Automotive Air Conditioning Information Forum (Archives)

ploughna on Tue August 11, 2015 9:10 PM

Year: 2015
Make: custom
Engine Size: 3L
Refrigerant Type: 134a
Country of Origin: United States

I'm fitting a custom A/C system in a kitcar that I built and not sure about the amount of oil required.
All components are new and the compressor came pre-filled with 6oz PAG46 and instructions not to add any more. It's an SD7H15 (Sanden equivalent/copy, made in China)
However, the Sanden manual lists 4.5oz if using a TXV or 8oz if using a CCOT (and under 40oz refrigerant). My system is TXV.
What's behind the 6oz preload from the compressor vendor then - I know oil gets distributed around the system - is the idea that some of the 6oz is dispersed and there is close to the recommended 4.5 left in the compressor, or should I empty some out of the compressor so that there is a total of 4.5oz in the system?
Also, my car is mid-engined, so the compressor is about 6ft behind the evaporator and the condensor about 2ft in front of the evaporator. Should I take these longer than normal lines into account and have more oil. Sanden mention this scenario in their documentation, but the recommended quantity only increases if lines are very long as in a truck or bus. When I run their formula it barely makes a difference and still comes out at 4.5oz, so the question remains - 4.5oz, 6oz, or something else?
How critical is the amount anyway? Sorry if I'm overthinking it, but all help appreciated

Here's what Sanden have in their service manual:

6.8 Oil Charge
• Oil Circulation Ratio (OCR) should be between 3.3% and 8% ratio of oil to refrigerant
by weight.
A
Less than .2 mm (.007 in)
in either direction
10
6.8.1 Oil Flow Theory
• Compressor lubrication occurs as the oil which circulates with the refrigerant passes
through the compressor crankcase during operation. The Sanden SD series
compressor achieves optimal durability and cooling performance when oil circulates
through the system at a ratio of 3.3% to 8% oil to refrigerant. Excess oil can act as an
insulator limiting heat transfer in the evaporator and condenser, while too little oil can
negatively affect durability.
• Oil will collect in low pressure cool components (evaporator, accumulator and suction
hose) of the refrigerant loop. For example a long suction hose which sags can collect
several ounces thus reducing overall oil circulation ratio.
6.8.2 Oil Charging
6.8.2.1 Passenger Car, Light Duty Truck Single Evaporator
Refrigerant charges 24oz (680g) to 40oz (1133g)
• 135cc oil TXV systems (4.5 oz)
• 240 cc oil in orifice tube systems (8.1 oz)

Best Regards
Paul

Edited: Tue August 11, 2015 at 9:48 PM by ploughna

bohica2xo on Wed August 12, 2015 11:18 AM

I would leave the full 6 ounces in it to start with.

Oil migrates back to the compressor on the inside surface of the suction line. With a 1/2" ID hose 6 feet long, you will have about a half ounce of oil in the hose while the system is running. When it stops the oil winds up in the lowest point of the line. The high side moves the oil in solution with the liquid refrigerant.

At this point you don't know the system capacity. But you do know the oil in the system. Charge it to the point of seeing mostly liquid in the sight glass, and shit it down. With the refrigerant quantity known, calculate the current oil ratio.

Adjust the oil charge if it is too low. Unless you hold more than 72 ounces, that is obviously not necessary. On motorhomes adding oil is the norm. Finish charging is a balancing act of adding small quantities while observing the high side at full load. You will reach a condition where refrigerant is being stored in the receiver, and pressures are stable. This should be done at 2500 engine rpm, doors open and cabin fan on highest speed.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

ploughna on Wed August 12, 2015 3:08 PM

Thank you - that helps a lot. I'm guessing my system will take less than half the 72oz number you mention for refrigerant, so per your feedback, there should be plenty of oil.

While I'll definitely proceed as you've advised I was wondering at what point could there be too much oil, or am I not thinking of it the right way - for example if I have 6oz oil in the system and 24oz R134a, does that give me a ratio of 25% which is significantly higher than the 3.3-8% ratio mentioned in the Sanden documentation? Or is there some retained in the compressor that doesn't count toward that calculation?
Best Regards
Paul

Edited: Wed August 12, 2015 at 3:08 PM by ploughna

ice-n-tropics on Wed August 12, 2015 3:36 PM

1) For a USA made SD7H15 with normal txv 135 cc of oil is optimum for cooling
2) For China knockoff, extra oil including some mineral oil is best to get-er-going w/o immediate lock up.
TRB: For rebuilds and China Knock offs, I recommend 2 oz of 5gs (Napthic) or GM (parafinic) refrigerant mineral oil which will stay in the crankcase for quite a while to get-er done through warranty
3) The SD7H15 will retain approx 2 oz of oil in the crankcase at mild conditions
hotrodac

-------------------------
Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

Edited: Thu August 13, 2015 at 11:11 AM by ice-n-tropics

bohica2xo on Wed August 12, 2015 11:22 PM

good to see ya hog killa

Paul:

Ice covered the 2 ounces in the crankcase, add that to the .5 ounces in the return line. That takes you down to 3.5 ounces. Should be a good starting place, especially with a new & dry system



-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

ploughna on Thu August 13, 2015 2:34 PM

it's all starting to make sense now - thanks again for the explanations and advice.

in the meantime, I've decided to return the Chinese Sanden copy and get the actual Sanden branded one (price difference is only $20 + shipping) - maybe the one I have is just fine, but it'll make me feel better!!
does that change anything? The Sanden part is supplied by Vintage Air - who said that it's 'prefilled' by the manufacturer, no need to do anything, but they don't state the quantity. The label does say 240cc SP-15 (it's not clear to me if that's the qty actually in there or simply the capacity)
Should I just install it with the amount of oil that it's shipped with or empty it out and measure it and adjust per the quantities discussed above?


Edited: Thu August 13, 2015 at 7:42 PM by ploughna

bohica2xo on Thu August 13, 2015 8:24 PM

Ice says 4.5 ounces, add .5 for the long return... 5.0 to 6.0 ounces should be good to go. I would drain and check if they say it has 240cc's in it - that would be prepped for CCOT installation.

I am sure Ice will be by to add his expertise as well.

.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

ploughna on Fri August 14, 2015 11:25 PM

Sounds like a plan.

Thanks again

Edited: Sat August 15, 2015 at 1:06 PM by ploughna

ice-n-tropics on Mon August 17, 2015 4:55 PM

Agree on 5.5 oz total for medium long hose w/ txv if it is a genuine Sanden SD7H15
If a compressor is drained for a hour w/ occasional turning, 20 to 30 cc of oil will cling inside the crankcase and head and not drain
hotrodac

-------------------------
Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod