ptt

1990 AC green o-rings

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ptt    19

I'm getting ready to recharge my previously converted to r134a 1990 AC system and have the green set of O-rings for the job.  My question is do these green O-rings require some silicon on them when installed?  I recall doing that in the past but I'm not sure it was with green O-rings or even with r134a refridgerant..  I think the r134a refridgerant is smaller sized moleculer-wise and whether or not that would require the silicone to achieve a better seal at the O-rings may be the case.   

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Barney Eaton    521

I just wiped them with the oil for the 134, I believe the only need to do anything is because they are dry when installed and you want them to slide in place....not tear.  Once in the operating system they will get oiled

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drtidmore    223

I can't say if you need to lubricate them or not but I did not do so when I did my compressor replacement and conversion to R134a almost 4 years ago.  What I did do is use R134a WITH a leak stop agent additive in the R134a.  You are correct about the R134a molecule being smaller and therefore more difficult to seal.  I pulled a hard vacuum on the system for 12 hours since the entire system had been opened up and then I closed off the vacuum pump and monitored for vacuum leaks.  No leaks were indicated after several hours, so I moved forward with charging the system.  Despite no leakdown of the purging vacuum, the initial additions of R134a managed to find leak(s) but the leak stop agent did its trick and I was able to move on and complete the charging.  I have had ZERO leaks since the time of my conversion.  The trick is to monitor the pressure levels on the system as you add R134 and not just depend on the amount alone as an indication of success along with how the low temp sensor is behaving (diagnostics).  You want the low temp sensor to hover right around zero to 1 and not wildly swing between -2 and 9 on the highway (that is an indication of too little R134a in the system BTW).  It may take several adjustments in the amount of R134a to get an ideal charge but it is possible using the AC low temp sensor alone.

Edited by drtidmore (see edit history)

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ChrisWhewell    86

I didn't change my o-rings at all. Too much of a pain to hunt down, the people at local FLAPS generally have putty for brains and I remembered the last time I changed o-rings, took about a week to get everything right. Its been one year, no problems, AC blows cold. I'll add that I have a compressor problem, the low side pressure is waaayyy too high, and the system when running will only accept one 12 oz can of R134a before the pressure release pops. So, I'm running old o-rings and about half a charge but that's all she'll accept and it really blows cold. I'm perplexed. Also, R134a is not smaller than R12. 134a is tetrafluoro ethane, a two carbon backbone whereas R12 is dichloro-difluoromethane, only one carbon atom. both are halocarbons and the only diff I see that might matter is that R12 is a bit more polar and should only be an issue for seals when water is present in the system. If you keep it dry, use a new dessicant, etc., the old o-rings should be fine is what I suggest. Even though there are others with different opinions, that's what I see.

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drtidmore    223
42 minutes ago, ChrisWhewell said:

Also, R134a is not smaller than R12. 134a is tetrafluoro ethane, a two carbon backbone whereas R12 is dichloro-difluoromethane, only one carbon atom. both are halocarbons and the only diff I see that might matter is that R12 is a bit more polar and should only be an issue for seals when water is present in the system. If you keep it dry, use a new dessicant, etc., the old o-rings should be fine is what I suggest. Even though there are others with different opinions, that's what I see.

In researching the matter of R134a there is virtually unanimous consensus that R134a is smaller.  However, there are some that share what you have stated, so it would be nice if this matter could be put to rest.  What is agreed by all is that the R134a's molecular weight is smaller that R-12, which may be where the confusion initially started. 

It is generally agreed and I would say, in alignment with what I found when converting, that for whatever reason(s) R134a has a propensity to find points from which to leak at a greater level than R-12. 

 

As for your WAAY higher suction side pressures, that typically points to a plugged orifice.  

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89RedDarkGrey    271

Maybe it's got something to do with the different oils used (mineral, PAG)? I think it's also about the composition of the O-ring material itself- not cooperating with the new oil and refrigerant combination- exactly why my Friend Dave (HVAC Tech) chooses to use the PC duster, as he states it's much closer in all ways to R-12 for capacity. The proper O-rings are easily obtained from RockAuto no need for FLAPS putty brains:lol:

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ChrisWhewell    86

there is a lot of misinfo out there, look at this link below, they have the illustrations for R12 and R134a reversed. If people don't know the difference between a methane and an ethane molecule, they should shut up about chem. http://www.rtsauto.com/how-to-recharge-the-ac-in-your-car-eg-used-will-be-e30-and-how-to-use-ac-manifold-gauges-and-pull-vacuum R12 only has one carbon atom, 134a has two in a chain to which the F's are attached. Never trust an AC tech on chemistry, these guys come to my house trying to sell me new units everytime they come out and think they can pull one over on me, until I start talking like I know their shitt better than they do, then they get disappointed. I got my BS in that subject in 87 from Hope College, if it matters. As concerns my orifice tube, it is clear, just was replaced. If you look you will find compressors typically show high low side pressure right before they fail. So, mine's due any day now to pop. I think if you look into it further you can find the reason why high low side pressure is not always due to a clogged orifice tube.

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ChrisWhewell    86

The size of the molecules shouldn't matter at all, I think the issue stems mostly from R12 being used with mineral oil as a lubricant, wheras with 134a you're using a more polar lubricant, typically erythritol esters, and the issue is whether the o-ring material that is designed to withsttand non-polar mineral oil, will stand up to the more polar erythritol esters. Probably both are fine, when pure. But these systems, no matter how hard you try, will always contain or generate some water due to normal operation. Its the presence of water that causes/catalyzes o-ring decay. Another factor is the plasticizer used in the o-rings. There's always many factors most overlook, you have to be a good detective.

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89RedDarkGrey    271

THIS VIDEO David made explains it better than I can. (the link cuts to the specific time of description). He is not a "Sales person" by any means, more of an HVAC Engineer at a Shop when younger. He now works in the Oil Field industry, and designs and maintains diesel engine control systems for offshore Oil Rig Platforms and levee systems around the world, mostly contracted by Caterpillar.

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drtidmore    223
On 5/7/2017 at 2:40 PM, ChrisWhewell said:

 I think if you look into it further you can find the reason why high low side pressure is not always due to a clogged orifice tube.

I stated that high suction pressure "typically" point to a clogged orifice.

Edited by drtidmore (see edit history)
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