looking for amount (oz) of coolant needed for a/c recharge 134a r12 refrigerant

[zimvsdib]

My system has a slow leak and is been really hot in LA this summer. it was 95 today.
Anyway i was going to recharge the systems in my cars.
i have a 134a system and a r12 system

I did a bit of searching online but i couldn't find the amount required to fill the system.
Most cars have a sticker with for example "19oz of refrigerant required"

looking for amount requirements for 134a and r12


i've been told not to convert the r12 to 134a (i guess r12 is way cooler) so thats why i have both currently.

[sdg3205]

How much you need depends on how much you've lost. The volume will be in the workshop manual. Do you have gauges?

R12 is so damn expensive it would be economically prudent to find and fix your leak, THEN recharge.

R12 vs R134a is a big ol can of worms, but I have had cars with both and I'd do my best to maintain an R12 system if possible.

[David T]

How much you need depends on how much you've lost. The volume will be in the workshop manual. Do you have gauges?

R12 is so damn expensive it would be economically prudent to find and fix your leak, THEN recharge.

R12 vs R134a is a big ol can of worms, but I have had cars with both and I'd do my best to maintain an R12 system if possible.

According to St-29-11/81 the refrigerant charge was changed from 2.75 lbs to 2.2 lbs for R-12. If you put R-134 into a system that was designed for R-12 the rule-of-thumb is to use 10% less or 2.2-.22 or about 2 lbs of R-134. Of course after changing the oil. This also translates into a 10% reduction in the capacity of the system. Again using a rule-of-thumb, you need roughly 1 lb of refrigerant to get 18,000 BTU's of cooling. Less refrigerant = less cooling. So, in a system that was originally designed for 2.75 lbs you now have 2 lbs. A significant loss of capacity. You won't notice it on a cool day but on a really hot day you won't achieve a delta T of 20 degrees (the temperature difference between the outside ambient air and the interior compartment temp). R-12 is still obtainable and is not all that expensive since you only need 2.2 lbs (2.75 if you go by the old spec and want all the cooling you can get!). It is expensive enough that you should get the system as tight as you can so you don't lose much.

[mr_maxime]

DMCMW put R12a in my car. It's a bit off topic, but it was about 1/3 the price of R12. I think they also dyed it in case it leaks.

[zimvsdib]

Awesome. Thanks for the information.
I do have a set of ac manifold gauges but no electric pump yet.
My systems are empty at the moment. To my understanding the only way to diagnose the leak location is to recharge with UV dye and find it.

I was told that the majority of leaks are from the compressor fittings.

[davidc89]

Awesome. Thanks for the information.
I do have a set of ac manifold gauges but no electric pump yet.
My systems are empty at the moment. To my understanding the only way to diagnose the leak location is to recharge with UV dye and find it.

I was told that the majority of leaks are from the compressor fittings.

Usually it's the hoses. Make sure you have a set of gauges for r12 and r134a if you plan on using both. You don't want to mix refrigerants.

[David T]

Usually it's the hoses. Make sure you have a set of gauges for r12 and r134a if you plan on using both. You don't want to mix refrigerants.

The leaks are the hoses and the "O" ring seals. When you replace the hoses you also replace all of the seals. There are drop-in replacements for R-12 but none of them work as well although they are less expensive. To find leaks the system is pressurized to 200 psi with Nitrogen and you look for leaks with leak detector solution (soapy water). If you have a system that is "flat" and has been for some time you should replace the dryer/accumulator along with all 3 hoses and seals. You should also remove the oil from the compressor and put in fresh.

[ed uding]

They system is simple to rebuild for R134A and the temp output is the same.
you neat to swap the accumulator and orifice tube, and o rings.
Refill it with 920 Gram R134A and turn the low pressure switch (Center screw) 360 degree back. You have a less flex gas compare to R12.
165 CC new PAO oil. Problem with the R12 and R134 oil, is they don,t mix. And your A/C pump will brake down by running with to less oil. The oil will get stuck in the accumulator and no longer flow with the gas a round in the system.
We do a 25 car a year for 14 years on a row, for all Europe. Hot and cold Countries, from Norway to Spain


Ed Uding
www.delorean.eu

[zimvsdib]

okay I'm going to refill my r134a system (that has a very slow leak) with 32oz of uv refrigerant.

Do i need to add any oil to the system? Mind you I didn't take anything apart or replace anything yet.

[David T]

To determine if you need to add any oil you must measure what is in the compressor. The procedure is in the Workshop Manual N:10:03-:04. To make the dipstick go to the Sanden website. Best practice is to remove what is in there, measure and put in fresh. Instead of UV dye you can also use regular leak detector dye that can be seen without UV light. They also make a leak repair kit now you can shoot in and it is supposed to stop minor leaks. I have not personally tried it yet but I am told it works for small leaks.

[Ron]

okay I'm going to refill my r134a system (that has a very slow leak) with 32oz of uv refrigerant.

Do i need to add any oil to the system? Mind you I didn't take anything apart or replace anything yet.
If you are confident that the oil was correct when installed and there are no signs of oil at any of the fittings/hoses/etc, you are probably ok. But if you are going to evacuate it (you should), do the check David mentioned anyway.
Note since the ports are right at the compressor, oil may come out with the refrigerant if you let it out too fast...