Oil Balance Question

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MeteorBurn
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Joined: Fri Aug 14, 2020 7:29 am

Oil Balance Question

Postby MeteorBurn » Fri Aug 14, 2020 10:49 am

Hello everyone,

I've got a few questions concerning the A/C in my 1998 eclipse. I'm no stranger to working on cars, and I understand A/C is a tricky subject usually left to professionals but I figured with multiple older (90's) family cars that it wouldn't be a bad thing to try and learn.

The A/C has not been working for about 2 years and was empty. I found a few leaks (high and low side schrader valves, o-rings at the ends of the suction line) and repaired them.  When pulling a vacuum I accidentally shut off the pump before I closed the manifold valves on the gauge set and some oil (~ 1 oz) from
the pump was drawn into the system. I know, stupid error. I also think the pump I used (rental) had a defective backflow preventer. 

Long story short I removed the evaporator, compressor and lines. I put a solvent based flush through the evaporator after removing the expansion valve, and blew dried compressed air through it for a good amount of time. I drained the compressor, but I only was able to get about .2 oz of oil out of it. The lines were flushed and dried, and I am replacing the receiver dryer. 

1. I am essentially starting with a dry system. However, I don't believe the condenser took in any appreciable amount of vacuum pump oil. The service manual states that 1.35 oz of oil settles in the condenser, but since the system has been empty is that number accurate? The compressor barely had anything in it. I don't want to flush the condenser because I don't think I'll be able to get all the chemical out. It took a considerable amount of air to get just the evaporator dry. Should I assume there is 1.35 oz, or flushing it is the only way I can sure of the correct oil amount in the system? 

2. I'm finding conflicting information on installing the oil charge. Some manuals state to put the full charge in the compressor, some say put half in the compressor and the other half in the rest of the system. The system capacity is 2.7 - 4.1 oz. The manual uses 3.4 oz as the target amount. Would I be okay putting in 2.05 oz in the compressor directly and assuming there is 1.35 oz in the condenser? 

I greatly appreciate any advice. 
Al9
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Location: Southern Europe

Re: Oil Balance Question

Postby Al9 » Fri Aug 14, 2020 12:34 pm

As long as you're using an evaporative flush solvent, chasing it with a lot of dry compressed air (or even better OFN) and then doing a good vacuum you should be fine. Ideally speaking, a flush solvent has to be evaporative so that it's easily removed from the system.

If you flush the condenser too you can put all the system oil charge inside the compressor. If the compressor has an oil drain hole (or even better a dedicated oil fill hole) fill it in there, otherwise fill it in the suction port while you rotate the clutch hub. The most important thing is that you rotate the clutch 10 times by hand right after installing the compressor in the car and before turning the AC on. So that any excess oil will be pushed outside the compression chambers avoiding a serious oil slugging condition.

Some compressor manufacturers tell to distribute the system oil charge across different parts in the system mostly to favor oil return during the run-in phase.
IMHO i think that as long as the system is fully charged by weight with the compressor not running, and as long as the proper oil quantity, type (preferably double end capped PAG) and viscosity is used, and as long as the compressor is correctly ran in (right after engaging the AC for the first time, keep the engine at idle, the blower at maximum speed and fresh air, that is air drawn from outside, set for a few minutes straight while the AC is on; the idle engine keeps wear at a minimum and the fresh air and max speed blower keeps the evaporator from getting too cold/a TXV from closing too much, maximizing oil circulation rate and returning all discharged oil back to the compressor), it won't be a problem.

The only time distributing the system oil charge across the system is really necessary is when the system has an accumulator. Filling it with a few ounces of oil will provide a steady supply of oil during the first few compressor shaft revolutions, otherwise the evaporator will have to output enough oil before it will begin returning it to the comp and it may run dry for too much.
But your system has a TXV and all oil flowing out of the evaporator will go straight to the compressor so you shouldn't worry.

In fact that's all i've instructed a shop to do a few days ago when i got a new compressor fitted and it's running quietly and perfectly.
MeteorBurn
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Joined: Fri Aug 14, 2020 7:29 am

Re: Oil Balance Question

Postby MeteorBurn » Sat Aug 15, 2020 11:39 am

Thanks for the help. I'm almost finished with getting the condenser out. Evaporator has been reinstalled under the dash.

One other question I have is about the factory specification for the refrigerant amount. The sticker under the hood says 23 oz, while the service manual states the capacity as 24.69-26.10. Would I be okay putting in two 12 oz cans, or should I try to keep the last ounce in one of the cans and put in exactly 23 oz?
Al9
Posts: 203
Joined: Tue Mar 10, 2020 3:26 am
Location: Southern Europe

Re: Oil Balance Question

Postby Al9 » Sat Aug 15, 2020 12:01 pm

My advice is to take the car to a shop equipped with the appropriate equipment. Cans are shadow tree-ish and inaccurate and the proper refrigerant charge amount being there right as the compressor shaft starts turning is crucial to minimize wear during a compressor run-in procedure (=anytime you add a relevant oil charge to the system).

And i'd follow the sticker. Who knows what model year a manual might be referring to.
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Cusser
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Re: Oil Balance Question

Postby Cusser » Sat Aug 15, 2020 4:00 pm

MeteorBurn wrote:Thanks for the help. I'm almost finished with getting the condenser out. Evaporator has been reinstalled under the dash.

One other question I have is about the factory specification for the refrigerant amount. The sticker under the hood says 23 oz, while the service manual states the capacity as 24.69-26.10. Would I be okay putting in two 12 oz cans, or should I try to keep the last ounce in one of the cans and put in exactly 23 oz?


You'll never get full 12 oz. from a 12 oz. can.
1. You need to purge the hose.
2. Some remains in can.
GM Tech
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Joined: Fri Apr 22, 2016 7:22 am

Re: Oil Balance Question

Postby GM Tech » Sun Aug 16, 2020 1:43 am

If it makes you feel any better- just know that absolutely every automotive compressor built was installed in its vehicle home with the entire system charge amount of oil in its belly! So I'm not a big fan of oil distribution upon repairs. I worked for Delphi for 30 years and have been in every N. American assembly plants watching the a/c evac and fill- and you can be assured it is this way. So, it matters very little, where you put the oil- just make sure the pump has plenty.
Al9
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Location: Southern Europe

Re: Oil Balance Question

Postby Al9 » Sun Aug 16, 2020 1:54 am

Entirely true - in fact this is what my shop did a few days ago with my brand new CVC comp. Flushed system, 5 oz of oil straight into the drain hole, nose down for a minute, clutch hub turned 10 times by hand, then charged it up and fired it up.

Purring like a kitten at idle now (noisy when revved only thanks to the wrong - red instead of blue - control valve).
MeteorBurn
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Joined: Fri Aug 14, 2020 7:29 am

Re: Oil Balance Question

Postby MeteorBurn » Mon Aug 24, 2020 7:19 pm

Just a little update, flushed out the condenser and put plenty of compressed air through it. I used Dura flush II, that stuff evaporated scary fast. Not sure why there weren't any flammability warnings on the can.

Put the oil charge into the compressor, spun the clutch 10 times, and reattached everything else taken off. I wasn't too worried about break in because I wasn't replacing the compressor - nothing wrong with the old one.
One pipe connection on the condenser was pretty much frozen together, and I wasn't willing to heat it up/drill a small hole in the nut, so I left it alone. It's the only o-ring that didn't get replaced, lol.

I then pulled a vacuum for 3 hours just to make sure everything was good. Held vacuum for about 4 hours with no drop. The oil in the vacuum pump got pretty milky after an hour of running so it definitely pulled a good amount of moisture (I changed it before running it again). Rethought my strategy of charging the system with cans and just decided to have a shop do it - it was cheap enough anyways, and I let them know that I put a full oil charge in the system and no additional oil was needed, no problem. I didn't want to take the risk of overcharging or undercharging and making more problems.

Cooling very nicely now. Following the load test from the service manual (windows closed, recirculation mode, max fan speed, front vents only) I got about 49 degrees from the center vents. Temperature in the garage was 85 F with 70% humidity. Does that sound respectable? The thermometer was actually still dropping, it just became very slow. The manual was not very helpful in this regard because it only lists two ambient temperatures, 75 and 95 degrees with no humidity levels mentioned (39 - 46 F being acceptable vent temps). Ironically the manual for another car in my fleet, a 1995 oldsmobile cutlass, lists up to 62 F discharge temps as acceptable at that temperature and humidity.

Anyways, thanks for the help. As an HVAC controls technician I definitely appreciate the complexity of mobile A/C systems much more now.
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Cusser
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Re: Oil Balance Question

Postby Cusser » Mon Aug 24, 2020 8:27 pm

Should get even cooler with actual driving !!! Try that !
Al9
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Location: Southern Europe

Re: Oil Balance Question

Postby Al9 » Tue Aug 25, 2020 1:43 am

You're welcome. Glad to know everything's fine.

About the 49F vent temperature, if you have the Mitsu scroll unfortunately that's a little quirk of scroll compressors. You're likely at idle or low rpm and they're not that efficient at low rpms (and high evaporator superheats, a result of high heat loads and low rpms, too). As Cusser says you'll get better performance down on the road.

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