I recently rebuilt my entire A/C system and converted to R134 . new drier, evaporator, compressor, o-rings. used existing condensor and lines. Had my mechanic flush-clean, do the vaccum test, and recharge. Worked great for a few weeks . . .. but
During the extended test this past week, on a road trip thru PA - Maryland - VaBeach and back, after about 6 hours of use in extreme conditions ( 85 degrees - high humidity - really hot out) the belt started squealing, a little at first, under load at speed. I let it squeal for awhile, say half hour, stayed cold, finally decided to give it a rest - figured it needed belt tighteneing.

Next morning, with engine cold, I tightened belt some, started up, no squeal, works fine. Took off - about 20 minutes later after things heated up. started squealing. Bought a size smaller belt to get more tightening room, and got it real tight. Now it really squeals, I notice the compressor pulley jerking, like its threatening to sieze. Whoa. Thing just did NOT want to turn.

I left the A/C off the rest of the trip. I figured it must just be a bad compressor. I want to get a refund and another compressor from NAPA, but before I do that:

1) Are 'bad rebuilds' common?
2) Shouldn't the compressor perform well under even extended heat conditions?
3) BIG QUESTION: Can't I up-grade, to a later-year compressor design, i.e. retro fit a newer-technology compressor to this old system?
4) If not, are NEW A6's available? Or am I stuck replacing compressors until I get a good one?

Incidently, I got the A6 WITH the superheat switch, and got that circuitry to work, however, it never kicked off, probably because I stopped using it (hopefully) before it did any damage to the rest of the system . . . ?

It would be nice to just drop in a later model compressor, which may actually run more efficiently. I do not care about NOS. I just want it as cold as possible. It got plenty cold with the A6, but for instance, in my toyota, when I turn on the a/c, it gets freezing. I wish the old vette would get that cold!

 

1. Yes, unfortunately, bad rebuilds are very common.
2. An A-6 compressor should run for extended periods in very hot weather.
3. The R-4 (R for radial, the design of the pump, A is for axial) became standard in Corvettes about the late 70's, and by early 80's all GM. The swap in your car should be easy provided you can find a set of brackets from an 80's truck with a BB or search for a company that makes the brackets as a kit. The latest Corvette AC compressor (Sanden) is an excellent unit drawing less horsepower than the A6 or R4, however brackets may be an issue.
4. New A6 compressors are available through GM and distributors. At over $400 it is steep but more reliable than rebuilts.
With the problem you describe (R134, quiet when cold, squealing when hot) you may have too much R134, it produces higher head pressures than R12 and as temperature across the condenser rises, head (or high side) pressures rise. The high pressures cause too much pressures against the small cylinder diameter of the A6 piston making it fight the pulley and clutch. Try reducing your R134 charge by an ounce, or verify with gauges after running for 20 minutes.
Hope this helps.

 

2)
3)Not sure the pulleys will line up. 454 truck went from A6 to sepentine so brackets are a big issue.
4)


[Modified by markdtn, 12:18 PM 7/6/2004]

 

Thanks Missileman . . . now I am kinda p'd I didnt know this, I could have tried venting some pressure via the schrader valve, it might have allowed me to run the a/c on the drive north from VaBch up 13 . . . it was brutally hot. I just ran the car for an hour today, it wasnt squealing and stayed cold, but the temps today are milder compared to last Saturday. I will remember this next month when we do Nags Head.

 

From your description there is nothing wrong with your compressor. The stock '73 system uses a POA valve that vents (bypasses internally) excess pressure when it reaches a certain point and thus allows the compressor to run continously without building pressure to the point where it wants to lock up. Also, the expansion valve is in there as well. The fact that it works well after not being used would suggest that is the problem to me. To test this, re-tension the belt to the proper setting (a bit looser) and run it 'till it starts to lock up. turn off the A/C for a few minutes with the engine running, then re-engage it. As you do this, put a temp indicator (dial thermometer works go for me) in the center register and see where the temp is when it starts to sieze. If it goes much below 34 degrees it's freezing up the core with condensation and that will over-pressure it. If it works again right away, the compressor's alright.

A set of gauges on the system is the best way to check it out, so you can actually watch the pressures. I just did a '73 SB and the first POA valve we got from Zip was defective, but they made it right in short order and it now works great. Good luck.

 

A quick thought on replacing the A-6. The new ones do work very well, but you have to set it up as a pressure cycling system. That's actually easy, but the downside is you can feel the clutch kick in and out as you drive. Most folks actually don't mind that and it is a simple solution.

Hans

 

The A6 Compressor when it is new is about as good a compressor as there is. Unfortunately 95% of the rebuilt A6 compressors are junk. I'd suggest spending the money and buy a Sanden compressor and the hose adapters to install it.
Check with Hot Rod Air and see if they can set you up with a compressor that will work with your system.
http://www.hotrodair.com