PAG 46 Oil Charge-96 K2500 Suburban 6.5 with Rear Air

[turbopower6]

Hi Folks,
Just about to replace the AC compressor and condenser with new components after a leak check shows some issues that translated into lower cooling efficiency. Thankfully there does not appear to be a catastrophic compressor failure. I will be flushing the lines and inspecting for debris to be on the safe side.
I understand the 96 Suburban with rear air takes 11 oz of PAG150. I also understand that GM recommends replacing the old refrigerant oil with the lower viscosity PAG46 when doing repairs. I will drain the oil out of the new Delphi compressor before installation and measure the amount that comes out. I assume I cannot get "all" of the oil out. The question is ...at that point do I add 60% of the 11 oz back into the compressor (@6.6 oz) and add the additional 4.4 oz while recharging?
I plan on replacing the receiver dryer as well but have been warned that the connection to the evaporator is a mother to get off! While I have it off I plan on flushing it out as well. Any hints on this process. i.e. 40 PSI of cleaner through the bottom and out of the top....then 30 minutes of shop air to dry her out and exhaust any solvent, oil "shit' before reinstalling the lines. Does anyone recommend adding an additional inline filter in the event I miss some of the debris to avoid blowing up the new compressor in the future. Where would be the optimal place to add this in line filter?

 

[WarWagon]

Do replace the accumulator as it takes the water out of the system. It's "dead" after being exposed to the air for 2 min. Pull a vacuum on the system for a minimum 30 min. You have something better to do than take a shortcut on vacuum time and leave water in the system? Do it right the first time rather than take additional time to do it over.

Flushing the system is difficult with the rear TXV left in place. It's a real bitch to get to it. To remove the oil oil you must remove the TXV to flush the rear evaporator. If it's the older style threaded fittings you best leave it alone rather than strip the seized threads.

Inline filter without a compressor failure is adding more to leak and go wrong. There is nothing to filter out at this time.

IMO, KISS. You need to fix the leaks and add PAG 150 oil for replaced components. NO FLUSHING NEEDED! The above is just making the job more complicated for no good reason. Don't bother switching oils to the new recommended oil as it is causing you more grief for no reason. If you were replacing the compressor and then doing the required from compressor failure flushing the entire system then start with new oil. Even then I hate thinner oil for any reason esp. in my extreme heat. GM's oil recommendations are not the Bible as some are 100% wrong and cost many warranty repairs aka factory synthetic in a differential when the posi unit calls for dyno oil only and quickly fails with synthetic oil... If you have your heart set on changing the oil to PAG 46, remove and drain as much as you can from the compressor: the above PIA TXV valve will need to be removed to flush the system. (A lot of oil from being low on charge will be left in the rear evaporator.)

Replacing the accumulator: you need to measure the amount of oil you can get out of it and then consult a table to add slightly more oil. When a system is low the oil gets distilled and left in the evaporators and may spill over into the accumulator and stay there depending on how low the charge was. This is why you must measure the oil in the accumulator.

 

[turbopower6]

Do replace the accumulator as it takes the water out of the system. It's "dead" after being exposed to the air for 2 min. Pull a vacuum on the system for a minimum 30 min. You have something better to do than take a shortcut on vacuum time and leave water in the system? Do it right the first time rather than take additional time to do it over.

Flushing the system is difficult with the rear TXV left in place. It's a real bitch to get to it. To remove the oil oil you must remove the TXV to flush the rear evaporator. If it's the older style threaded fittings you best leave it alone rather than strip the seized threads.

Inline filter without a compressor failure is adding more to leak and go wrong. There is nothing to filter out at this time.

IMO, KISS. You need to fix the leaks and add PAG 150 oil for replaced components. NO FLUSHING NEEDED! The above is just making the job more complicated for no good reason. Don't bother switching oils to the new recommended oil as it is causing you more grief for no reason. If you were replacing the compressor and then doing the required from compressor failure flushing the entire system then start with new oil. Even then I hate thinner oil for any reason esp. in my extreme heat. GM's oil recommendations are not the Bible as some are 100% wrong and cost many warranty repairs aka factory synthetic in a differential when the posi unit calls for dyno oil only and quickly fails with synthetic oil... If you have your heart set on changing the oil to PAG 46, remove and drain as much as you can from the compressor: the above PIA TXV valve will need to be removed to flush the system. (A lot of oil from being low on charge will be left in the rear evaporator.)

Replacing the accumulator: you need to measure the amount of oil you can get out of it and then consult a table to add slightly more oil. When a system is low the oil gets distilled and left in the evaporators and may spill over into the accumulator and stay there depending on how low the charge was. This is why you must measure the oil in the accumulator.

Thank you for the input War Wagon. I will be guided more once I disassemble the condenser and pull the orifice tube to see what goodies I will find. At this point I do not have a catastrophic compressor failure as far as I know and may well have averted bigger problems. I figured while I was opened up, and replacing components, I would flush as I go along in the event some small debris was deposited in the lines under the hood and in the evaporator etc. I will be draining the oil and measuring it from the new compressor and doing the same for the old to determine how much new oil to add before installing the compressor. Likewise for the condenser I will add 1 oz PAG and for the accumulator 2oz PAG per the Delphi install recommendations.

I thought I read somewhere along the line that flushing an evaporator in the vehicle is not a great idea snce it may be difficult to get all the smudge out even if you run dry air or nitrogen through it for like an hour or so!

I am thinking if I see little evidence of "debris" on the removal of the orifice tube that will give me a better sense of what may lie ahead in the rest of the system and components and detrimine the need to flush more aggressively than in the lines. I like the KISS method but understand I am hoping to do this project just once...Thoughts?

 

[THEFERMANATOR]

Your orifice tube ISN'T at the condenser in a dual air unit, it is behind the Y pipe on the passenger side fenderwell. Be forewarned if you TOUCH the lines at the condenser, I give you a 98% chance the threads will strip off of the condenser. The bad part is there are no manifold assembly's anymore, so the hose assembly going from the compressor out to the condenser will be on you to find somebody to fix the connections on it. As to compressors, I do hope you bought a GPD as any of the factory replacements will all suffer the same failure in a short amount of time. The R 6 design is just a poor design. The SANDEN compressor used to be a good option, but a local shop I use said he had a 100% failure rate on the SANDEN R6 replacement compressors he sold(mine was one of them). I personnally like the PAG 46 oil from my own experience, but I don't think it is imperitive to get every drop of the PAG 150 out. The basic rule is 1 ounce for the condenser, 2 ounces for the accumulator, 2 ounces for the evap, 2 for the compressor, and 1 for residual in the lines. If it has rear air you add 2-3 ounces for that. I always do the accumulator, repalce the low pressure switch with an AC DELCO, add in a relay on it to handle the actual compressor powering duties if you want to never replace your low pressure switch again, replace the orifice, and put a new GPD compressor in it. You can do the rear expansion valve by cutting the evap housing if you get the GM template, and is the ONLY way I would even consider doing one of this age unless somebody had already done the lines(and guess what, those rear lines are also discontinued now, so you're getting custom built if theres a problem there too).

 

[turbopower6]

Your orifice tube ISN'T at the condenser in a dual air unit, it is behind the Y pipe on the passenger side fenderwell. Be forewarned if you TOUCH the lines at the condenser, I give you a 98% chance the threads will strip off of the condenser. The bad part is there are no manifold assembly's anymore, so the hose assembly going from the compressor out to the condenser will be on you to find somebody to fix the connections on it. As to compressors, I do hope you bought a GPD as any of the factory replacements will all suffer the same failure in a short amount of time. The R 6 design is just a poor design. The SANDEN compressor used to be a good option, but a local shop I use said he had a 100% failure rate on the SANDEN R6 replacement compressors he sold(mine was one of them). I personnally like the PAG 46 oil from my own experience, but I don't think it is imperitive to get every drop of the PAG 150 out. The basic rule is 1 ounce for the condenser, 2 ounces for the accumulator, 2 ounces for the evap, 2 for the compressor, and 1 for residual in the lines. If it has rear air you add 2-3 ounces for that. I always do the accumulator, repalce the low pressure switch with an AC DELCO, add in a relay on it to handle the actual compressor powering duties if you want to never replace your low pressure switch again, replace the orifice, and put a new GPD compressor in it. You can do the rear expansion valve by cutting the evap housing if you get the GM template, and is the ONLY way I would even consider doing one of this age unless somebody had already done the lines(and guess what, those rear lines are also discontinued now, so you're getting custom built if theres a problem there too).

Hi Ferm,
Of course the adventures never end with these vehicles. Should we bill GM for all of the "engineering" and "modifications" we all have done to keep their trucks going beyond a factory warranty period? Yikes!

I digress...!

I thought the orifice tube was in the condenser because I asked the supplier where I purchased the condenser about it. We took it out of the box and removed one of the plastic shipping caps and inside the tube was the plastic end of the orifice tube...answer..."yes it comes with the orifice tube."

Having not disassembled this system before I was not sure where it was located. Always something....!

I am replacing the condenser as it has small leaks on the sides showing, after we added dye to leak check, and expect to be VERY careful when removing the fittings. 98% chance is not a happy thought...and today I am not happy after hearing the "good" news of one more adventure about to begin.

I understand the accumulator is a mother also. Is there anything on these vehicles that goes easier than...1) spending more money and 2) adding more fuel?
I squirted a little JB 80 on the AC fittings to ease them up in the event they are a bit corroded. I will be sure to clean everything carefully upon disassembly and reassembly to avoid contaminating anything inside the ac system.

I did get a Delphi unit...upon recommendation from the AC shop who acknowledged these systems are often problematic as you stated. They indicated that as long as I follow the install instructions I should be OK. They emphasized the importance of balancing the oil in the system as a critical piece of the process. I will carefully measure what is coming out of the old components and adding as required to make up the correct amount. The last question I have is about the PAG. Delphi is recommending a top off of Synthetic RL-488 or Equivelent. I understand this is a Union Carbide factory fill oil with a viscosity around 132. Now the quandary....do I use PAG 150? PAG 100? or PAG 46 Single end capped. Or just roll with the lighter PAG 46 That GM is using in all of their R134A Systems?

Why does everything have to be so complicated when there is so much at stake considering all of the subsequent ac failures after component replacement.

 

[THEFERMANATOR]

For single A/C systems the orifice goes in the condenser, for dual air systems it goes just after the Y. If you leave the orifice in the condenser, you will lose your compressor in short order if the system will even work. The orifice tube is for JUST THE FRONT system, the Y that splits the flow is AFTER the condenser, so the orifice has to be AFTER the Y. Otherwise you end up with 2 orifice tubes, and no return flow to your compressor which means no flow, no oil flow, and compressor death if you let it try and run for too long like that. Condensers USED to come with a notice on them to remove the orifice if it was going into a dual A/C system.

You can try some heat and them spray aerokroil on the fittings and let it sit to try and loosen up the corrosion that will be present. The problem is GM used aluminum on the end of the tube, but a steel nut, PAG is a corrosion agent, so the dissimiliar metals seize themselves together. I have yet to see a condenser leak as they are a pretty tough design, but anything is possible. I always avoid touching them at all costs if at all possible because of all the problems with no more parts available, and they almost always strip the threads off.

As to the DELPHI compressor, they fail just as often as any of the others. It's the design of the compressor that is the issue, and GM/DELPHI have never made any changes to the infamous belly leaker design of the R6. The aftermarket has fixxed this issue, hence why many shops REFUSE to install an OEM compressor in an R6 application, or if they do, they state NO WARRANTY on the system, only on workmanship. If it's a DELPHI compressor, I would go down and get a bottle of GM compressor oil from the dealer. it will most likely come in a spot gun tube, and will be a PAG 46 most likely.

 

[WarWagon]

I am confused as to if you are or are not changing the compressor out. This may be a good time to do so for an improved aftermarket design. IMO use the oil that's in the system as you are not flushing it all out and would have a mixed oil situation if you don't. Do you really want to experiment with mixing oil viscosity? A little left in the compressor is a non-issue, but, most of the system being on something else: why?

As an aside you do not have the AC failures like we do in Phoenix, AZ using the system hard at extreme temps and pressures year around... Regardless the corrosion and locked up fittings may be worse with higher humidity as PAG + moisture = acid.

 

[turbopower6]

I am confused as to if you are or are not changing the compressor out. This may be a good time to do so for an improved aftermarket design. IMO use the oil that's in the system as you are not flushing it all out and would have a mixed oil situation if you don't. Do you really want to experiment with mixing oil viscosity? A little left in the compressor is a non-issue, but, most of the system being on something else: why?

As an aside you do not have the AC failures like we do in Phoenix, AZ using the system hard at extreme temps and pressures year around... Regardless the corrosion and locked up fittings may be worse with higher humidity as PAG + moisture = acid.

So I m changing the compressor in this repair along with the condenser and Receiver Dryer. You would think the aftermarket at Delphi would use PAG 46 since GM has evolved to this. I agree about not wanting to "mix" oil in the system. After all....why compound the problems GM "Engineered" into these adventures! Like the dissimilar metal issue. These geniuses went to engineering school and came up with that set up ll by themselves. I guessif they started on the shop floor like the old days they would not make that mistake.
I will remove the orifice tube in the condenser and place it in the correct location as mentioned past the Y. I believe you are correct bout the PAG 46 needing the "caulk gun" approach. I have a buddy with a shop that has one and can lend it to me. I am trying to find a low humidity day to crack open the system and replace these components to minimize the time it is open to the atmosphere. I plan on doing a real long evacuation after I leak check with the vacume pump. Like on the order of 2-3 hours to make sure I evacuate as much moisture as I can. Since this is for me and not a shop that needs to make money on the repair...time is less an issue for me. Any other tips?