R-12 to R134A conversion

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Hey folks, I hope all is well. I have been away from the site for a while but I am back now and getting ready to get this a/c system cranked up in my '76 Electra. Here is what I have brewing on my mind today:

The culprit: 1976 Buick Electra 225 Limited with a 455CI 4bbl V8:

This vehicle is equipped with GM's VIR a/c system which stands for Valves In Receiver, known as the EEVIR. There is NO accumulator on this vehicle whereas there IS a receiver/drier that is in combination with the desicant bag to absorb moisture. The only sensor that this system uses STOCK with R-12 is an evaporator temp. sensor. There is also something called a thermal limiter fuse which is a three wired connection and has a "fuse" or better yet BREAKER installed in the connector. I am converting to R-134a and here is what I have done thus far. I am being told different things from a/c "pro's" on the chat forums at ackits.com where I purchased all of my conversion hardware for the system and I am in need of understanding the CORRECT way to do this......

I have taken all my lines off and flushed them with brake parts cleaners and blown them out with compressed air. I have flushed the evaporator and condenser the same way and blown them out. I have installed a BRAN NEW EEVIR receiver/drier with the new, I think it is xh-7 or xh-9 dessicant bag rated for R-134a as opposed to xh-5 dessicant for R-12. The WHOLE assembly is bran new and connects right up to the old fitting and looks JUST like the old one. I have replaced every O-ring where I have broken a connection at a line fitting and lubricated them with the bav/pag oil. I drained my compressor as best I could and replaced the O-rings that the lines mate to as well as will be refilling the system with 10.5 oz of bav/pag oil. I am using the old refrigerant lines that are in perfect shape as far as I know and I have NOT purchased or had BARRIER HOSES made for this car. Is this a mistake or will the molecular diffusion of refrigerant through the hoses in an R-134a retro be negligible? I will know the system integrity when I initially pull a vacuum on the system for evac and leak detection.

In addition I have removed the schrader valves from the old R-12 fittings and then screwed on and tightened the new R-134a connection fittings over these old valves on the high and low side. The new connections have a valve in them so you must remove the old valves from inside the old fittings because if you dont, you are double valved and it will not work. Then, due to the nature of this conversion, the high side line retro-connection fitting has a T-connection where you hook in a HPCO(high pressure cut off) switch. This switch is a two wired connection and everything I read tells me that I just wire the switch in series with the main power feed line (positive power feed) to the compressor so I did.

That is what I have done thus far, I am waiting on my vacuum pump to show up and then I should be close to charging time after evacuation and vacuum leak detection testing.

My questions thus far:

My high pressure switch right now is in open loop, with no continuity at NO pressure. In other words, my compressor will not engage at this point with no pressure in the line the way I have it wired. I would assume this is correct and that once I begin to charge the system, the pressure from the refrigerant charge will allow the compressor to come on and pressurize the system until it reaches a higher pressure at which point the switch will go into open loop again?? Or is it possible that I may have to jump that switch at the first charging to build enough pressure for it to function as designed? In other words, it seems that this switch is a low and high pressure switch. If there is NO pressure it is open loop so the compressor won't run and burn up I pressume. With some pressure it closes and allows compressor engagement and then at a higher threshold pressure, she'll open loop again? Or am I wired wrong,LOL?

Also, everyone has been really helpful on the a/c forums chat room but one guy told me that VIR systems, if working correctly, do not need an evaporator temp sensor. My car is a VIR system and it is STOCK with a temp sensor in the evap box under the hood. I am getting confused because I don't understand that. Keep in mind that my system on R-12 ONLY has a temp sensor, NO HPCO switch. Therefore, that is the only switch that would sence that the evap is cool enough and therefore, kill the compressor when she is running on R-12. Why would this evap sensor not be needed when it was the ONLY sensor in the equation from the factory when the system was running R-12? I think he is full of shit! The only potential problem I can see now that the conversion has been done is that the addition of an HPCO to the system in conjunction with the "in place" evap temp sensor is: what happens if my pressures build in the lines to the point that the HPCO I installed decides to kill the compressor, yet the evap is not cool enough yet? I am basically using two sensors now to do the same thing it seems and that seems like there is the potential to have one confuse the other. Perhaps with an HPCO, I do not need the evap sensor and will have to jump it permanently, or no?

This same guy that told me that a good functioning VIR system does not need an evap temp sensor told me that VIR systems that have been converted and that work well are out there, but typically they are harder to get to work satisfactorily than others. Is this true? Am I pissing up a rope trying to do this because I don't fully understand it? I don't think so because he is the first to tell me that. I went to the people that sell the parts such as the VIR before I got into this and they make the parts for that car for the conversion and no one told me, oh this won't work well. Any ideas please? Thank you for your time!

Could someone, IE) VWHOBO PLEASE shed some light on this?

I plan on charging the system more with vent temps and gauge pressures than with how many oz's of R-134a, but does anyone know the charge amount roughly? I have been told 45 oz of R-12, so start off with maybe 60% of this in R-134a and then watch pressures and vent temps. Also, does 10.5 oz of oil sounds about right? I believe this is the A6 compressor as I have been told, but on the sticker on it, it is a MURRAY compressor. It looks like a long cylinder but when I took it off the car she's got what looks like a V8 oil pan underneath which I assume is the crankcase. I don't specifically see a drain plug though and really, I only got a few drips of oil out of it. Should I re-remove it and drain it another way? I need to make sure all the oil is not trapped in there somehow.

Thank you for you time reading all this. I am sorry it is so long but I am EXTREMELY detail oriented and I need to type is all out so you can understand my scenario and problem. I want my air conditioning to work well and I want to do it correctly the first time. This is a learning process for me. Thank you, again, for your help with this!! :thumbs: :thumbs:

posted by  cmeseadoin

If you have a receiver dryer, you probably have a TXV with a sense bulb on the suction line near the evaporator If it has a suction line accumulator, then the car will have a orifice as to meter the refrigerant without a sense line. In the case of your Electra, if it has an expansion valve (TXV) with remote bulb and receiver-dryer, it needs to remain that way

Many GM's either have separate high pressure and low pressure cut-out switches although some have a combination high-low pressure cut-out. The actual configuration varies from model to model and from year to year. The low pressure cut-out or combination switch will have to be jumpered out during evacuation and while initially charging the system. Without a wiring diagram for the car and the schematic for the switching, I can't tell if it is wired right or not.

You need to evacuate the system and hold 500 micron or lower vacume for a couple of hours. This low of vacume or lower flash vaporizes the moisture in the system

R-134a does not diffuse any worse than R-12. If the hoses are rotten after almost 30 years of service, they will leak refrigerant regardless of the type used

You need to obtain a set of refrigerant charts or Mollier diagrams for R-134a to detrmine what head and suction pressures you should expect. Expect the supply air to be a little warmer due to the properties of R 134a since the I did not notice in the post if the expansion valve has been replaced

posted by  tbaxleyjr

This should be a very interesting response. Let's all see just how stupid seemee tries to make you feel "tbaxleyjr", when he is wanting HELP. Watch how nice he is :laughing: You#@*$#@:doh:

posted by  lectroid

I do actually have a receiver / drier. I actually have what is called an EEVIR (evaporator-equalized valves in receiver) assembly which I stated in my original posting. Just so that you know I am not full of shit, here is a DIRECT quote from HAYNES AUTOMOTIVE HEATING AND AIR CONDITIONING manual:

"The Valves-in-receiver(VIR) unit combines the functions of an expansion valve, a POS STV and a receiver/drier into one assembly. The VIR is usually installed near the evaporator. In a VIR unit, the temperature sensing bulb and capilllary tube for expansion valve are eliminated because the diaphram end of the expansion valve is directly exposed to the refrigerant vapor entering the VIR assembly from the evaporator outlet."

So what do you mean that "If I have a receiver/drier, that I have a TXV with a sensing bulb on the suction line????" I am not trying to be too hard assed, but I am not so sure you know A) what I am talking about or B) what you are talking about.

I can understand this, however, if you know anything about this car, I AM TELLING you that there is/are NO other switches in place with the FACTORY set up for R-12 other than the evaporator temperature sensor that reads ambient temp. of the evap. There are NO other switches installed from GM. Part of the conversion is the installation of what is called an HPCO (high pressure cut off) switch. I was trying to determine, based on my description of it's operation, how that switch works. It is open loop with no pressure and goes into closed loop WITH pressure. So you can re-read my posting because it is too much to re-type on how that works. I have got to install that switch to read pressure but I wanted to confirm that those HPCO's work by being open at no pressure, closed at pressure X and open again at some higher pressure X+Y where Y is some higher number??

500 microns???? All the vacuum pumps I have been looking at pull to a max of 50. I think you mean more like 20-25 microns where maybe it is more accurate to talk in inches of vacuum. perhaps 27-29 inches of vacuum??

Really? Everything I read tells me that chemically, R-12 molecules are larger than R-134a molecules. Are you sure you are leading me in the right direction? I believe my hoses are in good shape as I have inspected them, however, the real test will be the vacuum application. But I don't think you made a correct statement in the fact that you say "R-134a does not diffuse and worse than R-12." I do agree, however, with the latter statement.

Thanks, I was asking if anyone knew the pressures. If I had the answer in front of me, I would not have posted the question.

I appreciate your efforts to help me but you are talking to someone that knows quite a bit about cars and a/c yet I have just not done a conversion before. So I was looking for a little more specific information based on the post that I took an hour to type. I happen to think that you are not exactly making some of the most correct statements either based on what I know and what I have read. Thanks though.

posted by  cmeseadoin

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