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1998 Tahoe w/dual AC

Hardrock on Thu August 18, 2011 10:25 PM User is offline

Year: 1998
Make: Chevtolet
Model: Tahoe
Engine Size: 5.7 350
Refrigerant Type: 134a
Country of Origin: United States

Hi folks!
Recently bought a 1998 Tahoe with non-working AC. 157,000 mi. History unknown. It appears to have the original accumulator and compressor on it, according to the stickers. Everything looks clean and dry with no obvious signs of leakage anywhere.
Virtually no charge in the system by thumbnailing the schrader valve.( Faint hiss.)
First thing I checked was the OT. It had the normal medium greyish film of a high mile system, but no debris present in the screen.

This is going to be a keeper for the wife, so I decided not to cut any corners with a re-man compressor, and I knew the OEM H6 was a lost cause even when new. So.....
After a lot of research and hunting around, I finally settled on an aftermarket kit with a new revised design compressor, accumulator, OT, and green O-ring package. I sourced a new OEM style replacement condenser and plan on flushing both evaporators and the hard lines with approved flush through a flush gun. I'll clear the manifold with shop air. I don't plan on running any flush through the rear expansion valve, just inspect it and replace it if in doubt.

Everything is getting assembled with Nylog, and I'm borrowing a vacuum pump to test for leaks before I take it to the AC shop for a complete charge.

Here's where I hit a stump......with all the repackaging, relabeling, no labeling, etc. How do you determine what oil to put in the system?
I know the compressor manufacturer specs PAG 150 for this application, as does GM, but I would prefer to use "double end capped" PAG 150 due to the improved moisture resistance.
Nobody local has ever heard of it. The monkeys at the parts houses just give me a blank stare. They all carry PAG 150, but the labels tell absolutely nothing about the molecular structure of the oil. Ultra, Super, Premium, Uncle Ben's Famous Recipe.......who knows?
They just hand me a bottle and say "This is what everybody else is using." Er, well, "everybody else" probably just accepts the fact that they have to fix their AC system every other year.....................Not what I'm looking for.
One guy told me ALL PAG is now double end capped PAG and nobody even carries the old stuff anymore. Hard to believe......
A few of the brands labeled "Premium PAG 150" are actually DEC PAG, but you have to REALLY research online to know that.
Others differentiate from "Standard" PAG, but tell little else.
The only thing available locally that looks halfway promising is a product called Quest PAG 150 made by E F Products out of TX.
What is it?? PAG or DEC PAG?

I really hate to order and wait, so anyone know what brands to look for locally that are DEC PAG oil, but maybe just not labeled as such?
Also, my system calls for 11 oz. (w/dual air) I'm going to add 9 oz. distributed throughout the system, and leave room for my AC guy to inject the remaining 2 oz. with UV dye when he pulls it down to charge it. That sound OK? Is UV dye a good thing or a bad thing?

Thanks! Mike

Stresst on Thu August 18, 2011 11:07 PM User is offline

Sorry cannot answer your question but :

Please do me a favor, please look at the sticker under the hood and post what the capacity is. Just curious to see what it is.

2000 Cadillac Escalade w/rear air

mk378 on Thu August 18, 2011 11:12 PM User is offline

This site sponsor sells a DEC PAG with UV dye already added. UV dye is good insurance to help find any leaks in the future, it doesn't hurt anything to just leave it in.

If you have access to a vacuum pump, there's little reason not to just charge it yourself. Using a 30 lb cylinder and a scale would be best on a large system such as this. With a major rebuild, conduct a pressure test before committing to a full charge.

Hardrock on Thu August 18, 2011 11:46 PM User is offline

Hi Stresst!

My factory 1998 label states...... R-134a

Suburban 3 lbs. 8 ozs. (1.58 kg)

Yukon/Tahoe 2 lbs. 12 ozs. (1.247 kg)

use synthetic oil #12345923 or equiv.

Obviously, 'Burbs are longer wheelbase, longer rear lines, larger capacity.
'Hoes/Yuk's/'Lades, w/rear AC should all be the same capacity. AFAIK

That should hold true for any of the Vortec equipped Escalades with the old body style that had the Harrison H6. (96-2000)
When searching for capacities, remember there were two different body styles/compressor options in 2000. One was the Vortec trucks with the H6 (old body style), the other was the LS (LQ-4, LQ-9 actually) engined, (new body style) trucks with a later style compressor.
Hope that helps...

Hardrock on Fri August 19, 2011 1:55 AM User is offline

Hi mk378,

I've been a leisure time mechanic off and on for 35+ years and always shyed away from AC work.
Not really because of the aggravation associated with trying to un-do the other guys "fixes",
but mainly because of the equipment costs and room to store it all.

I've got 4 more completes after this one, and they're all R-12 to R-134a conversions except my '96 Tahoe. It's basically the same scenario as the wife's '98.
I'm finding it's better for me to do all the labor intensive $ work and have the AC shop handle the actual charge. He's done me real good on alignments and stuff in the past, and in this economy, I like to strike a balance between saving a little cash, and still patronizing the established businesses in town. We've all got to eat....
He's the only GOOD shop in town and he's the only one that charges from a digital scale AND does a minimum 60 min. drawdown on all his re-charges. The other shops just stick a wet finger in the air and watch the guages......LOL!

I don't know alot about MAC, (I'm learning!) but after talking to some of these local shops that claim to know, I now understand why alot of their customers are running around with their windows down the following summer.........

Anyway, I was just curious about the UV dye. I know it's standard procedure with newer GM vehicles from the factory, but just wondered if it was merely an acceptable tradeoff for easier leak detection.
My gut told me in a perfect world, the only thing that should be in the system is refrigerant and oil. So the dye stays in suspension and doesn't overburden the dessicant in the accumulator?
I know my AC guy said he doesn't put any in UNLESS it's a clean system. Meaning a "one time" shot and that "one shot" was all that was in the system.

I'll check out the DEC PAG on this site. I'm getting anxious for some ice cold AC......

GM Tech on Fri August 19, 2011 9:29 AM User is offline

Dye mixes in with the oil-- wherever the oil is- so is the dye--- Suspension -- yeah right , this guy have a crystal ball? Dye is absolutely harmless...

I pre-mix all my 1 gallon oil jugs and oil injectors bottles with that I never have to worry about it-- If I add oil- it gets the dye automatically...

This is a non-issue............

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

70monte on Fri August 19, 2011 7:05 PM User is offline

I also always use dye in my oil. Unless you flush out the rear portion of the system, putting the full 11oz will leave you with too much oil. On the 99 Suburban I worked on, I did not mess with the rear air portion and just added 8oz of oil because this is what the front systems without the rear portion call for as well as the trucks of this generation.

I wouldn't worry about using double end capped Pag150. When I totally redid the system on my 98 chevy truck four years ago, I just added the regular Pag 150 with dye and my AC still works great. I also just used regular Pag 150 five years ago when I converted one of my 92 Cavaliers over to R134a and the AC on it still works great.

I'm curious to see how well your tahoe cools with a charge of 3lbs 8oz since the 99 Sub I worked on last year called for 3lbs 8oz of R134a and I was only able to get vent temps in the high 50's. Last week I had to recharge it because one of the fittings came loose a little and most of the charge leaked out. This time I recharged with 4lbs which my factory GM service manual for my 98 called for and some other sources said and this time I was getting vent temps around 47 degrees with ambiant temps in the high 90's.

Also make sure your fan clutch is good. If its original it probably needs to be replaced.

Let us know how it turns out.


Hardrock on Fri August 19, 2011 10:41 PM User is offline

GM Tech,

Thanks, that makes me feel better about the dye. I was thinking something else not dyed oil.
I've been looking and reading too much! Probably somehow relating it to sealer.
Just too much "super fix all" stuff on the market to sort through............always tough to tell where the
line is between what works and what sells.
What probably had me concerned was, awhile back I helped a buddy repair a truck that was hit hard
enough to bust the coolers, and as we were tearing it down the condenser and lines
were dripping green crap. Looked alot like Slime for ATV tires, only thinner.
He called it dye. Must have stuck in my head.......
I know now, it was most likely some kind of leak stop.


Yes, I'm flushing the whole thing, front and rear. Really want to know for sure what the entire system contains as far as oil.
As far as I can tell, there was no earth shattering failure here, just high miles and a leak somewhere.
Pretty sure all the oil will show some traces of the grey stuff that the OT saw. I figure start fresh and know exactly what it has in it.

As far as the 2 lbs. 12 oz. charge..........I dunno. That's just what the tag showed. I had other quotes at 64 oz. 56 oz. as well as the 44 oz. for a '98 Tahoe w/rear AC. I was kind of counting on the AC shops reference material for comparison.
Most likely start with the 44 oz. as per the GM label and see what we get. Next week looks fairly stable in the low to mid 80's all week.
Hoping to see low 40's up front. Time will tell.
Not expecting anything super cold from the rear unit as the evaperator is, I think, in the quarter panel. It's just ducted up and overhead. My old '72 Burb, however, had the evap right behind the third row seat, overhead, about neck level.......TXV system both ends, I think, and of course R-12. That was pretty cold! On a hot day everybody fought over the back seat......
Getting some time free first of next week to get back on it. I'll let you know how it goes.......Thanks, everyone!

70monte on Sat August 20, 2011 2:17 AM User is offline

I have a factory Helm Service manual for 98 chevy trucks which include the tahoe and Suburban and the refrigerant capacity stated in the manual for tahoes and Suburbans with rear air is 4lbs. For these vehicles without rear air, it says the capacity is 2.25lbs.

We had a discussion about the capacity for Subs and tahoes on the other AC forum and it seems that there is all kinds of different information out there on the correct charge and no one seems to agree on what is correct.

Maybe they installed the wrong label on your tahoe. I guess the best course of action is to start with the 44oz and see how your cooling and pressures are.


Stresst on Sat August 20, 2011 5:31 PM User is offline

I charged mine with 4lbs but my pressures are now kinda high. IMHO its more like 3.5lbs or 56ozs. Like already stated there is a ton of bad information floating around with these trucks. I have charts also which state everything from 44 to 64ozs.......

2000 Cadillac Escalade w/rear air

Hardrock on Mon August 22, 2011 1:15 AM User is offline

Just for comparison, I went out and checked the factory label on my '96 Tahoe. 2 lbs. 4 oz.
It's a 2 door 2WD, though. No rear air. Should be same as a '96 pickup in that respect.

My '90, '91, and '93 work pickups all have R4/R-12 systems and show 2 lbs. even.
Everything in the R-12 trucks show a different part # than later R-134a trucks.
I knew the compressor, lines, and condenser were different, but the evap appears to be different also.

Hardrock on Sun August 28, 2011 1:42 PM User is offline

Well, finally got the truck to the AC shop Thursday.........
After a 2 hr. vac, it got a pressure check and the 44 oz. charge of R-134a per the OEM sticker.
The tech added the final 2 oz. of dyed PAG and everything went pretty smooth. No leaks.

Here's what I came away with...............

The high side @ 185, low side @ 34 with 82* ambient.

Idling in the shop with a floor fan up front, doors open, full speed blower, he got 54* center vent temps.

2000 RPM same setup, he got 46*.

On the road, same afternoon, we both got 40* center vent temps.

Suprisingly, to me anyway, the rear vent temps going down the road were 42*.

I'm pretty happy with the results. Do these numbers sound about right?

I know with R-134a and an OT system, low speed cooling is pretty lame, but should there be such a temp swing as the figures show?

Thanks for your help, everyone! Mike

70monte on Fri September 02, 2011 7:39 PM User is offline

It looks like your pressures and final vent temps look good and at the lower refrigerant amount. I would be happy with those results.


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