Automotive Air Conditioning Information Forum

How do you guys go about figuring out the oil amount for a custom system?

The compressor came with 3oz of PAG46

Thanks

Given the very large evaporator you are using, the line lengths and large receiver in your system, I would treat it the same as an Expedition or Excursion using the same FS10 compressor with Rear A/C.

Expedition:
1997 All Eng.; w/ Rear AC – 13.00 Oz. PAG-46; 62.00 Oz. R-134a

Excursion:
All Eng.; w/ Rear AC – 68.00 Oz. R-134a; 14.00 Oz. PAG-46

E350 Van
2002 8 Cyl. 5.4 Eng.; w/ Rear AC – 13.00 Oz. PAG-46; 46.00 Oz. R-134a

So 13 to 14 ounces total.

Put the extra oil in the receiver or the liquid line.

bohica2xo wrote: ↑Thu Oct 12, 2023 1:33 pm Given the very large evaporator you are using, the line lengths and large receiver in your system, I would treat it the same as an Expedition or Excursion using the same FS10 compressor with Rear A/C.

Expedition:
1997 All Eng.; w/ Rear AC – 13.00 Oz. PAG-46; 62.00 Oz. R-134a

Excursion:
All Eng.; w/ Rear AC – 68.00 Oz. R-134a; 14.00 Oz. PAG-46

E350 Van
2002 8 Cyl. 5.4 Eng.; w/ Rear AC – 13.00 Oz. PAG-46; 46.00 Oz. R-134a

So 13 to 14 ounces total.

Put the extra oil in the receiver or the liquid line.

Thanks bohica2xo for that info, seems in line with MACS article (below) and there are still some outstanding questions.

These are the ratios for the model information provided

Model / oil oz / R134a oz / oil ratio
Expedition 13 62 21%
Excursion 14 68 21%
E350 Van 13 46 28%

Thoughts on the following?

1) Conflicting oil ratio %. See Sanden vs MACS conflicting references below
2) Calculated oil requirement based on 25% rule:

Figuring out Refrigerant capacity (please check my math below)

Item / refrigerant oz / oil oz@25%
Hoses 11.10 2.77
Receiver/drier(2”x7”tall - typical) 7.94 1.98
Receiver/drier(4”x7”tall - large) 31.74 7.94
PF Condenser?
Evaporator?
Compressor? (shipped with 3oz)

With “typical” drier about 5oz oil so far on 19oz of R134a
With “large” drier about 11oz oil so far on 43oz of R134a

for the receiver/drier I estimated R134a liquid capacity at 60% of volume to account for desiccant/pipes/etc.

Thanks,
Andy

***Oil % differences references

Oil ratio Sanden 3.3%-8% vs MACS article “the 25% rule” which corresponds to the info given by bohica2xo. The MACS article seems to take many different compressors as a whole.

- Sanden Service Guide 3.3%-8%

“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.”


- MACS Article 2018 - THE 25% RULE "Our struggle with oil"
Pg 24
https://www.macsw.org/WEB/images/Macs_D ... i42MC4wLjA

Pg 28/29
"
THE 25% RULE
For a long time, we used a rule of thumb that basically said that the oil charge amount is generally around 25% of the total refrigerant charge amount. For example, if you’re working on a 2011 Kia Sedona (with a 3.5L V6), the specs say it takes 900±25cc (about 31 ounces) of R-134a and 210±10cc (about 7.25 ounces) of FD46XG PAG oil. Do the math, and you come up with about 23% (try this on a few more vehicles, and you’ll get similar results).

Figure 5: Many vehicles from the last 10 years are using oil separators, which result in greatly reduced oil charge amounts in some systems. Pay close attention if one of these shows up in your bay. Models from just a few years ago may have required double the amount of oil. Even though the number may not look right, it probably is, and adding too much oil can be detrimental to the system.
"

***refrigerant/oil calculations

- RedDot Refrigerant guide 2009
https://www.btrac.com/documents/refrigerant-guide.pdf

"
AC systems with LESS THAN 3.5lbs(56oz/4.66-12oz cans) of R134a
5 cyl or less:
[R134a(lbs)*2]+1.35=total Oil Charge (oz)
7 cyl or more:
[R134a(lbs)*1.07]+2.4=total Oil Charge (oz)

AC systems with MORE THAN 3.5lbs(56oz/4.66-12oz cans) of R134a – On Vehicle Testing Recommended.
"

*At 3.5lbs the calculation above yields 8.35oz oil. Likely not fully accurate with longer hoses and larger receiver/drier

- Refrigerant calculations

Hose Refrigerant and oil
Type Size lb/ft oz/ft ft Total lbs Total oz Oil @25%
HPV 8 0.0043 0.0688 15 0.0645 1.032 0.258
HPL 6 0.0346 0.5536 18 0.6228 9.9648 2.4912
LPV 10 0.0011 0.0176 6 0.0066 0.1056 0.0264
Totals 39 0.6939 11.1024 2.7756

R134a OZ/cubic inch From RedDot document
5/16 ID
5 Numerator
16 denominator
0.3125 Diameter
0.15625 radius
12 in tall
0.92039 ci/ft
0.0346 lbs/ft From RedDot document
0.03759276 lbs/ci
0.601484153 oz/ci of R134a


Large
drier
7 h
4 d
87.96 ci
60% liquid volume (less dessicant etc)
52.776 ci liquid refridgerant
31.74 oz refridgerant
25% oil ratio
7.94 oz oil

Small
drier
7 h
2 d
22 ci
60% liquid volume (less dessicant etc)
13.2 ci liquid refridgerant
7.94 oz refridgerant
25% oil ratio
1.98 oz oil

First, and foremost the FS10 is NOT A SANDEN. FS10 compressors like some oil in circulation.

Second, Oil Circulation Rates have many changes from system to system.
For instance, years ago when Harrison A6 compressors were OEM, Harrison told us an OCR of 10 to 12% was a good number, in a system where the compressor itself has an 11 ounce sump with a built in oil pump. We were told by Harrison the added oil was just fine expanding in to foam after the TXV, and somehow aided heat transfer. Years later a heat exchanger engineer told me that was completely wrong...

As you have already deduced the OEM large systems with an FS10 have a larger OCR. Your choice of a very oversized receiver / dryer will need some additional oil to properly balance the system

I will point out however that the vehicles I used as an example have very large accumulators. 3.50 x 11.0 inches on the E350, and 88mm x 280mm on the Expedition.

You will need to make some allowance for the unusual receiver you are using. The line lengths mimic a dual air Expy or Van. You can get close, and if you need significantly more refrigerant than one of those vehicles, you can add the percentage of additional oil along with the added refrigerant.

Sanden Info is based on oil circulation ratio OCR with 1 to 3 ounces remaining in the swashplate compressor crankcase and cling oil remains in AC components.
OCR = weight of oil in circulation at any moment divided by weight of both oil and refrigerant in circulation and varies with operating conditions. More oil remains in crankcase at low rpm. E.G., Minimum requirement for Sanden OCR is about 4 to 5% for scroll but basically no oil remains in scroll crankcase.
Accumulator can hold 3 ounces of oil under some operating conditions.
hotrodac (MACS Trainer License #115)

ice-n-tropics wrote: ↑Thu Oct 19, 2023 6:01 am Sanden Info is based on oil circulation ratio OCR with 1 to 3 ounces remaining in the swashplate compressor crankcase and cling oil remains in AC components.
OCR = weight of oil in circulation at any moment divided by weight of both oil and refrigerant in circulation and varies with operating conditions. More oil remains in crankcase at low rpm. E.G., Minimum requirement for Sanden OCR is about 4 to 5% for scroll but basically no oil remains in scroll crankcase.
Accumulator can hold 3 ounces of oil under some operating conditions.
hotrodac (MACS Trainer License #115)

The man has returned. Nice to see you, Ice. I hope all is well and the pond is full of fish.

Agree!!!

ice-n-tropics wrote: ↑Thu Oct 19, 2023 6:01 am Sanden Info is based on oil circulation ratio OCR with 1 to 3 ounces remaining in the swashplate compressor crankcase and cling oil remains in AC components.
OCR = weight of oil in circulation at any moment divided by weight of both oil and refrigerant in circulation and varies with operating conditions. More oil remains in crankcase at low rpm. E.G., Minimum requirement for Sanden OCR is about 4 to 5% for scroll but basically no oil remains in scroll crankcase.
Accumulator can hold 3 ounces of oil under some operating conditions.
hotrodac (MACS Trainer License #115)

ice-n-tropics, Thanks for the reply and nice to meet you. You seem well regarded around these parts!

Thanks for mentioning the OCR (see below "Fun with numbers")...took me a few rounds to really get that.

In general, seems that without the variable condition sampling and testing its impossible for the DIYer to know what's happening.

This is where field expertise like bohica2xo providing similar systems becomes so valuable.

In the examples provided going with 25% of oil volume as refrigerant weight seems like a good approach. (Do the two weigh the same since we are comparing oil volume to refrigerant weight?....and does it matter?) Thankfully the system examples bohica2xo gave use the same compressor and similar system sizing.

It would be nice to be able to fill with a combined oil+refrigerant material but it seems like the oil will have to be put in periodically and pre-emptively because if optimal charge is reached before oil is added adding the oil may bring it over capacity.

___________

Sanden manual Section 10.4.2 In Laboratory Oil Amount Determination (OCR)

• While the vehicle A/C is operating refrigerant samples are pulled from the liquid
refrigerant line at several operating conditions. These samples are weighed then the
refrigerant is evaporated from the sample leaving oil which is weighed again. Dividing
the mass of the oil by the mass of the refrigerant plus oil will yield a ratio at the
conditions the sample was taken. This measurement is referred to as the Oil
Circulation Ratio or OCR.

_____

Ratio vs percentage, and it can make a difference!

Turns out there is no standard definition! (google it, interesting readin’)

The Sanden manual uses #2 as “OCR”atio

The MACS article never calls it OCR but they use #1 for their “25% rule” and examples. And then as an added complication bonus!, MACS goes on to saying that many times the 25% rule doesn’t apply!

1) One compares the count of something to the count of some other thing.

There are 2 females to every 6 males – there is 2oz oil to every 10oz of refrigerant 2:10 = 2/10 = .20 = 20%

2) The other compares the count of something to the count of everything.

There are 2 females from 8 people [2 females and 6 males] – there is 2oz oil to 12oz total capacity [2oz oil +10oz refrigerant]) 2:12 really isn’t used in this example but the following are 2/12 = .1666 – 16.6%

I’ve always thought #1 as ratio and #2 as percentage…guess not always so outside my world

Fun with numbers

1) 25:100 = 25 oil : 100 refrigerant = 25/100 = .25 = 25%....or “5%” more than #2 but in fact 5/20 so 25% more than #2

2) 25/125 = 25 oil / 125 oil+refrigerant = .20 = 20% …..or “5%” less than # 1 but in fact 5/25 so 20% less than #1

16 Oz of R134a by weight is 12.09 fluid Oz

The FS 10 depends on the refrigerant flow for lubrication. Unlike the Sanden, it retains very little oil inside.

bohica2xo wrote: ↑Thu Oct 19, 2023 10:49 pm 16 Oz of R134a by weight is 12.09 fluid Oz

Thanks helpful!

The terminology fl of vs weight oz doesn't seem to me consistent. Like the MACS article uses fl oz of oil and ratios it to weight of refrigerant. The Sanden ORC calculation uses only weight.

Since in oil 1 fl oz weighs about .94 oz maybe its close enough for AC work. (different oils are slightly different, I don't have a hard number on PAG oil)

The weight vs volume info above will be helpful in estimating the OCR with the higher volume receiver. I'll have to re-do my calculations. The RedDOT link above references lbs of refrigerant per ft of hose so that is already in weight and doesn't have to be converted from refrigerant volume.

And all in all, the example systems bohica2xo provided are likely the place to start. For my OCD mind however, its nice to figure out the logic behind the curtain as verification.