I had my A/C system checked out by the shop, and they said to repair it, I needed a new compressor, Dryer and Diaphragm (along with the coolant). I have been considering changing over to a 134a system, but I want to replace all of the failing parts. I am familiar with everything but the diaphragm, where is the diaphragm located in the A/C system?

 

Beats me and I've been fooling around with GM a/c for about 30 years now. Ask 'em again. My guess would be they mean the orifice, which is in the high pressure line where it connects to the Evaporator - but they could have meant the Evaporator or the Condensor for that matter. If they're still calling it a diaphragm, find another shop.

 

Thanks, I will ask some more questions.

In the original quote, they list the dryer, do they fail? I just want to make sure that when I do order the conversion kit I get everything I am going to need to convert the system.

What are your thoughts on converting to 134a? Everything I have read on the forum suggests that the system will be just as efficient as the R12.

 

If im not mistaken the little diaphram there talking about it located near the rear of the engine inside the A/C line itself. I believe its a filter and i have replaced mine before. Its located near the blower just below the bent A/C line that runs to your condensor. if your unscrew the the connecting pieces you see the little filter inside. I think they only cost a few dollars. Im sure the more experienced people on this forum could explain it better.

 

Sounds like your mechanic might have sex on the brain, talking about a diaphram. I think he's talking about the orifice tube. That usually goes in the high side line before it gets back to the evaporator. He might have diagnosed a bad compressor because of noise or it might not be pumping right. Changing to r134 is the right way to go. If it is done right you won't notice any efficiency loss as compared to r12. It might even perform better. You will want to change the filter dryer and the orifice tube. Most likely, your guy is recommending changing the compressor because of the r134 conversion. R12 uses mineral oil and r134 uses pag or ester oil. None of these oils are compatible with each other and Mineral oil is not compatible with r134. I did a conversion a while back on my vette and did not change anything. We just repaired a leak, pulled a good vacuume and recharged with r134. It's still working, but I think I have lost some efficiency. I just did a conversion on an 84 chevy truck and installed a used compressor. I did allow the compressor to drain the mineral oil for a few days before putting ester oil in it. The air coming out of the vents is 40 degrees on a hot day. It sounds like he is going down the right path, but maybe not using the right terminology. I think you'll be happy with the conversion. Hope this helps. :iagree:

 

A conversion, done correctly, should blow 3 to 5 degrees warmer than the R12 that's in it. You need to get the old oil out and if the compressor failed, flush out any debris. Accumulators can fail and will if you put R134 oil in one that's had R12 oil in it. Pros recommend that they be replaced every 5 years; GM says they never have to be replaced unless there is a catastrophic failure or you change the gas. You will also need to get any moisture out by pulling a vacuum; otherwise the water can freeze and plug up the system. It will also destroy the compressor. General info can be found here: http://www.epa.gov/ozone/snap/refrig.../macssubs.html The site also lists web sites where you can get an a/c license to buy all the R12 you want if you'd like to stick with what you got.


[Modified by SunCr, 9:36 AM 9/10/2003]

 

I disagree with the statement that r134 will run 3-5 dregrees hotter than r12. According to the specs r12 is at 28.5 psi at 30 degrees while r134 is at 25.6 psi at the same temp. You can adjust your charge volume to compensate the low side pressure to the correct pressure for r134. I've had excellent results with the conversions. Like I mentioned before, My old truck blows 40 degrees at the vents so that's 30 at the evaporator.

 

No need to split hairs - 40 degrees is a great vent temp, but most who convert get a slightly warmer temp than what they had with R12 - especially in a Vette where the size of the condensor and evaporator are limited. GM sets the pressure switch at 25 psi for R12; you reduce to 22 psi for R134. Remember the switch is after the Evaporator. I blow 38 degrees with R12 up to about 90 degrees or so with 60% relative humidity; seriously doubt I'd feel the difference at 40. The point is the conversion works when done correctly.

 

I agree, you do it right and you'll be happy.

 

Oh Yea, I forgot to mention that that old truck is black on black and has a surface temp of 30 hotter that the cars around it. I am impressed it can work as well as it does.

 

By the way, the pressure switch is what shuts off the compressor if the pressure falls too low, below the minimum being 25 psi. At 25 psi, R134 is at 21.8 degrees. R12 at the same temp is under 25 degrees. Either way you evaporator will freeze up at those temps. If you shoot for 30 degrees at the evaporator, you'll get 38-40 degrees at the vents. If you get low on freon or if the ac is not working hard the compressor is designed to shut off. That is why your ac compressor won't kick on if you are very low or out of freon. This really has little or nothing to do with the working temps/pressures that your are shooting for on the evaporator.

 

These conversions are still not an exact science. I found some more interesting information on conversions. I read some articiles that indicate smaller orifice tubes for r134. Maybe that's why the old truck works so good. I also found some variable orifice tubes for about $20 that are supposed to compensate the refrigerant flow for idle vs crusing. Supposedly they were tested in the desert and had increased performance over fixed orifice tubes. I think I'll try one of those on the blue vette before it goes back on the road.

 

the orifice tube is very important when converting. use the "blue" orifice tube when you convert. the stock one will work , but wont cool as well at idle.

 

Why not get your license and keep it original? R12, if you shop, shouldn't set you back more the $60 to $75. Try Autozone, it was about $15 a can though I found some selling it for $10 a year and half ago, so I bought a half dozen. None of the 4 stores I went to priced it the same. A license is 25 bucks at http://www.epatest.com or any of the sites listed at the EPA web I previously posted. Also, for more info & dialogue about conversions and automotive a/c, go to http://www.ackits.com and sign on to their board.

 

Actually, I am MVAC certified along with other certifications and degrees. R12 is too hard to find. It is damaging to our ozone layer and R134 is actually more efficient than R12. They don't even make R12 any longer. So if you can make your system perform as well or better with r134 than R12, what's the point of keeping R12. The old truck I just did got a new orifice tube. I would imagine that along with the correct charge is making the biggest difference. I wouldn't ever go back to R12. I am hot natured and I have to turn down the ac in the truck sometimes.