'99 OBS Suburban with rear A/C, R134A capacity?

[me51]

Vehicle in question is a 1999 Suburban LT 5.7 (last of the square old body style) with front & rear AC.

So some time ago the A/C compressor was replaced (due to the typical "belly leak") with a Delphi CS0120 along with a new drier/accumulator, and it was charged to the R134A amount that all service literature says: 4 LBS (1.81 KG). The system was still cooling very well with the old compressor.

The workshop that did the work was not able to replace the orifice tube ("we couldn't get the old one out" ) and the rear expansion valve. Not ideal but I figured since the old compressor still worked perfectly fine and didn't explode, it should be ok.

With the new compressor cooling output has been greatly reduced, at best it'll do around 50°F (10°C) at the outlets when it's close to 90°F (30°C) outside. Air temperature coming out front and back feels about the same. Before it felt like a fridge, now it's kinda so-so. I noticed that the old drier has a sticker on it saying that it should be charged with 3 LBS 8 OZ (1.588 KG), which is interesting because that contradicts with the GM manual and all info on the internet.

The fan clutch is new and engages in hot weather when sitting in traffic, so that operates as it should.

Any opinions on why it has such weak AC performance?

 

[exp500]

Oriface tube partially plugged or undercharged.
Sometimes, on these old ones they wind up overfilled with oil due to poor servicing or carelessness when flushing.This usually creates a slugging where oil fills the low spots in the line rather than a film. With the reduced capacity in the system the charge acts funny, borderline hi pressures. I hope my description is understandable to you. Still drinking 1st cup of coffee. Good Luck and keep posting results.

 

[me51]

The shop did not flush the system since there was no reason to do that, they only swapped out the compressor. I hope they put the correct amount of oil in it, the compressor shipped with oil pre-filled.

Do you know what the deal is with the two different capacities for the same version?

Shop just says it cools, what else do you want

 

[exp500]

Some other tests are - rear air is excellent, front weak definate Orifice Tube. (1st guess for you is undercharged)
Shooting the temps with IR temp gun helps narrow down problems. Start at compressor discharge and work your way downstream. Both sides of Orifice Tube, receiver/dryer, right on down the line with compressor running.Also shoot air temps f/r . Useful when icing a problem too.

 

[me51]

Rear air feels identical to the front air. I'll check the temperatures of the compressor input and output once it's warmer outside again.

 

[OR VietVet]

That shop is lacking in common sense. The compressor gets changed and the accumulator should be changed too. They make orifice tube repair kits but I hate them. They always leak. Change that evaporator if needed. The system should be flushed, especially if enough crud is in the system that keeps the orifice from being removed. Did that shop say the accumulator should be changed and you said no or did they even mention it?

 

[me51]

I brought a new compressor, drier/accumulator, o-rings, orifice tube and expansion valve. The new compressor, the o-rings and drier/accumulator were put in. System was evacuated, held a vacuum and was recharged.

They just told me that they couldn't get the orifice tube out and left the old one in it.

 

[OR VietVet]

The system takes 4 lbs. R134A or 64 ounces. Does not sound like the system was flushed and those condensers had clogging problems, if I remember right. I could be wrong about the condensers. That orifice needs to be changed or swap out the part it is mounted in. They used to be at the evaporator but I have not dealt with the ones at the condenser.

 

[me51]

The system takes 4 lbs. R134A or 64 ounces...

That is the interesting part from the first post. The old drier/accumulator had a sticker on it saying 3 LBS 8 OZ -> 56 OZ, and I can guarantee that no one except the factory has touched that system before.

Why was the spec changed? I think the "newer" spec is wrong, and it's just overcharged now. I have to see if I can get someone to connect gauges to it and see if they indicate an overcharge.

 

[OR VietVet]

That is the interesting part from the first post. The old drier/accumulator had a sticker on it saying 3 LBS 8 OZ -> 56 OZ, and I can guarantee that no one except the factory has touched that system before.

Why was the spec changed? I think the "newer" spec is wrong, and it's just overcharged now. I have to see if I can get someone to connect gauges to it and see if they indicate an overcharge.

Confucius say, "Dig deep grasshopper and find the answers your heart wishes for".

 

[me51]

So reducing the charge to 3 LBS 8 OZ makes the system barely cool at all anymore. So it is currently filled at 4 LBS and cools okay-ish, guess it's better than nothing

Still makes me wonder why the slow-leaking OE compressor worked so much better than the new one, my guess is that the system is overfilled with oil since they didn't mention doing anything with the oil volume. I was told "we always just put them in the way they come", but the box had instructions for oil balancing which they ignored. My research tells me that excess oil is impossible to get out unless you replace all AC components since it sticks to the walls of all the components.

This reminds me why I always hate going to workshops, they almost never ever do the work right.
Should have gotten an AC certificate and do it mightself in hindsight

 

[OR VietVet]

So, no flush, bad decision. The 3.5 pounds sticker does not take in to consideration that has rear a/c. The a/c part you install does not know that. Excess oil can get out with a flush.

 

[me51]

They told me when they took the lines off the old compressor that they were clean (no grey goop) so the system was not contaminated. I'm sure they did not do a flush then, the bill only said evac & charge.

Googling tells me that there are two different kinds of AC flush techniques available:
- Fill and evacuate with liquid R134A a couple of times (works with commonly used AC machines)
- Evacuate the system, then use a flushing liquid together with compressed air, then dry the system with nitrogen (needs special hardware)

3.5 LBS was the original sticker on the vehicle, the picture I took of it says:
Use only R134A or equiv
Suburban 3 lbs 8 oz (1.588 kg)
Yukon/Tahoe 2 lbs 12 oz (1.247 kg)
and Synthetic Oil #12345923 ...

 

[OR VietVet]

The second one is how I used to do it.