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  Misc. Information


The root cause of the repeat-failures of the DENSO compressors on Tahoe/Yukon/Suburban is oil starvation, but it’s a problem unrelated to the Suburban. In certain operating conditions, the oil accumulates in the rear evaporator (typically front A/C off, rear on with lower blower).

It’s a known problem, particularly on 2000-2001 models, and the fix also is known: covered in a bulletin (No. 01- 01-39-002B, issued 12/03/01) but the part numbers are outdated. However, it explains how to change all the plumbing to improve oil circulation (basically a rear line bypasses the accumulator, going directly to the compressor).

We’re not going to repeat the procedure here, as you should have access to service bulletins, but there are some important things you should understand about this fix specifically, and General Motors service procedures for compressor failures.

For this fix, a lot of new parts are required – just flushing and replacing the condenser, accumulator, orifice tube won’t produce a lasting repair. Now let’s talk flushing:

As we’ve noted earlier, unlike Ford, GM never validated a solvent flush. Why? It’s a difference in service procedure philosophy among the A/C service engineering teams and the service equipment suppliers with whom they work, plus the debris from failures it was seeing.

GM decided it wanted to flush only to remove dirty oil, such as from desiccant failure and a small amount of metal. It could do that with liquid R-134a, adapters and a special port on its new recycling machine, which dealers already had, rather than add a new machine and flushing agent. GM had used liquid-line filters for some time, was satisfied with them, and trusted suction screens as finishing touches And as part of factory fixes, it changes accumulators and even condensers where indicated.

An important note: even if you flush with liquid refrigerant and aren’t trying to get out a lot of debris, you still have to remove the orifice tube and expansion valve (rear system in this case), the accumulator and any lines with mufflers. GM has an adapter kit (No. 45268) to bridge the joints, although shops also have made their own, such as by taking failed expansion valves and drilling through them. But the shop-made adapters won’t have the filter the GM kit includes.

The GM approach is to back-flush front and rear systems separately, front first, blocking one while flushing the other. And with the needed refrigerant recovery, you can see why it’s time-consuming, as noted earlier in this report. Further, many recovery machines are not designed for refrigerant flushing.

That explains why a lot of shops try to do the job with a gun and solvent flush, or even something like the Ford approved machine and flush. GM can’t tell you if that will work, and Ford certainly can’t tell you what its equipment does on GM vehicles. We can tell you that an independent shop that doesn’t do liquid refrigerant flushing is unlikely to be successful trying to fix this problem with a solvent flush and minimized replacement of parts.

Because a refrigerant flush is time-consuming, GM even requires dealers to get specific approval for it. And the fl at-rate time on the factory fix is about six hours (figure a lot more if you don’t do this job regularly, have to order parts, etc.), and that doesn’t include the flushing operation. With everything, this job surely can run over a three-day period. It can get very pricey if the vehicle is out of warranty, explaining why independent shops look for safe shortcuts and fewer parts replacements.

Sorry, we understand the issue, but the shortcuts have led to repeat compressor failures, and a new or even quality reman compressor is not pocket change.

GM only approves liquid refrigerant flushing if there was a catastrophic failure of the compressor or some other cause of oil contamination, desiccant bag failure, evidence of contaminated refrigerant (GM dealers have identifiers, and every A/C specialist should too) or a gross overcharge of oil. It’s backflush for most of these, but there also is a forward flush procedure (using a check valve that has been removed for backflush).  

Forward flush is just for contaminated refrigerant oil (with engine oil maybe?)  and/or contaminated refrigerant.

Otherwise, GM relies on such parts replacements as expansion valve or orifice tube, accumulator and certain hoses (and the condenser if necessary), plus installing the liquid line filter. GM also recommends a suction side screen in the compressor manifold. DENSO doesn’t approve suction screens, but it also doesn’t approve trace dye, and GM not only uses trace dye on the assembly line, but specifies adding it during this factory fix. We suspect that dealers will be installing the screen, and cautious independent shops should too.



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