 134 was installed. Adding the correct amount of refrigerant you should have good results.

https://www.techtownforum.com/knowledge-base/r12-to-r134a-conversion-chart-formula/

One thing I was told was to replace the hoses, the 134 will seep thru the old type hose. Your ends can be reused with the new hose.

I have done a lot of them and although the general rule is to use about 80%, I have had much better luck using the pressures.

Make sure you use the correct oil. The R12 in the old Mineral oil systems will not circulate in R-134a and will that will cause compressor failures. It will not hurt if it is in the system AND you use the correct oil, but it won't circulate to lubricate the system. Also PAG oil is not compatible with mineral oil. If there is any mineral oil in the system use ester oil not PAG. I use ester only in R12 systems even if I am not retrofitting just in case.

I charge the system until the low side gets near 30 to 40 and the high side gets about 200. From there I feel the air temp and add a little if needed but do not let the high side get too high. The old systems do not have a high side cutoff and R134a pressures climb fast in hot weather.

As stated, R12 while hard to find is a better refrigerant.

And if you find it you need a license to buy it

The car had been converted long before my purchase.
It was empty when i bought it. Previous owner told me was bad condenser...yet ive found no signs ot that.

Ive replaced a bad hose .. and expansion valve and will be replacing the dryer as well.
Ive got 36 ozs in it right now to ck operation and for any other leaks. So far...so good.
On the drive home yesterday. It was cool and comfy...but feel like it could / hope would be a little better.
I havent put a thermometer in the vent yet.


And planning to evac it back out . Change the dryer. Then pull a good vacuum on it for like an hour or so .

Was curious the anount required to recharge it. Ill start with the same 36 ozs for now and see what pressures i get.

https://ww2.epatest.com/epa-609-mvac/

Some people convert by draining the R12 and refilling it with R134a & Ester oil and others will drain, flush, replace the oil in the compressor sump, and replace the hoses & O-rings. It's a crap shoot how it was done if you don't do it or see it done, but no biggie.

If you run ester oil you will be fine if they didn't remove the mineral oil. When you replace the dryer if the o-rings are black they didn't replace them. Old school rubber was black. Newer HBNR are usually green but sometimes blue.

I have found that the old rubber hoses and rubber seals will leak the R134a to the tune of about 12 oz per year. This usually means that in the spring you may need to top it off and you would be good for the year.
If you are loosing more than that look for a bigger leak.

If you replace all the hoses with newer "barrier' hoses and the o-rings/seals with the new HNBR then it should hold a charge a lot longer but the oem compressor seal was made for lower pressure R12 so it may still loose pressure over time.

Good news is if you don't have a noticeable leak you should not loose any oil.

As SRT said R12 requires a license but craigslist /ebay is a good source for people who are not interested in licenses. Just sayin...

Ive done all new O rings myself.
I have no problem changing compressor oil. Thats easy . Just to be on the safe side. I will pick up a bottle of ester oil when I pick the dryer up today

The rule is to multiply the R12 fill spec by 0.9 then subtract 0.25 pounds from the result.
Example 40 oz. of R12 = 2.5 pounds X 0.9 = 2.25 pounds minus 0.25 = 2.0 pounds of R134a. Keep in mind those small cans are only 12 oz.
Additionally if you would like it to cool better put an auxiliary fan on the condenser then you can add a few more ounces of refrigerant. Keep the high side around 250 psi.

Keep in mind there are fake forms of what they call "R12" but contains flammable chemicals/CFC's.

https://www.aa1car.com/library/tr497.htm

I start with 70% of R12 weight. Check your pressures after coming back from a drive on a hot day. Add more if pressures will allow. Buying a new modern design condenser made for r134 will help a lot with cold air temps as measured at the dash.

First choice though is R12. R134 is a smaller size molecule and designed to run at higher pressures, both of which can cause problems with leaks in an r12 system.

Best rule of thumb I have seen is to charge to a high-side pressure (in psi) of 2.2 to 2.5 times the air temp (in F) in front of the condenser/grille. That's how I do all my cars.
If you're charging to 250 psi on an 80F day I think that's too much.


Oh, and drain and flush as much of the old mineral oil as you can. It doesn't mix with the PAG oil used for R-134a, so it's taking up space in the system somewhere (even if it just sits in a low spot, usually the receiver/dryer).

How is this possible with crimped ends? One of the reasons I'm asking is PS hoses. I've looked under all the rocks I could think of and never could find a procedure to re-use those hose ends with new hose. I would think A/C hoses are similar.

Still with just the 36 ozs in it and the original receiver drier ( which I plan to change this week )
But so far, I think its working damn good

the OE water valve doesnt close so for now I have the heater core bypassed altogether . I just got an nos valve earlier this week I need to replace same time while drier is getting replaced

BUT,,,, center outlet temps are,,,,,,and This is sitting in the garage,
at 85 degrees ambient temps , slightly above idle,