Open Road

I bought a used compressor from 928 International to swap in my car. The old compressors front seal blew out and all thw refrigerant drained out.

The used compressor is in good shape but I want clean oil in it.

What's the best oil to use and how do I drain the old oil out?

You think the used compressor isn't going to leak refrigerant?

Or, I guess you're prepared to put a can or three of r134 in it every year.

Fine.

I assume you are using r134a since use of r12 in CA carries the death penalty or something worse. Directions are materially different if you are not using r134a.

Remove the service manifolds. Drain the oil in the compressor. You'll want to rotate the pulley (in the proper direction) while you're draining to get as much out as you can. You can let it drip for hours if you want to. You'll want to cobble-together a jig to hold it upside down over a catch pan for this.

Your converted-to-r134a system is - most probably - using A/C Ester Oil. This is what you want to use. Ester Oil. Not mineral oil. Not PAG oil. Not double-end-capped PAG Oil. Ester oil. Ester oil will be compatible with whatever residual oil is in your system and the compressor.

The compressor is probably full of either Mineral Oil or Ester Oil. The chances of it being filled with a non-compatible oil are very low.

The tricky part is estimating how much oil was expelled from the system as the result of your compressor's unscheduled self-discharge. The 928 is properly filled with 8 ounces of refrigerant oil. If the compressor you bought is the proper Denso 6E171 as originally equipped, it will run fine on as little as two ounces in it. However, if you lost most of the oil in the rest of the system, two ounces in the compressor will get distributed to the rest of the system and your new used compressor will seize.

However if you put 8 ounces in the compressor, you will have over-oiled the system and it won't cool. In a situation like this 4 ounces is probably a reasonable guess. (What you are actually supposed to do is to flush the system to remove all the old oil (and crap) after which you'd put in 8 ounces.)

Add the oil into the compressor and reinstall the service manifolds with new o-rings.

It's not yet converted actually. It does hold vacuum though which is good news. Either way I'm putting a new drier and expansion valve in it and will likely flush the system before installing the 'new' (used) compressor. This will also include replacing whatever o-rings I can get to (including rear AC) before filling up with r134a (if I convert.)

I assume there is no more r12 left in the states or vendors on the forums. That said, if I can get my hands on r12 still then I will keep it an r12 system.

Screw CA. MOLON LABE

Mongo wrote: ↑Mon Jul 07, 2025 9:58 am ... will likely flush the system before installing the 'new' (used) compressor.

If you are using an A/C machine for the flush then you don't have to drain the compressor I suppose.

If you are flushing component-by-component in situ "by hand" then flush the compressor before you bolt the service manifolds back on.

Mongo wrote: ↑Mon Jul 07, 2025 9:58 am This will also include replacing whatever o-rings I can get to (including rear AC) before filling up with r134a (if I convert.)

Mineral Oil for r12. Ester oil for r134a. No other options for r134a unless you get every last molecule of mineral oil out.

After a good flush you can put 6 to 8 ounces of oil in. In this case 6 or 7 is better than 8.

You are also supposed to change all the rubber hoses to barrier-type when you convert. But, other than the compressor lines, it's a major effort and expense.

Mongo wrote: ↑Mon Jul 07, 2025 9:58 am I assume there is no more r12 left in the states or vendors on the forums. That said, if I can get my hands on r12 still then I will keep it an r12 system.

Look on ebay for folks that still have the 12oz-16oz cans. Expect to pay $$$ per pound.

Thanks worf. I'm also going to check craigslist and offer up in case I get lucky there too with R12.