total amount of pag oil for a brand new a/c system

[Ray70Chrg]

I have just completed putting together a brand new a/c system on a '70 charger, 383 engine. every component is identical to the original parts except for the compressor which is a Sanden 5DSH. The compressor came with 4.5 ounces and the instructions stated "that it was sufficient for the whole a/c system that is was designed for". They don't list anything about what systems that they were designed for.

The '70 fsm states the whole system should be 10-11 ounces. This includes the RV2 compressor and 2 mufflers. My question, to anyone who has done this, how did you determine the correct amount of pag oil for your converted system.

4.5 ounces seems too little, and 10-11 ounces seems too much

 

[Bighouse]

I’m not so sure anyone’s going to have a solid answer. In the meantime maybe check out what other cars requirements are with similar sized components and the sanden compressor from the factory. Maybe there’s a refrigerant-to-oil ratio that a happy medium.
Just thinking out loud

 

[threewood]

I would go with what the manufacturer put in the compressor for use. These systems are not very large and linesets and evap/condenser are about equal sizes. If you add too much oil in, it will degrade the cooling capability.

Is there a sticker on the compressor? It states oil fill.

 

[Rishi]

I think you'll be fine 4.5 ounces (135ml) because the oil is mostly for the compressor. It flows through the system, but if that's all they (Sanden website) say you need, they may be right. That compressor is a newer generation, lighter, more efficient, etc.

I'm not surprised the FSM on the older (OEM) compressors calls for more oil.

Too much oil creates problems. If you chose to double it, for example, to 8oz, and the compressor failed, you may have a problem getting the warranty fulfilled, compared to following their directions and it failing.

 

[oldbee]

According to my failing memory, add maybe an ounce for evaporator & maybe 1-2oz. for condenser. A little oil lays in the bottom of both while operating. Freon rushing by picks up a little & drops off a little.

 

[Ray70Chrg]

I would go with what the manufacturer put in the compressor for use. These systems are not very large and linesets and evap/condenser are about equal sizes. If you add too much oil in, it will degrade the cooling capability.

Is there a sticker on the compressor? It states oil fill.
View attachment 1767797

No, mine did not come with that info on the label, however, I finally dug deep in the Sanden site to find they are only concerned with the the % of pag oil to the volume of refrigerant. The volume of the entire system is not a concern until you get to very long hoses being used in system.They claim that these style compressors are most efficient when pag oil is 3.3 to 8% of charge volume. My compressor came with 4.5 ounces of oil and my target starting point for refrigerant is 41 ounces which will leave me with 11.45%. For each additional ounce of refrigerant added it brings the % down about .5%. When figuring out these values, pag oil must be measured in cc,s and refrigerant measured in grams. Thanks again for responding.
RAY

 

[Bighouse]

Good info right there. What you’ve done is on my list of things to do. Factory A/C with the modern compressor.

Please come back with your results!

 

[Ray70Chrg]

Good info right there. What you’ve done is on my list of things to do. Factory A/C with the modern compressor.

Please come back with your results!

I will follow up, however, I've been fighting the flue bug for the last 7 to 10 days so it will some the in the next week.

 

[nitro_rat]

As a rule of thumb, compressor gets whatever is recommended for that type (yours is factory filled in this case), and each other component gets one oz. One oz in the dryer, one in each hose, one in the evaporator, and one in the condenser. Some monster systems I give an extra oz in the dryer and/or condenser. This also spreads the oil throughout the system to get it circulating quicker on start-up. I've never had a problem with this method and I have converted a bunch of cars to 134a. Using a parallel flow condenser is the biggest thing you can do to bring system performance up to par on a conversion.

 

[Ray70Chrg]

Good info right there. What you’ve done is on my list of things to do. Factory A/C with the modern compressor.

Please come back with your results!

Well, got back to it a few days ago and pulled 28in. vacuum for 45-60 minutes and it held steady overnight and during the next day, so I was confident the system was tight. Tried to charge system with refrigerant and engine running and the compressor would not engage. Had a reading of 30psi, on the low side, after the 1st 12 oz. can. While putting in 2nd can I had a reading of 42in. and compressor still not engaging. Stopped the charging process, concerned that the new low-pressure switch is not functioning properly. I have 12v at the switch and when I touch the compressor lead to the battery the clutch engages. At a standoff right now investigating new switches. Ordered a Bouchillon #6662 which is both a hi/ low switch and fits the dryer which are on these a/c systems. The questionable switch came with the new dryer and has no specs as to when it opens and closes. I ordered it on ebay and it is a Four Seasons unit which is the same dimensions and proper fittings for my application, however, it was manufactured in China.

 

[nitro_rat]

Sometimes you need to jump the switch to force the compressor on to get the system to start taking freon. Once you’re up to around 100 psi it should be able to function on its own.