Drain oil out of new compressor?

[3b auto]

Hi guys I so glad I found this forum.
I do repairables hit in the front so Im learning AC, technically a newbie.
I bought a bunch of gear and currently doing a deep dive into a 2013 Passat that
has a persistant vacuum leak, Im heading out today to pickup a nitrogen tank after attempting
a YouTube fix using compressed air- didnt work and only added atmospheric air back into the system.

I only work on 2.5L VW so I bought extra parts to have in stock that includes a cheap knockoff compressor, air dryer, expansion valve, etc.

Ive been learning this industry from YouTube as a starting point.
My replacement compressor comes loaded with oil, some say drain and refill but Im not sure why? unless its low grade PAG just used for shipping?

*Also Im a bit mystified why you need to change vacuum pump oil with every use, seems excessive but granted i dont understand vacuum pumps.
In fact I vacuumed the Passat system x2 as part of my newbie learning curve attempting to find and fix the leak, last night I thought after using compressed air I better dry it again...my brand new pump only pulled -10, got very warm to the touch and I realized changing the internal oil every use might be more important than I realized. Hate to think I might have burned up a $200 vacuum pump but will try it again with fresh oil later tonight.

[Cusser]

My replacement compressor comes loaded with oil, some say drain and refill but Im not sure why?

I'm not an AC professional.

1. The oil in the replacement compressor might be of the incorrect type. In the early 2000s I once purchased a replacement compressor (from this board's sponsor) for my 1988 Mazda truck and that came filled with R134a type PAG oil, and I needed R-12 type 525 oil (I could check oil type at work in 3 minutes), so I had to do a flush then fill of compressor with the correct-type oil.
2. A month later, my co-worker bought same brand of compressor (from this board's sponsor) for his 1990 Mazda Protege, and that came filled with 525 mineral oil, which was correct for him as he was also staying R-12.
3. Last time I purchased a new compressor for that 1988 Mazda truck (again from this board's sponsor) was in 2014, and if I go by memory, I also had to flush out the PAG oil from that and fill with 525 mineral oil.

*Also Im a bit mystified why you need to change vacuum pump oil with every use, seems excessive

I use a vacuum pump from my past employer's lab, given to me because it was claimed to "smoke" but I'd use it in an open garage. Not only does it not smoke for me, but I haven't changed its oil ever in over 20 years. But I'm not an AC professional, use mostly on my own vehicles.

[3b auto]

Thanks that was helpful. I have no way to test whatever oil it shipped with.
Maybe thats why folks change it out to ensure the proper PAG

Not sure if mineral oil is still used in modern day R134A ?
I have 3 different viscosities of PAG

[Tim]

In general. Always drain the shipping oil and add back the vehicle spec and type.

This is what is stated now on the big 3 compressor dist listings, and is the standard policy for them.

OIL TYPE
CONTAINS OE COMPATIBLE OIL FOR SHIPPING; PLEASE REFER TO OE SPECIFICATIONS FOR OIL CAPACITY

[bohica2xo]

Draining, measuring and inspecting the drained shipping oil on a new compressor is absolutely needed.

I also suggest adding an ounce or two of the oil you intend to use in the new unit, and flushing it through the new compressor to make sure it has cleared the unknown oil
 

[JohnHere]

*Also Im a bit mystified why you need to change vacuum pump oil with every use, seems excessive but granted i dont understand vacuum pumps.

I change the oil after every second use. The oil does pick up moisture, so it's best to get the contaminated oil out so that the pump can draw the best possible vacuum. It's important to ensure that you use only vacuum pump oil as well.

...my brand new pump only pulled -10, got very warm to the touch and I realized changing the internal oil every use might be more important than I realized.

Do you mean it pulled the system down to only 10 InHg? If so, it's unlikely that your new vacuum pump is defective, although anything is possible. Change the oil in your vacuum pump and try again. If you still see only 10 InHg or thereabouts, either the system has a large leak or your equipment isn't holding vacuum.

[Cusser]

Thanks that was helpful. I have no way to test whatever oil it shipped with.
Maybe thats why folks change it out to ensure the proper PAG

Not sure if mineral oil is still used in modern day R134A ?

No - mineral oil is not used with R134a, not compatible.

[bohica2xo]

Regarding The oil changes on vacuum pumps, A lot depends on what you are sucking up with your pump. But moisture eventually fouls the oil.

Small, direct drive pumps don't hold much oil. So it gets contaminated fast, but it is not bad to change.

For reference I believe Cusser is using a lab pump like a Welch Duo Seal. They hold Quarts of oil. I have a 1402 Welch. In a lab as a roughing pump, weekly oil changes can be necessary. The link below is the manual for the lab pumps. It describes in detail what goes wrong with pump oil and the result:

https://www.lesker.com/newweb/vacuum_pu ... manual.pdf

3.102 Oil Contamination
The most common cause of a loss in efficiency in a mechanical pump is contamination of oil. It is caused by
condensation of vapors and by foreign particles. The undesirable condensate emulsifies with the oil which is
recirculated and subject to re-evaporation during the normal cycle of pump activity this reducing the ultimate
vacuum attainable

.

[Cusser]

For reference I believe Cusser is using a lab pump like a Welch Duo Seal.

Yes. I have a Cenco Hyvac2, capacity is listed as 1 qt. oil.