Automotive Air Conditioning Information Forum

hmmm...if Bohica says it , it is

Digger:

Here is the spec sheet for that series of refrigeration oils. Scroll down for the chart

https://www.mobil.com/en/lubricants/for ... il-shc-525

.

Maverick:

That spectra part is a flat tube parallel condenser, and it does indeed have less volume. Some drop in units are 6mm Piccolo types, with a little more volume.

I am going to point you at the Mustang charge spec history. Scroll down to Mustang:

https://www.techchoiceparts.com/refrige ... ities/ford

In 1988, they were suggesting 10 ounces of oil. In 1989 they pulled that back to 8 ounces.

In 1994 when Ford went to 134a they used a serpentine condenser with reduced volume. It is larger on the outside, but has tiny passages.

In 1997 they were using a Piccolo type condenser, and a slightly larger evaporator. Note that the oil charge went up a little bit.

1988 and 1994 evaporator volumes are very similar. The big change was the condenser.

I would be inclined to drop back to the 8 ounce oil charge, and the 34 ounce refrigerant charge to start with, and see how the system acts when charged.

bohica2xo wrote: ↑Wed Jul 07, 2021 7:25 am Digger:

Here is the spec sheet for that series of refrigeration oils. Scroll down for the chart

https://www.mobil.com/en/lubricants/for ... il-shc-525

Thank you.

Unfortunately, the brochure does not include comparisons to mineral oil. The only mention of mineral oil is to state that their synthetic oils are superior to "comparable" mineral base oils.

I'll keep looking though, curiosity.

bohica2xo wrote: ↑Wed Jul 07, 2021 7:37 am Maverick:

That spectra part is a flat tube parallel condenser, and it does indeed have less volume. Some drop in units are 6mm Piccolo types, with a little more volume.

I am going to point you at the Mustang charge spec history. Scroll down to Mustang:

https://www.techchoiceparts.com/refrige ... ities/ford

In 1988, they were suggesting 10 ounces of oil. In 1989 they pulled that back to 8 ounces.

In 1994 when Ford went to 134a they used a serpentine condenser with reduced volume. It is larger on the outside, but has tiny passages.

In 1997 they were using a Piccolo type condenser, and a slightly larger evaporator. Note that the oil charge went up a little bit.

1988 and 1994 evaporator volumes are very similar. The big change was the condenser.

I would be inclined to drop back to the 8 ounce oil charge, and the 34 ounce refrigerant charge to start with, and see how the system acts when charged.

Thanks for explaining the probable reasons for the amount of oil to use differences. That they are due to equipment/system volume differences

Sorry digger, grabbed the wron sheet this morning before coffee.

525 refers to SUS viscosity, which in ISO would be around 100.

bohica2xo wrote: ↑Wed Jul 07, 2021 7:37 am
I would be inclined to drop back to the 8 ounce oil charge, and the 34 ounce refrigerant charge to start with, and see how the system acts when charged.

Thank you. That was very helpful and i completely understand the logic of how you arrived at those numbers. Makes sense to me.

bohica2xo wrote: ↑Wed Jul 07, 2021 9:04 am Sorry digger, grabbed the wron sheet this morning before coffee.

525 refers to SUS viscosity, which in ISO would be around 100.

Bingo! A new search term that includes SUS.

bohica2xo wrote: ↑Wed Jul 07, 2021 7:37 am

I would be inclined to drop back to the 8 ounce oil charge, and the 34 ounce refrigerant charge to start with, and see how the system acts when charged.

So, a year later and I can report that the system is complete, charged and it's been working great for a few months now. Granted, we are just now starting to get into summer, but i've done a few drives with nice cold AC and am a happy guy.

I ended up doing 34 ounces of R12 and 8 oz of oil and the system seemed to work great. On a nice hot/humid day, i had vents temps right around 40 degrees, so I just stopped there and closed everything up.

In the back of my mind, i've always wanted to validate that the pressures are where they need to be by comparing to a chart, or a rule of thumb, or something just to confirm that everything is good. I used a refrigerant scale to charge, but just want some validation.

What sort of pressures should I be seeing depending on various ambient conditions? It's tough to search for this info as vast majority of info these days is R134a based. Again, not looking to touch anything on the system, but just want to confirm that everything looks to be as it should.

Good work, glad it worked out and that you reported back, which seldom happens.
Most of us do not like to be handcuffed by a printed chart of pressures.
If you are getting 40° vent temps, you must have done something right.

Why not post the pressures you have on an 80+ degree day, max fan, max cool, recirc, doors open, at 1500 RPM and let us take a look see. Provide the ambient.

Given that you are using the precious R12, I would add that a good investment would be an electronic sniffer, and I would sniff the system every once in a while to head bad things off. But that may just be me. I would be lost without my sniffer