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How much a/c oil for entire system?

Joined
25 October 2007
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820
Location
Saint Johns, FL
I had a compressor go bad on my 1991 which is still R-12. I plan to do a complete flush of all the components and lines. I bought a new Denso compressor, and will also install a new expansion valve and receiver/drier, change the o-rings (except for the evaporator) and then finally vacuum the system. I will be converting to R-134a. I guess I'll use ester oil with the new freon instead of PAG. I'm not planning to change the rubber lines to the compressor.

After a complete flush such as this, how much total oil should be installed?
 
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I could be completely wrong but 120 ml? That's the amount the A/C conversion kit contains.
 
I could be completely wrong but 120 ml? That's the amount the A/C conversion kit contains.

Thanks for the reply, Gold! 120 ml seems to jive with the service manual assuming you're replacing (or flushing) the: condensors (20 ml), evaporator (10 ml), receiver (10 ml) and compressor (80 ml).

I was looking at the 1991 Service Manual and it says to add this much oil after replacing the following parts:
Condensor 10 ml
Evaporator 10 ml
Line or Hose 20 ml
Receiver 10 ml
Compressor - measure the volume of oil drained from the old compressor, subtract that volume from 80 ml, then drain the difference from the new compressor.

With this compressor subtraction procedure, I guess the manual assumes the compressor normally holds 80 ml and if you can't drain that full amount from the old compressor you removed, then the rest of the required oil must be elsewhere in the system? Seems a strange procedure to me.

Why can't they just say how much oil the entire system should hold?

Also, regarding the instructions to add 20 ml when you replace a line or hose, there are 6 pipes and 2 hoses, all of varying lengths and volumes. If I add 20 ml for each one, that's 160 ml, which seems way too much. I have an 8 oz. (236 ml) bottle of Ester with dye, which is surely enough, but I don't want to put in too much and displace the volume that freon should occupy.

Can someone who has a conversion kit tell me if the instructions specify how much oil to add?
 
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why not just convert to the new R134a, it uses less gas, and doesnt kill the life of your compressor, R-12 is Old and not as effective as the new R134a

the upgrade kits cost around 45-50 bucks

and how much did you pay for your new compressor? the 1991-1995 acura Legend compressor is the exact same as the NSX and it cheaper.

goodluck
 
why not just convert to the new R134a, it uses less gas, and doesnt kill the life of your compressor, R-12 is Old and not as effective as the new R134a

the upgrade kits cost around 45-50 bucks

and how much did you pay for your new compressor? the 1991-1995 acura Legend compressor is the exact same as the NSX and it cheaper.

goodluck

I am converting it to R134. Not because R134 is more effective, but because it is readily available for the DIY'er. I bought a brand new genuine Nippon Denso 10PA15C compressor for $148 shipped by making an offer to an a/c dealer on ebay. By far the best deal around. I have a new receiver/drier, expansion valve and o-rings. I have a can of the a/c flush solvent and vacuum pump to suck out all the moisture and remaining contaminants. Now, I just need the time to get in there and do the job.... and the info on how much oil to add.:smile:
 
R-12 is Old and not as effective as the new R134a
This is vice versa. R12 has better cooling capabilities than R134a.

NSX-Files: If you would have converted it without a new compressor I'd recommend to just fill in the content of the conversion kit into the system. One question: Is your new compressor for R12 or R134a?
I've asked a similar question some time back and one guy answered that it's hard to tell the amount of oil remaining in the system if you have a leak like I had. R134a takes 10% less, 850 than 950 grams. If you put in 120 ml ester oil dor R134a you've 120 grams in the system or 200 ml if the new compressor already contains 80 ml ester oil. I guess that the system would work also. But again I'm no A/C guru.

In my system I had a leak over years so it's a very wild guess how much oil is still in there but I'm waiting for the compressor to blow up anyway until I give the system a complete overhaul. :) Good job on the o-rings BTW. Be careful not to twist the fine lines by much. A haircut could be the result.

In Europe we have R413 which is a sustitute for R12 but works fine with mineral oil. But I don't see a reason not to convert directly to R134a as Honda sold the kit. :)
 
Well I was told that these AC/ guru's hit and miss, I mean they just keep replacing parts they think are bad, and by the end you have all new parts and they have a big check in the bank. LOL

and GOLDNSX you are right, the R-12 is a better cooling gas. I forgot. sorry.
 
So I have removed the A/C receiver/drier, the expansion valve, the compressor and hoses. I believe one of the hoses has a leak in the swaged (sp?) fitting between the rubber hose and the pipe fitting. So I am going to get them both rebuilt using new barrier hose. Because of the holiday, that won't happen until next week though.

My old compressor was basically worn out and was very weak the last time the a/c shop put R-12 in it. It showed the signs of leakage near the front of the compressor (apparently common for the Denso), and had barely any oil in it when I drained it out.

Some questions:
While I was working on the car, it occurred to me that I'm not sure what will happen to the ester oil I pour into the new compressor, once I connect the air vacuum pump and evacuate the system. Does the oil remain in the compressor, or does it get sucked out by the vacuum pump?

I've read of people evacuating the system, then adding the oil charge from a can tap through the yellow service line on the manifold gauges. Since the system is under vacuum it sucks the oil in. However, my ester oil is in a regular plastic bottle so I can't do it that way. I was just going to pour the correct amount of oil into the compressor. Do I need to get the metal can oil charge instead?
 
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This is vice versa. R12 has better cooling capabilities than R134a.

NSX-Files: If you would have converted it without a new compressor I'd recommend to just fill in the content of the conversion kit into the system. One question: Is your new compressor for R12 or R134a?

The new compressor has a Denso sticker on it that says "R-12". But, I'm sure it's compatible to run whatever freon you want as long as the incompatible oil is flushed out. I'm going to drain whatever oil is in the new one, pour some ester in there, swish it around and drain again, flushing the oil out to avoid any chance of "black death". Then I'll put in new ester in the correct amount (assuming I can definitively figure out what amount that is).

Thanks for the help so far!
 
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The new compressor has a Denso sticker on it that says "R-12". But, I'm sure it's compatible to run whatever freon you want...
This is correct. The seals can stand both, R12 and R134a. I've contacted Denso Germany and they assured me this. The only difference are the fittings for the (expensive!) hoses. But the fittings can be changed between the compressors.

Good question on the oil in the compressor. I think it's a separat reservoir which doesn't get mixed with freon and won't get sucked out while vacuuming.
 
Alright, I finally got my a/c system back together. I disconnected all the pipes and hoses then flushed all the lines, evaporator and condensors with the solvent then blew through each with compressed air. I reassembled all with new green o-rings, new filter drier and new expansion valve.

On advice of the a/c shop I only had the high side hose rebuilt with barrier hose and new crimped fittings. They basically cut off the old hose barbs then aluminum weld hose barbs onto the original pipes then crimp on new ferrules to the new hose.

I found an a/c repair manual I had from years back (late 1980s) which indicated the Denso compressor holds about 2.6 to 3.4 ounces of oil. It says the typical total system volume of oil is 7.2 ounces of oil. I figured since the car is mid engine it probably holds a little more oil since there is more pipe length. So I poured in 7.5 ounces of ester into the compressor then installed it. I then evacuated the system for 45+ minutes.

When it came time to recharge, I had difficulty getting the system to take freon. Even after trying to put in 1.5 cans of R-134a I couldn't get more than 40psi on the high side gauge. So I called it quits and went on vacation for a week and thought about possible reasons for the problem. I figured the compressor belt was slipping so when i got back the first thing I did was tighten that. That seemed to fix it as then I was able to build high side pressure up to 125psi. My low side was still under 20psi and I still had lots of bubbles on the sight glass and warm air on the driver side vent. I continued trying to get the system to take more freon. It has about 2.5 12oz. cans or 28 oz of freon (each can is 11oz freon and 1oz lubricant). My high side has continued to rise and is now probably too high. I was shooting for 250 psi but it is nearing 300psi and the low side is only at 25-30psi and I still have bubbles on the sight glass. The air is cool/cold, at best 59 degrees.

I didn't realize at the time but since the freon cans have one ounce of lube each I am now nearing 10 oz of oil. I had planned on it only having the 7.5 I poured in the compressor. I think that's the reason I have such high pressures on the discharge side even when there is not enough freon to properly cool the car and get rid of the sight glass bubbles. I figure the extra oil which is not compressible is taking up volume that should be occupied by freon.

Am I on the right track? I certainly don't want to over-pressurize the system but I want it colder. So I'm thinking I have to take the compressor out again and drain about 6 oz of oil. That's a total PITA but do I have any other options? I'll have to start over with evacuating and recharging too so I'll have to give away the R-134a to some a/c shop and buy another 3 cans.

Thoughts or advice?
 
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