It cycles when the low side is down to about 22 psi. I do use gauges. The pressures are normal based on my experience with half a dozen cars over the years. It seems to cool quite well, much better then I expected with 134a. It's a weak system as designed, always was even when brand new with R12. Too much interior volume, too little AC capacity and airflow.
Yup. The pump was one of the best $100 investments I've ever made. Pulled down to 29 vacuum and pumped for about an hour, then checked and it held vacuum.
Everything is new. New compressor, new condenser, all new seals, new orifice tube. The only old parts are the evaporator and a couple short pieces of hose... which didn't show any restrictions when flushed.
On Sun, 18 Oct 2015 12:44:29 -0700, "tony944" wrote:
The system MUST be purged before recharging, partigularly when switching refrigerants. If it has an orifice it must be removed and checked - preferably replaced AFTER purging the system with nitrogen. If it is an expansion valve system I'd take a real good look at the valve and check function. If the system has been open any length of time , the receiver-drier should also be replaced. Then the system should be totally evacuated and held at a deep vaccuum for at least an hour, then the service valves should be closed and the system left for an hour or more- check for loss of vaccuum. If the system proves to be sound, install the r134 conversion valves on both high and low pressure sides, Charge to the low side with the specified amount of Ester oil. PAG is also used with 134, but on a conversion, in particular, Ester is better as it is les hygroscopic (it has less of an affinity for moisture). Then draw in the proper amount of R134A.. Proper fill is aproxemately 65% of the R12 charge.. A 75% charge is USUALLY an overcharge. On systems with an orifice tube, for conversion I REALLY prefer the automatic (AKA Smart VOV) tube. If not, the blue Ford tube works best for 134 in a conversion (even on a Chevy). I installed AC on my 1996 Ford Ranger, using the hoses, compressor, receiver and evaporator from a 1993 with the condenser for a '95. I put in the smart VOV and charged it to 1994 R134 specs (36 oz) - and promptly blew the overpressure plug. I then checked several other sources and found out the published spec was WAY too high., so I used the 1997 spec (22 oz), which ended up being just over 65% of the
1993-R12 spec. (32 oz) which would be 20.8 oz. Ford specifies PAG oil for R134A, but I use Ester because it is compatible with the old mineral oil - and on a conversion, there is ALWAYS a possibility there is some mineral oil remaining in the system- no matter how careful you are. It is also safe to mix with PAG.
PAG is NOT compatible with chlorinated refrigerants - like R12 or R22. It will turn to thick brown mud upon contact with R12..
Perhaps that is the OP's problem??? The "mud" will plug the expansion valve/orifice and cause the high side to go nuts. It might allow the system to work well for a day or so before plugging the orifice - and then blowing the system on restart.
It's been 3 summers now and it cools perfectly.
Like almost everyone else has said, it could be an intermittent restriction in the high side, but that seems unusual, especially if you see nothing in the orifice tube.
I would be inclined to replace everything that controls the cycling - high & low side switches, and the compressor relay - whichever of those your vehicle has, just in case they are intermittently stuck.
Pretty strange problem. I guess there could be a large-ish piece of metal or something floating around that blocks a passage every now and then. If you could catch it when it's acting up, and you have a pyrometer, the high side is going to be very hot ahead of the restriction, and then cool right after it. So if the liquid line is cool before the orifice, it's probably going to be the condenser. There could also be an issue with the compressor hose assembly. And now that I think of it, a restriction in the low side would do exactly the same thing, but that would show up clearly on the gauges. Anyway, good luck with this one if it is a restriction, unless you can find where it goes from hot to cold while it's happening.
There are almost no original parts left, the only significant one is the evaporator. Everything's been flushed twice now since it originally had the mineral oil. It's had PAG46 since the first redo 4 years ago.
What would nitrogen do that isn't taken care of by the flush and pulling a vacuum?
I would like to have tried a variable orifice tube but the local AC shop who is also a huge wholesale vender as well as custom maker of hoses and such told me they see a lot of people who try them pull them back out because they malfunction in some fashion. Mine is a real pain in the behind to get to so I stuck with a fixed one.
I almost put r12 in it but I see from your post that would have not worked at all well with the PAG. Good thing I went with the 134a.
You said the R12 to 134a conversion is 65%. Every other thing I've read has put it somewhere between 80% to 90%. I used 85%.
Might want to check out this a/c pdf. It's pretty good. Scroll down to ~ page 34.
Thanks, that's a really good read.
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