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A/C Question

rockfoot

rockfoot

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Location
Moncks Corner, SC
I have a 1997 6.5 suburban with dual A/C. I am not sure that I am in the right place to ask this question. I am in the south so it is hot and humid. At 4pm, about the hottest part of the day, I put the gauges on the A/C system. Low side was 70 psi and hi side was 250psi. The system has not been putting out as it should for about a week. There was no condensate on the suction line. I put in enough 134A to make a difference (5ea.10 second shots of liquid from a 30#bottle) or at least to cause a change in the pressures. The pressures did not change. The air coming out is somewhat cool but the suction is not coming down. I ran the back system by itself and the front unit by itself and then both together... no difference in the pressures. I suspect a bad or weak compressor. What say ye???
 
Rev the engine up and what do the pressures do? 70 PSI is 70 degrees. This is a high low side condition. Maybe the compressor is bad, but the bigger question is why? Usually they knock or leak.

Do the gauges flutter? Anything but a rock solid steady reading is flutter. This would indicate a failed valve or debris in a valve cutting compressor capacity and leaving you with a high low side.

Air in the system can also do what you have. (But not flutter.)

The dual air systems as a rule should never have the rear fan speed set below medium with the AC on due to possible expansion valve failure and wiping out the compressor over time. Not that these units were that reliable to begin with.

Some info on the dual system design although the TSB may or may not apply.
http://www.thetruckstop.us/forum/sh...fo-Yes-it-has-a-Thermal-Expansion-Valve-(TXV)

Should the compressor be bad:
Replace it.
Flush the system.
Replace the orface tube.
Replace the accumulator.
Replace the expansion valve. (a PIA, but trust me it needs it.)
Possibly install a liquid line filter depending on the amount of debris in the system.
Consider replacing the condenser as they can't be flushed very well. Again depending on how much metal is in the system.

Add the correct amount of oil.
Pull a hard vac on the system.
Add refrigerant by weight. 4.0 lbs for 1995 - your year may vary.

The only way to get the correct charge in the system is to pull a vacuum and charge it by weight. Too much charge by the guess the amount can blow stuff up or just not cool really well. Too little and the compressor starves for oil, puts a bunch of metal trash in the system and then locks up. lots of folks add just enough R134a to cool well and stop. they then have the compressor start knocking on them and have a real mess to fix. The system leaking down also causes this failure. So does a stuck open TXV destroy a compressor in this system.

In other words just adding freon is a waste of your money and can cause trouble. Have it sucked down and charged properly. In your case repairs looks to be required anyway.
 
I would be willing to help you diagnose the problem.

I live less than a 1/2 hour from you. You could pm me and I'll give you my phone # or you could list all that you have done to the AC system.

Did you change the orifice tube? I need to know what has and hasn't been done to make an accurate diagnosis.
 
FWIW: The orface tube and accumulator are the "oil filter" of the system along with other functions. Skipping them with a compressor swap is like replacing a failed engine without replacing the oil filter. It also voids the warranty on most compressors I know of. There is always something in the orface tube screen. The flushing of the system removes old contaminated oil and other wear metals. This allows the compressor a long life in a clean system. The expansion valve also has a screen. So does the accumulator. Screen = oil filter.

The above recommendation is not to just throw parts at something. It is to do the compressor replacement so the replacement will last.
 
The flushing of the system removes old contaminated oil and other wear metals. This allows the compressor a long life in a clean system. The expansion valve also has a screen.
Click to expand...

^^^ Exactly^^^

It failed for a reason and just changing the compressor only makes it worse. Without flushing the system the expansion valve in the rear and the orifice tube will become clogged with the debri of the old compressor and now you have even more work, because not only will you have to replace the E/V and O/T, the new compressor will be chewed up by the debri and the warranty will be void on it unless you can prove the system was flushed before said installation.

If this hasn't been flushed, do so before you take out the new compressor and fill the system with even more debri.
 
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