My factory ac 66 has had the STV valve removed and replaced with a pipe. I want to put it back. My question for the experts, should I gut the STV and just put it in with the newer style electric switch that cycles the compressor or go ahead and get it working again? Is it colder with the STV or does it not make a difference? My STV has the atmospheric pressure valve still attached. I highly doubt that is working. I would like to leave it attached however I am worried that it might leak. Can this be blocked off in some way? The manual shows a seal between the two valves , it looks like a little sleeve. None of the kits have this and I don't see it for sale anywhere. I also have the original expansion valve. It has been left open for years and is pretty cruddy. I can clean it up and test it. There was a very involved test procedure somewhere that I can't seem to find. Can anyone steer me in the right direction? I know a lot has been written about this, I am looking for the latest perspective, a lot of time has gone by since a lot of this was written. BTW using freon 12. Thanks

 

Just replaced the STV on a 64 AC Coupe with the Electric Conversion. It works great. Also converted to R134. Blows cold here in the Vegas 110* heat.

 

Any chance you could provide info for the vendor of these electric conversion parts ?
Thanks
Ted

 

https://www.zip-corvette.com/63-66-a...pdate-kit.html

Update kit eliminates problems due to a sticking valve or bad diaphragm by converting OE valve to more reliable cycling clutch system. Delivers improved air condition performance yet maintains original appearance underhood

 

Thank you. Been struggling a bit with my factory air coupe. One of those things where I'm not really sure what the PO has done to it. Supposedly converted to R134A.
Appreciate the quick response.
Ted

 

Above you said R12?

You can tell by the fittings on the compressor R12 and R134 are different fittings.

These are R134 Fittings

 

I have to apologize, I've kind of hijacked the OP's thread. He's the one that's been using R-12. Yes, I'm aware of the difference between R12 & R134A fittings. The PO of my car had one R134A fitting adapter installed. All other fittings are the old R12 fittings. Have no idea if the oil was changed either, so I'll probably evacuate the system and start from square one.
Thanks
Ted

 

If y'all are running the original style A6 compressor, that last thing you want (for long life) is a cycling clutch system. The old A6 wasn't designed to be constantly turned on and off at speed...do some investigating.

 

Haven't seen any comments on warning not to use electric STV replacement. I understand OME and NOS STV's are not available so electric seems to be the alternative but not if it causes A6 to fail. I can replace other components but stuck as what to do about STV. I have a new to me 65 roadster with factory AC, I have no idea when it last worked but need to get it functioning. Prefer to use original parts or replicas and will add update condenser to work with R134. Any suggestions welcome.

 

Hi Johnc, There is a host of information on the factory air conditioner on C2 corvettes. What it amounts to is does your car still actually have the the original valves? If so are they in rebuildable condition.? And lastly do you have the skills and patients to mess around with them? The expansion valve is not rebuildable. There is an off the car test procedure. It is fairly involved. Powershift and EMdoller on this forum can steer you the right direction for testing the valve. If you are not going for full points you may be better off to getting an aftermarket replacement. I recommend getting the one with the hook shaped sensing bulb. If you still have the STV the diaphragm and seals are available. The piston is not. If the bore is scored or the piston has imperfections the valve is scrap. If they look ok there is a very comprehensive set of instructions in the shop manual. You will need some Molykote Z or equalivelent and buy the diaphragm kit, costs 86 dollars. There are two diaphragms available, the most correct one has a small extrusion at the botton, the other one is smooth. Original Air has the one with the extrusion. That more closely matches the original. You should also take a look at the AVR valve, this is the little valve that is screwed to the side of the STV. It is easy to test with a few tools, a hand held vacuum pump and a vacuum gauge is all that is needed. The procedure is in the manual. If it does not work they are NLA and cannot be repaired. If it fails the test just shove a ball bearring in the vacuum hose and forget it. The AC will go to full cold, not compensated for altitude. If you regularly dive at high altitude you may need to make a slight adjustment to the STV to compensate for the AVR being disabled. You will also have to make an adjustment the the STV if you convert to freon other than R12. I kept R12 in mine but it is not an inexpensive option.There is no freon present in the part of the STV where the AVR valve is connected so you will not get a freon leak if the AVR is bad. If your valve STV is not rebuildable you will have to go with the update kit. Don't get the one with the pipe, I suggest that the kit with the plate that blanks off valve internally, the valve looks the same it is just no longer functional and you will have to put in a cycling switch to cycle the clutch. The A6 is very robust, it can take the cycling for many years. It's not ideal but you don't have a choice at that point anyway so go with it. Obtain the shop manual, it is very comprehensive. I will be happy to help and the forum has some real experts.

 

I converted my 67 to R134A and also replaced the POA valve (somewhat different from your STV) with the cycling type. I hated it, the cycling was very noticeable. So I had my original POA rebuilt for R134A and am very pleased with it.

 

The POA seems to be a better set up and much more available. Not an option wit a 66 or earlier.

 

Unless you install a 67 evaporator core in your 66 car. .

A few have done this...........

LARRY

 

I have a brand new factory fresh a/c evaporator still wrapped up in the factory shrink wrap. I snagged the last one from LIC. I have the STV and I found a NOS piston on E-bay. The original expansion valve tested out ok (Thanks Powershift and EMDoller). So Im sticking to the 66 stuff. I did not know that you can change out the evap core and use a POA. Very interesting. I am not working anymore on the AC, it is blowing cold with the pipe and switch set up. Next year I plan to pull out the engine and restore the engine bay. Once it is out I will redo the entire A/C back to factory. Collecting and rebuilding parts along the way. Im keeping it R12 which is probably stupid, green o rings and barrier hose in case I change my mind. I still have about 14 lbs of 12 left, should last my lifetime which grows shorter with each passing day!

 

For educational purposes....
The A6 tolerates cycling as long as the clutch is up to it. My 78 Caprice used a cycling A6 compressor.
However in general you are correct. The beauty of GM factory air in this period was its constant compressor operation with suction modulation, first with hot gas bypass, then suction throttling valves (STV) and after that pilot orifice absolute valves (POA). These all had one hallmark when they worked right, smooth consistent operation, no temperature swings or compressor in and out to be heard or felt. The downside was complication. The hot gas bypass leaked. The STV would stick and be in use only 4 short years. The POA was a good solution but looming fuel economy standards made easy work of throwing away the POA for a new design featuring a cycling compressor.

The STV and POA eliminator kits work. I run two of them. They replace the throttling valves with an open pipe that allows the system to run at full throttle and controlled by a snap action switch tied to a thermostatic capillary tube. It is quite imperfect with wide swings between compressor reengagement. In both cars I've shorted the switch and manually cycle the compressor to keep the evaporator from freezing. I find I can keep the car far more comfortable than the rinky-dink T-stat.

The A6 clutch for STV & POA systems was not designed for high duty cycle operation especially at high RPM. Later cycling clutches were built for the on and off. The kit we are talking about turns on your compressor when it says so and at high RPM highway cruising it will smoke in due time.

The GM refrigeration system works much better when it works as designed. If you have the patience to get an STV or POA to function to spec you will be rewarded. The kit, and there is really just one made for a host of GM cars, results in operation well short of that intended. It will make a lot of cold, but still well short.

Dan

 

Dan:

A good explanation for many.



Larry

PS: My 1978 Z/28 Camaro had factory air with an A6 compressor that cycled with suction pressure. It lasted over 80,000 miles without replacement. I sold the car at this point, so I can't comment on how long after this it continued to work.