Automotive Air Conditioning Information Forum (Archives)

Airstream on Thu July 14, 2011 1:13 PM

Year: 1984
Make: Chevrolet
Model: Suburban C-20
Engine Size: 454
Refrigerant Type: R134a

I got my '84 Suburban C20 (454, dual-air, R134a, CCOT, A6 compressor) out of the shop the day before leaving on a trip, and the conditioned air was not as cold as it has been in the past (while using R134a).

While returning from the six-hour trip in 90 deg weather, none of us were comfortable.

For a variety of reasons, I suspect there may be too much oil in the system, and need a plan if I decide to address the issue myself.

In Googling ways to determine if the system has too much oil, I ran across what appeared to be a page out of a GM manual which, among other things, said, "...on A-6 compressor, if amount of oil drained is 8 oz. or more, an oil overcharge should be suspected."

Since an A-6 has a drain plug, this seems like a pretty fast check. If the compressor does have 8 oz. or more of oil, then it would then make sense to remove & drain the accumulator since it looks like it can hold a serious amount of oil.

I'd appreciate any comments anyone has on the above approach.

Tom

Cussboy on Thu July 14, 2011 2:57 PM

Your first post: but I know that you know to recover the refrigerant first, and to wear eye protection.

Cussboy on Thu July 14, 2011 2:57 PM

Edited: Thu July 14, 2011 at 2:59 PM by Cussboy

HECAT on Thu July 14, 2011 3:22 PM

For a variety of reasons? Verify refrigerant charge, heat exchanger air flow paths, and post pressures and vents temps.

As far as oil overcharge; the real issue is how much is in there. So you use this GM method to determine you do indeed have too much in there; so what formula will you then use to calculate how much to remove? The only way to know for sure is to start with a clean and dry system and add the correct amount oil.

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HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

Edited: Thu July 14, 2011 at 3:23 PM by HECAT

Airstream on Thu July 14, 2011 4:38 PM

Quote
Originally posted by: HECAT
For a variety of reasons? Verify refrigerant charge, heat exchanger air flow paths, and post pressures and vents temps..
The shop I got the truck back from tells me they did all of that except vent temps. Anyone could tell the vent temps were did not reflect the low side reading.

Keep in mind I'm doing my homework first before anything.

I like the man who did the work, and feel sure he loaded the correct amount of refrigerant, and that the gauge pressures are probably going to read like the vents should be blowing 50 degree air out. But they are not.

Another part of the problem is that the Internet starts with the oil capacity of later year Suburbans. If anyone knows the correct oil charge for my truck, I'd appreciate hearing what it is.

My preference is to let a well-equipped shop who wants to make this right do the work. But I'm having trouble locating one.

Tom

Edited: Thu July 14, 2011 at 4:51 PM by Airstream

HECAT on Fri July 15, 2011 11:18 AM

My first find on system capacities were 84 oz of R-12 and 10 oz of oil (with the A-6 compressor). I would need to confirm this with the sticker under the hood, or a second source. Maybe someone else can confirm.

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HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

TRB on Fri July 15, 2011 12:37 PM

Quote
Originally posted by: HECAT
My first find on system capacities were 84 oz of R-12 and 10 oz of oil (with the A-6 compressor). I would need to confirm this with the sticker under the hood, or a second source. Maybe someone else can confirm.

Should be pretty close for a F & R setup.



-------------------------
When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

Airstream on Fri July 15, 2011 4:59 PM

Thanks HECAT & TRB. Unfortunately, there is no under-hood sticker for some reason. Strange because I'm the second owner of the truck, and the original owner was not the type to remove stickers.

I hope someone else will confirm what the two of you suggest for two reasons:
1) The Chilton's guide to AC repair & service for '82 - '85 I have declares 16 oz oil for 'conventional' (with A-6), and 19 oz oil for 'overhead'. Both entries (especially the 19 oz one) struck me as a lot of oil. The R-4 compressor is apparently only used with dash-only air, and Chilton listed 12 oz for it. That too strikes me as lotsa oil.
2) NAPA's online guide starts with '86 Suburbans. They suggest 9 oz oil for dual-air. AutoZone's site tells me that truck also uses an A-6 compressor. '84 & '86 Burbs are really only distinguishable by the front grille. Are y'all aware of some dramatic difference in A/C components?

The more I read & think, the more my head hurts. I originally thought the low-side accumulator is there to accumulate refrigerant like the receiver-dryer does when installed in the high-side of other models. Now I think the CCOT system accumulator's purpose is to collect oil because its usable space only sees refrigerant vapor, and the J-tube appears to be designed to mist oil into the vapor headed towards the compressor.

Tom

JJM on Sat July 16, 2011 12:41 PM

I'm showing 6 oz for an R-4 and 10 oz for an A-6 on this vehicle, with no differentiation between front and rear air. The only differentiation I see between front and rear air is 48 oz of R-12 for front only and 85.25 oz of R-12 for front and rear (gosh I love these trucks).

Joe

When considering your next auto A/C purchase, please consider the site that supports you: www.ACKits.com

iceman2555 on Sat July 16, 2011 5:43 PM

First and foremost it is necessary for the system be fully charged prior to any performance diagnosis....anything else and all becomes a simple 'guess-ta-mation'. Pressures are not an indication of a fully charged system. Pressures are an operational tool for diagnosis of a fully charged system. The statement that the system the tech (?) 'surely loaded' the system with the correct amount is asinine. How was the charge amount determined? A small wager of $.01 will suffice to say.....PRESSURES. When retro fitting a system...pressures are out the window.....the 12 system components were never designed to operate with the pressure/temperature requirements of 134a.
Why or what happened to the system to make one think there is too much lube in the system? Excessive lube will normally generate excessive liquid line pressures.
Inquire with the tech to determine how much lube was added to the system. Were components replaced? Was the system flushed? What type flush was used? Was the compressor drained and recharged with the correct lubricant? Tell us more about what happened and why.
There are serious assumptions in this post.....lets get down to the 'nitty-gritty' and solve this cooling performance issue.


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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

Airstream on Fri July 22, 2011 9:17 AM

Well, my truck's system does not have too much oil in it now.



I started another thread on my Suburban's lack of cooling if you want to read what happened.

Tom

Airstream on Mon July 25, 2011 7:55 AM

I spoke too soon. Between the hose blowout, and what I could not catch during the teardown, I figure I didn’t recover 3 or 4 ounces of refrigerant oil. But here’s the 16 ounces I was able to recover:



If you look closely at the smaller cup, you’ll notice the oil has separated. I’m assuming that’s mineral oil on the top, and R134a-compatible oil on the bottom.

It appears that my trust in Danny, the technician who did the last “repair” on the Suburban, was misplaced. He told me he was going to replace the expansion tube before recharging the system. Here’s what was pulled out:



I was able recover 68.2 ounces of R134a before taking everything apart. Everyone appears to agree this truck originally held 84 ounces of R12. 80% of 84 is 67.2 ounces of R134a. So, in spite of the gauge hose blowout, the Suburban still had an ounce of refrigerant too much.

It’s amazing the truck cooled at all.

Tom

bohica2xo on Mon July 25, 2011 3:39 PM

Wow. We will have to check with the board, but you are close to the record book for oil overcharge...

I figured 19 ounces of pag on top of the remaining 9 or so of mineral oil.

With all of that in the system you are very lucky you did not open something up while towing a load. That much oil on a hot exhaust manifold makes a heck of an engine fire. A blown hose or HPRV could have been very exciting.

what did you find in the screen at the rear TXV?

B.

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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Airstream on Mon July 25, 2011 4:32 PM

The rear TXV's screen was clean as a whistle, and nothing flushed out of the line.

The rear air handler was added later, and the rubber high-side line, to keep it away from the exhaust manifold, "drops" into the system. I figure gravity let all that crap continue on to the front air handler.

Tom

Airstream on Mon July 25, 2011 4:36 PM

Oh, and the compressor's inlet screen was clean, too.

Mr. SawzAll wants to aid in examining the old accumulator.

Tom

bohica2xo on Mon July 25, 2011 6:08 PM

Mr sawzall works, so does Mr pipe cutter.

If the screens were clean then that OT had not been changed. If you had made that much trash since the repair it would be everywhere.

Looks like you have a fairly straightforward repair from here. Pick the oil you plan to use, and buy enough to flush the compressor well before you add the oil charge.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Airstream on Mon July 25, 2011 8:12 PM

Mr. SawzAll just laughed, and reminded Mr. Tom that his pipe cutter only goes up to two-inch pipe.

Looking past the sprinkling of aluminum chips, you can see that the desiccant bags are dirty, and the bottom of the accumulator looks like water sat there for a while:





No clumps on the pickup screen, though.

Tom

Edited: Mon July 25, 2011 at 8:15 PM by Airstream

JJM on Mon July 25, 2011 10:57 PM

Wow, no wonder the system wasn't cooling! That's a whole lot of oil.

It's also bordering on criminal that a $2 OT wasn't replaced and obviously not inspected.

Something tells me that when you're done, that Suburban could be used as an auxillary freezer.

Also, for the retro, make sure to use a Ford blue OT (0.067) and turn your CPS cutout pressure down to around 19-21 PSI for R-134a.

Joe

When considering your next auto A/C purchase, please consider the site that supports you: www.ACKits.com

Airstream on Fri July 29, 2011 7:47 PM

A couple of days ago, I got an email from a friend who told me he had just bought a 1958 Airstream whale-tail, and subsequently ask what was going on here in Alabama. Although I have no reason to think Hugh knows that much about MVAC, among other things, I shared a link to this particular thread about my A/C woes just because the Suburban's A/C has taken up a lot of my time lately.

I enjoyed his response. Maybe you will too:

Quote
...Reading about your AC ordeal was like reading a high drama murder mystery. It didn't take long before you were able to identify the primary suspect, (who turned out to be quite a villain), but then began the sticky problems of trying to determine all the crimes he had committed, how they were carried out, and what you must do in order to establish the facts and make your case. Before I finished reading all the posts, which were loaded with assorted ideas, suggestions, and advice from innocent bystanders, plus the lament of others, who, at some time in their distant past, had been the victim of similar crimes, my head had begun to throb. Realizing that I was trying to solve the puzzle before I had all the facts, I treated my pain with a couple of bottles of ice-cold beer, then was able to read on until I felt that you had solved the mystery. I hope that by now, the "Burb" will cool down to the point where you could use the entire unit as a gigantic beer cooler on wheels, without ice, should the need arise...

Tom

Edited: Fri July 29, 2011 at 7:48 PM by Airstream