88-94 5.7 Suburban A/C Diagnosis and Tuning

[L31MaxExpress]

Got to dedicate a day to the Burb yesterday. My plan was to:

1) Replace the tube-fin condenser back to a parallel flow,
2) Replace the accumulator with the correct, larger one for dual air trucks,
3) Replace the R12 TXV in the rear with a R134 specific one,
4) Add a reciever-drier to the rear system to feed the TXV better quality refrigerant.

I pulled all the old components, and recovered as much oil as I could pour out from them (about 3oz). Oil looked good, no off colors or metal flake.


Assembly

Parallel flow went in no problem, made sure there was no o-tube pre-installed. Put 2oz in there. Accumulator went in fine, other 2oz in there of fresh oil.

Old TXV had a tiny filter screen with a little gunk in it; was hopeful this was contributing to my issues.

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I replaced the TXV with the R134 specific version, which had no internal screen. Rear rebuilt:

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Side note, earlier in the thread I was looking for a body seal for the rear A/C lines; I bought the 95+ one that was posted and it's not even close. Needed to make my own seal:

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Reinstalled the rear A/C box into the truck, then mounted up my mini reciever-drier. Used the same bolts that hold the air box down to mount it, so no drilling required. Was able to adapt the factory lines to work, so it is totally reversible if it doesn't work.

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It also has a sight glass on top so with an inspection mirror I can see inside the system.

Charging

Vacuumed it down for 30 mins, held it there for an hour, got to -13.9 psi. Charged it with two 10oz 152a cans to start, then slowly started adding refrigerant on the 3rd can, feeling the line temperature right after the o-tube and comparing it to the suction line off the accumulator.

Long story short, 3 full cans in and the accumulator suction line never got cold. Added a bit more but it wasn't getting any better, so i stopped around 35oz. And here's the results:

Ambient temp 105°, idle, 15% humidity...

Low side: 65psi
High side: 215psi.

Rear sight glass has some bubbles but isn't foaming, it looks ok.

Now what? The performance is way worse now, somehow.

My suggestion is keep adding refrigerant. At 215 psi in that kind of heat with a warm accumulator, you are still a good bit low. The suction side pressure will drop when the charge level gets closer to where it needs to be.

 

[L31MaxExpress]

I filmed this a few minutes ago and it just finished uploading.

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[L31MaxExpress]

This was my Black on Black Infiniti M56S, it started out around 145°F inside, even with dark tint on it. R152a has great initial cooling.

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[Schurkey]

Assembly

Parallel flow went in no problem, made sure there was no o-tube pre-installed. Put 2oz in there. Accumulator went in fine, other 2oz in there of fresh oil.

You drained 3 oz, installed 4. But now there's an added receiver dryer, and a bigger accumulator. And there's no knowing how much oil wasn't recovered. I think you're a little shy on oil.

Old TXV had a tiny filter screen with a little gunk in it; was hopeful this was contributing to my issues.

Well, that's completely disgusting. One wonders where those metal shavings came from *cough* Compressor *cough*.

Charging

Vacuumed it down for 30 mins, held it there for an hour, got to -13.9 psi.

-13.9 psi? As in, about 16 inches of mercury vacuum? NOT NEARLY ENOUGH. You should have something like 30 inches of mercury vacuum, or "0" pressure.

Your system has air in it. MAYBE has water (humidity) in the system, too. Vacuuming the system does two things: Removes air, and lowers the boiling point of water. You need to hold the vacuum long enough for all the water to boil and be removed. At around 30 inches of vacuum, water boils at approx. 70 degrees.

 

[L31MaxExpress]

You drained 3 oz, installed 4. But now there's an added receiver dryer, and a bigger accumulator. And there's no knowing how much oil wasn't recovered. I think you're a little shy on oil.


Well, that's completely disgusting. One wonders where those metal shavings came from *cough* Compressor *cough*.


-13.9 psi? As in, about 16 inches of mercury vacuum? NOT NEARLY ENOUGH. You should have something like 30 inches of mercury vacuum, or "0" pressure.

Your system has air in it. MAYBE has water (humidity) in the system, too. Vacuuming the system does two things: Removes air, and lowers the boiling point of water. You need to hold the vacuum long enough for all the water to boil and be removed. At around 30 inches of vacuum, water boils at approx. 70 degrees.

-13.9 psig would be like ~28 in/hg vacuum. PSI(G) assumes atmospheric pressure is the Zero starting point. Vacuum thus negative pressure. 1 psi is roughly 2 in/hg. Hopefully he clarifies that since most of us measure ac vacuum in in/hg. Needle should get close to 30 in/hg atleast in my elevation.

Edit-Meant to say PSIG not PSIA.

 

[Wildblue19]

Thanks for the replies. Added 10oz more 152 and it's doing a bit better. Delta of 45-50 after 10 minutes on the highway with recirc on. I want to drive it a while to let things circulate and see what it needs and get data.

Light or heavy on oil, who knows. The gunk in the TXV is probably from 3 compressors ago, the original R4. Never removed the TXV to check it out. Flush had no chance to clear that out.

Yes, it's gauge pressure, zeroed at local atmospheric. Max theoretical at my elevation is -14.1 so it's plenty evacuated.

 

[Schurkey]

My mistake. Error in converting units.

 

[Wildblue19]

Really warm day today, got to drive the truck after a long heat soak in the parking lot. Conditions were 106° ambient, 15% RH, internal air in the cabin was 130°.

Front vents: at idle, it cooled down to around 75, delta of 30 with recirc on. Driving in town, avg 30mph, hit a delta of 35-38. On the highway, delta was 45, vents blowing 58-60° and slowly cooling more. On a longer drive it would probably see 50+ delta.

Thankfully, the rear system is operating better than the front, averaging 3-5° cooler. The reciever drier addition is helping. Combined, the systems are enough to take the edge off. I'd like to drive low side pressures lower, but I don't think I can with the limits of the current setup.

I believe the reason the low side pressures are higher is that the rear 134 txv has a larger orifice than the r12 version. But the increased volume of refrigerant is able to make up for the increased pressure on the low side.

I found a COP chart for my compressor, ill try to find and post here. Does anyone know if there is a comparable performance chart for the R4 compressor?

 

[L31MaxExpress]

Really warm day today, got to drive the truck after a long heat soak in the parking lot. Conditions were 106° ambient, 15% RH, internal air in the cabin was 130°.

Front vents: at idle, it cooled down to around 75, delta of 30 with recirc on. Driving in town, avg 30mph, hit a delta of 35-38. On the highway, delta was 45, vents blowing 58-60° and slowly cooling more. On a longer drive it would probably see 50+ delta.

Thankfully, the rear system is operating better than the front, averaging 3-5° cooler. The reciever drier addition is helping. Combined, the systems are enough to take the edge off. I'd like to drive low side pressures lower, but I don't think I can with the limits of the current setup.

I believe the reason the low side pressures are higher is that the rear 134 txv has a larger orifice than the r12 version. But the increased volume of refrigerant is able to make up for the increased pressure on the low side.

I found a COP chart for my compressor, ill try to fi d and post here. Does anyone know if there is a comparable performance chart for the R4 compressor?

As I have stated before, until you get cool refrigerant into the accumulator and suction lines, the low side pressure will be elevated. The low side pressure will drop as the refrigerant starts to cool the suction lines.

This was after I parked to unhitch the trailer today in 108F. Interior had cooled down very well at that point.

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[Wildblue19]

Copy, I should have said the suction lines are cold now after adding the extra refrigerant. I haven't checked subcool or superheat yet but it was charged until the feel between the lines after the orifice and off the accumulator felt the same.