1999 GMC Yukon

[Mark86]

Hey guys, back working on another project.

1999 GMC Yukon SLE 5.7L with rear AC. Was my late fathers and I brought it down to Phoenix from South Dakota and getting the AC working is on the top of the list. Vehicle sat in the garage for many years and is in great shape.

Issue #1. No charge at all in the system. Had to go somewhere so I pressurized the system with nitrogen up to 200 psi and went on the hunt. Could not hear anything but then a slight air noise by compressor. foamed it with soapy water spray and it bubbled and foamed from every joint on the HT6. From what I understand the HT6 is prone to leaking. I would like the best replacement compressor, what do you recommend?

Second is I split the line (Y PIPE) and...... no orifice tube. So I pulled the grill and split the outflow line from the condenser and there was the orifice tube. Maybe I'm not seeing the big picture here but on a dual (front / rear) system shouldn't the rear expansion valve receive high pressure liquid Freon? So what was the orifice tube doing in the condenser pipe AHEAD of the Y-pipe. Was somebody trying to fix something?

The AC worked just fine as I recall, but that was 10-12 years ago. I don't recall ever running the rear AC unit though. The orifice tube I pulled out is white and yellow, which the vehicle calls for. It was clean. I cleaned it in alcohol and installed a new O-ring and installed it aft of the Y block in the location I believe to be correct, (crimp marks) which would service the front evaporator. Now this will allow high pressure Freon to flow to the rear unit.

I didn't replace the condenser, as it's in great shape, maybe it was replaced at one point, hence why the orifice tube was there, but doesn't explain why the one in the Y-pipe was missing. The condenser is a parallel flow, about 30 rows and an inch thick. Which would be correct for dual AC.

Also, can swing by in person and pick up parts here in Phoenix?

[JohnHere]

Issue #1. No charge at all in the system. Had to go somewhere so I pressurized the system with nitrogen up to 200 psi and went on the hunt. Could not hear anything but then a slight air noise by compressor. foamed it with soapy water spray and it bubbled and foamed from every joint on the HT6. From what I understand the HT6 is prone to leaking. I would like the best replacement compressor, what do you recommend?

The GM HT6 has a reputation as one of the most troublesome compressors ever. It was known as a "belly leaker" because the o-rings at the case joints leaked frequently. I wouldn't bother trying to re-seal your existing compressor. I would simply replace it with a brand-new updated unit. Contact Tim at ACKits.com, this Forum's sponsor, for details.

Second is I split the line (Y PIPE) and...... no orifice tube. So I pulled the grill and split the outflow line from the condenser and there was the orifice tube. Maybe I'm not seeing the big picture here but on a dual (front / rear) system shouldn't the rear expansion valve receive high pressure liquid Freon? So what was the orifice tube doing in the condenser pipe AHEAD of the Y-pipe. Was somebody trying to fix something?

You're right that the rear TXV should receive high-pressure liquid refrigerant and should not be throttled by an OT. Apparently, someone put the OT in the wrong place.

The AC worked just fine as I recall, but that was 10-12 years ago. I don't recall ever running the rear AC unit though. The orifice tube I pulled out is white and yellow, which the vehicle calls for. It was clean. I cleaned it in alcohol and installed a new O-ring and installed it aft of the Y block in the location I believe to be correct, (crimp marks) which would service the front evaporator. Now this will allow high pressure Freon to flow to the rear unit.

Sounds to me like you now have the OT in the right location. But why not replace it with a new one? They're only a few dollars. However, you are correct in that the OE OT is yellow and white, and it also has a .062" orifice.

I didn't replace the condenser, as it's in great shape, maybe it was replaced at one point, hence why the orifice tube was there, but doesn't explain why the one in the Y-pipe was missing. The condenser is a parallel flow, about 30 rows and an inch thick. Which would be correct for dual AC.

Since the compressor didn't disintegrate internally, the existing condenser, which acts as a filter in the case of catastrophic compressor failure, should be fine. Apparently, the technician "forgot" where the OT should go.

Also, can swing by in person and pick up parts here in Phoenix?

ACKits.com is headquartered in the Phoenix area.

[Mark86]

Thanks John. I'm on the hunt for a Sanden (single case) compressor. Checked with Tim and he would have to order it in or drop ship it. Would like to compare the units in person. I reused the OT because I didn't have another one in hand and it looked new and came out undamaged. This was installed prior to the leak check which then presented the leaking compressor.

[Mark86]

Found a Sanden 4440 in captivity here in PHX. That HT6 design is beyond reasoning why they would introduce so many points of seal failure. Now, on to a vacuum / leak test.

[JohnHere]

In my humble opinion, the single-case design of the 4440 (SD7H15) is superior to the multi-case design of the HT6. Check carefully, but I believe the Sanden should bolt right up.

Sounds good about the OT.

The OEM specifications that I have for your vehicle are as follows: 64 ounces net weight of R-134a, and 11 fluid ounces of PAG-150. If the under-hood decal specs differ, the decal always takes precedence.

[Mark86]

Thanks John.

The round sticker was present on the accumulator, which I believe to be original. It states two service charge amounts, one for the "4 door utility" and one for the "suburban" I'm assuming the Yukon and Tahoe are the "4 door utility". It states 2 lbs, 12 oz for the 4 door utility, which is 44 oz. The Suburban charge is 3 lbs 8 oz or 56 oz. It gives no oil amount only to service with (GM part #) synthetic oil and to refer to manual for amount.

There was no rapid loss of refrigerant and I'm assuming it all gassed off out of the compressor seals slowly over time, which was not oily or signs of oil residue on compressor case. About a tablespoon of oil came out of the old compressor ports.

I did no flushing so whatever oil is in the system should still be there.

I put 2 oz in the new accumulator, and 2 ounces in the intake port on the compressor. Installed and rotated the compressor to move the oil around. Used PAG 150.

[JohnHere]

Interesting that in the *GPD Refrigerant & Oil Guide* that Tim posted in the Automotive Air Conditioning Procedures, Tips and FAQ sub-forum shows the same specs that I posted yesterday, which was 64 ounces net weight (4 pounds) of R-134a, and 11 fluid ounces of PAG-150. Regardless, I would still go with what the decal says for the refrigerant: 56 ounces net weight (3.5 pounds) of R-134a.

As for the PAG-150 oil, I'm guessing that the new Sanden would take about as much oil as the old HT6. So if you figure that your vehicle has rear A/C, and you didn't flush the system, I'm also compelled to guess that you probably still have about 1.5 ounces of oil in each of the two evaporators, about 2 ounces in the lines/hoses running from front to back, about 0.5 ounce in the lines and hoses under the hood, and about 1.5 ounces in the condenser. Together with the 2 ounces that you added to the new accumulator and 2 ounces added to the new compressor gives a total of about 11.0 fluid ounces of oil now in the system—just what the printed specifications read. So I think you're good on the oil.

[Mark86]

Thanks for the additional specs. After 26 years and a misplaced orifice tube, who knows if that accumulator is original. I'm guessing it is because the decal is a GM decal. I'll charge to that spec and report back on temps and pressures. I wonder if there was a TSB or other guidance from GM to increase the Freon amounts?

https://www.4s.com/media/3656/four-seas ... -guide.pdf
I referenced at various times a pdf doc that I believe Four Seasons compiled and it's about 50/50 on accuracy. It was off on my 2000 1500 Silverado. That document indicates 64oz for this application as well.

[Mark86]

Image of the charge specs for 1999 YUKON TAHOE SUBURBAN

https://i.postimg.cc/SxPDkqyP/IMG-2653.jpg

[JohnHere]

Thanks for the additional specs. After 26 years and a misplaced orifice tube, who knows if that accumulator is original. I'm guessing it is because the decal is a GM decal. I'll charge to that spec and report back on temps and pressures. I wonder if there was a TSB or other guidance from GM to increase the Freon amounts?

I agree that the decal in the photo looks like it's genuine GM, and it is somewhat cryptic. But I wonder why GM would apply it to the accumulator, a part that would normally be replaced every time the system is opened for whatever reason (and the decal lost after the first replacement). Typically, the decal is affixed to either the radiator support or to the underside of the hood.

If GM Tech sees this post, maybe he knows the reason why and whether there was a TSB issued.

Once you get the system back together, evacuated, and recharged, please *do* post the pressures, center vent temperature, and ambient temperature. As you probably know, performance testing should be done at ~1,800 RPM with the compressor engaged, system set to Max Cool, blower on medium or high, the condenser fan(s) roaring, and the doors/windows open to maximize the heat load. In the Phoenix area, the latter shouldn't be too hard to achieve