Correct way to recharge AC 72 Duster 340 with Sanden 508 compressor

[HSDemon]

This is a Factory AC car, that at some point got converted to R134 and a Sanden 508 compressor was added to it. When I bought this car the AC was not working, and it was easy to see why. One of the hoses going from the compressor to the firewall had failed at the crimp on one of the end fittings, so it would not hold refrigerant. Not having the correct AC tools to crimp AC hoses, I just took the hose to a local AC shop and they made me a new one.

I am by no means an AC guy, my AC experience comes from removing them from most previous vehicles I had: "because race car"... Anyways, I have the AC gauges, the vacuum pump, oil injector, I have an AC flush kit, I have ester oil with dye, I bought a new drier and expansion valve and I am ready to put this back together and charge it. My concern is that when I took out the hose the oil that was in there was pretty black. I don't know how much oil was in that hose, so I have no idea how much oil was lost from the system, but I suspect that there wasn't much. I assume that there is some oil in the drier too, so when I change it I should add a bit for that.

From what I have been able to find, a Sanden 508 uses 6 ounces of oil when new with an AC system that has no oil. If I just removed that hose, the drier, and the expansion valve maybe add 1/2 of an ounce of oil? The old oil is kind of dirty and I am unsure if I should just flush the whole thing and put new oil. This AC compressor was added to the car about 20 years ago, but I doubt that it was used much. I would very much like to see what the AC guys here suggest I do.

 

[Darter6]

Concerned about the black oil. Flush the system. Remove the compressor and dump and flush as best as you can.
When flushing remove the expansion valve and dryer and flush the remaining evap and condenser .
You stated you have those parts new.Then use fresh oil in the compressor, about 3 oz. Use the remaining 3 in the
lines going to the condenser. Pump the system down for about 1/2 hour and test to see if it holds vacuum.With a new dryer
1/2 hour is fine.
10-15 minutes if no vacuum loss you should be good to go with freon.Try 1 can(if you are using cans) Usually 1 will be enough
to trip the binary switch and run the compressor. After a few minutes shut it down and check for leaks at all fittings.
If all good top off the freon.

 

[Demonic]

If you had a friend who does commercial AC you could pressurize it with nitrogen to 150 psi and let it sit for a day, should be no pressure drop unless ambient temp takes a swing.

Ester oil w dye is good. It's compatible with any minor trace of mineral oil AND 134a. I'd pull the compressor and dump the oil, add 6 oz new Ester and maybe a 1/2 oz. Like Darter said, black oil is not good, sounds like it got oxidized or the system was open for a long time. Oil pools in low spots when velocity is low or the oil is cold. When the load is high w high condensing temps, the oil will make it's way back to the compressor.

 

[HSDemon]

I guess the right thing to do is to pull the compressor and clean everything out. It never gets easy...

 

[67Dart273]

I would not re-use the hoses nor receiver dryer. Flush the evap and compressor and make certain you get all old oil out. I guess what I'd do is use trichlorethylene same stuff in brake clean, then flush with R-134

If you need pressure for the trich, I'd use CO2 or nitrogen, then blow both out with only the CO2 or nitrogen, then waste a can each of 134 for the evap and the compressor

Immediately seal it up and evacuate, then purge with yet another can of 134. You can purge into the high side fitting when under a vacuum, the 134 will travel through the hoses, evap, and back around to the compressor. Add nitrogen or CO2 as necessary to pressure test, then evacuate once more and re charge.

Many guys have argued with me on this, but a great way to get the new charge started with less fuss, and completely safe, is to start with the evacuated system, dump LIQUID refrigerant into the HIGH side fitting. By the time it is around the backside to the compressor, it will have flashed to vapor

Do what you can to keep the evap warm when evacuating and starting to charge. Do this on a warm day, and use the heater if necessary to get the interior up to at least 80F

Also when evacuating it is a good idea to warm up the engine and engine bay. Keeping the AC system warm will help to vaporize any remaining moisture and carry it off with the evac

 

[RustyRatRod]

I would not re-use the hoses nor receiver dryer. Flush the evap and compressor and make certain you get all old oil out. I guess what I'd do is use trichlorethylene same stuff in brake clean, then flush with R-134

If you need pressure for the trich, I'd use CO2 or nitrogen, then blow both out with only the CO2 or nitrogen, then waste a can each of 134 for the evap and the compressor

Immediately seal it up and evacuate, then purge with yet another can of 134. You can purge into the high side fitting when under a vacuum, the 134 will travel through the hoses, evap, and back around to the compressor. Add nitrogen or CO2 as necessary to pressure test, then evacuate once more and re charge.

Many guys have argued with me on this, but a great way to get the new charge started with less fuss, and completely safe, is to start with the evacuated system, dump LIQUID refrigerant into the HIGH side fitting. By the time it is around the backside to the compressor, it will have flashed to vapor

Do what you can to keep the evap warm when evacuating and starting to charge. Do this on a warm day, and use the heater if necessary to get the interior up to at least 80F

Also when evacuating it is a good idea to warm up the engine and engine bay. Keeping the AC system warm will help to vaporize any remaining moisture and carry it off with the evac

That's how I always do it now. Charge through the high side as a liquid. It works good and is usually a lot faster.

 

[Demonic]

With the price of refrigerant, I'd forgo using up any extra cans of 134. If you want to double evacuate, the standard commercial procedure is to break the vacuum with nitrogen, then pull a vacuum again. If there's any moisture in the system the first time, this can help dehydrate.

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[lemondana]

I just saw that R134 was 23.00 a can, I just bought 4 cans of R12 at our big swap meet for 15.00 a can, to add to my 80-90 lbs of R12 that I have. I will never use R134 in one of my old systems. I contacted Classic Auto Air a while back, asked them if I could use r12 in their new AC units-they said yes.