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how much oil, where to put it and other questions?

ploughna on Thu July 09, 2009 7:38 PM User is offline

Year: 1979
Make: Fiat
Model: Spider
Engine Size: 2L
Refrigerant Type: R134a
Country of Origin: United States

I'm installing an unused old aftermarket A/C system for my 1979 Fiat Spider. The system was designed for R12, so I've made a couple of changes as part of my conversion to R134a:

replaced the tube and fin condensor with a new parallel flow type
replaced the drier
replaced the expansion valve
replaced R12 charge ports with R134a
installed a new trinary pressure switch to protect the compressor and control the existing radiator fan
kept the compressor (Sanden SD508 with flare connectors)
kept the evaporator (with flare connectors)
replaced all hoses with new ones, but using a mix of flare and o-ring fittings because of the mix of parts described above.

There was no oil in my compressor apart from what looked to be like some residue, so I decided to flush it out with PAG100. I poured in about 6 oz, turned the compressor many times and emptied out again.

First question - when I emptied out, it didn't seem as if I got back out as much as I got in (although hard to tell because I spilled some). I did turn it upside down, opened the drain plug, turned the compressor over many times, even left it upside down overnight before concluding I was going to get as much as possible out. Can I assume for purposes of putting correct amount of oil back in that it is empty?

Next question - the Sanden 508 specs call for 7.2 +/- 0.5 oz of oil. Is the the amount for just the compressor, or for the entire system? Should I go on the low side of this tolerance if I think there might still be some residual oil in there per the first question, or how critical is the amount of oil anyway?

Next question - assuming 7.2oz is the total amount of oil for the system, where do I put it? All 7.2 oz in the drain hole of the compressor? I've searched the archives and seen it recommended to distribute the oil around the system (ie some in the compressor, some in the drier/accumulator, etc). Is this really necessary? If I must put some in the drier, does it matter which side it goes in (IN or OUT side)?

Final question - I don't know how much refrigerant the system should use - because it's aftermarket and now has non-standard components, the amount is not specified anywhere. What should I tell the A/C shop to do - start with a small amount and work up until correct? For reference, the condensor is 20 x 12 inches, evaporator is small (I don't know the dimensions), the compressor is SD508. Is there any rule of thumb to use here?

I appreciate your help with these questions - I went to a lot of trouble to get the installation right up to this point, and will be bringing to an A/C shop tomorrow to evacuate the system, check for leaks and charge it, so want to make sure I get it right!

Best Regards


chris142 on Fri July 10, 2009 12:33 AM User is offline

The 7.2 oz is the total system capacity for whatever the R12 charge amount was. When retrofitting you should add 3.5 oz of oil for every pound or R134a.

A 2lb system should get 7 oz of oil.

But since we don't know the capacity of the system were only guessing. I assume that it's going to be a small charge...2.0 lbs or less?

I always add more oil and never less. Yes too much oil can have a negative effect on cooling but In my opinion 2 or 3 oz too much oil won't hurt anything.

I'd put 8oz of oil in it myself.

ploughna on Fri July 10, 2009 2:22 AM User is offline

Thanks a lot for that info.

I wonder why is the SD508 data sheet so specific about 7.2oz +/- 0.5 oz when they have no idea of the refrigerant capacity of the system that the compressor is being installed in?


TRB on Fri July 10, 2009 10:20 AM User is offlineView users profile

Your Sanden is a universal compressor. Sanden wants at least the 7.2 ounces of oil used with this compressor no matter which refrigerant is being used. As for adding extra oil, it all depends on the size of the system components.


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