Hi Martin, I realize you asked this a month ago, but I don't think anyone answered it yet. So I'll give it a try: Sorry, the explanation is long but nonetheless educational. The compressor cycles on & off in order to maintain pressure behind the expansion orifice. The end result is that when this pressure gets low enough then the compressor cycles on, and when the pressure is restored then it cycles off. This is an intuitive way to look at it, but the process actually works in reverse. The pressure switch that controls the compressor monitors the low-side pressure to keep it at a range of between 28 to 32 psi. This design assumes that if the low side is this low then the high side pressure behind the expansion orifice is at the proper level. When the compressor cycles too quickly, this is usually a symptom of too little refrigerant in the system. Before the high side can reach a reasonable pressure, the compressor has already sucked the low side below 28 to 32 psi causing the compressor to cycle off. Knowing that a healthy system should cycle for approximately 45 seconds at idle or for about 7 seconds at 2500 rpm, stupid people try to force the system to behave this way by adjusting the low pressure cycling switch rather than finding the cause of the problem (probably too low on refrigerant). The only proper adjustment for this switch is to have it cycle within the 28 to 32 psi range regardless of cycling time. Now Martin, in your case you are using a R-413 (yes, not a typo guys), and I don't know how this should behave in a system designed for R-12. I know that a system properly converted to R-134a will have cycling times similar to R-12. But R-413 may be a different animal. An ideal R-12 alternative should produce similar high side pressures for a given low side pressure of 28 to 32 psi. R-134a comes close. It produces high-side pressures a little higher than R-12, and this is one of the disadvantages of R-134a because people worry that the extra pressure could cause a leak or wear out the compressor faster. Not knowing the characteristics of R-413, I can only offer the following advice: Make sure that the low pressure switch is cycling within the proper range. At this low side pressure, check in the DeLorean Workshop Manual to compare with the corresponding high side pressures (while considering the ambient temperature) to make sure that the high side pressure stays within a reasonable range. If it is too low then add more refrigerant. If it is too high then remove some refrigerant. If you can maintain the high side pressure within these specs AND the cycling time is still too short then consider the compressor's duty cycle. If it stays on for only 3 seconds at a time but cycles at a slower interval than an R-12 system then you have a really incredible refrigerant, but I doubt that. Maybe there is some other problem in the system allowing the high side pressure to bleed down too quickly. Maybe the orifice is too big. Maybe the o-ring(s) sealing around it are damaged. I would not suspect a clog unless the system was cycling on the high-pressure safety switch (in which case your high-side pressures would be way too high). Your system may or may not have one of these safety switches. Early VINs don't have it. Intermediate VINs have the switch at the bottom of the condenser. Later VINs have it just before the expansion orifice. > When he gassed the system, the compressor engaged for steadily longer > intervals, Yep, that's how it works. > but he had put the correct amount in and didn't want to put > any more in. So what is the correct amount? Is it the same 2.2 lbs recommended for R-12? The recommendation for R-134a is to use 80% to 90% less. Maybe his R-413 bottle got too cold to boil and he didn't have enough patience to get the full amount in. Did he use a scale to weigh it? > The blowers are freezing. Well at least it works. But maybe the refrigerant is flowing too easily. > Perhaps I need a new accumulator? First some background: The accumulator's job is to function as a refrigerant storage device. It receives spent refrigerant from the evaporator and holds any remaining liquid refrigerant returning only vapor refrigerant to the compressor. (Any liquid getting to the compressor may damage it.) It also contains a water absorbing desiccant to keep the system dry. This is the only part of the accumulator that can wear out. Once sealed and charged, the system should not get any more moisture in it. It is my opinion that the accumulator should be replaced any time the system has been opened up. Usually people who think otherwise are mechanics who are cheap & lazy or who don't want to risk problems. Replacing them on the DeLorean can be tricky and destructive to the evaporator if you aren't very careful. I have done it on 4 DeLoreans to date and can vouch that it is a bitch especially on the early style with the pipe exiting the bottom. I can't say much about R-413, but if your system was just converted from R-12 without replacing the accumulator -- I think this would be bad practice. Let us know what you find. Walt ----- Original Message ----- From: "Martin Gutkowski" <webmaster@xxxxxxxxxxxxxx> > Hi All > > I've read the article on DMCnews here > > http://www.dmcnews.com/Techsection/aircondfancycle.html > > And I've recently had my AC re-gassed with a drop-in R12 replacement, > R413 (no this is not a typo). The correct amount of gas is present in > the system, but the compressor still cycles for 3sec at most at 3000rpm. > My AC guy reckoned this was perfectly okay - his pressure guage showed > the pressure falling and rising at what he said was a healthy interval. > > When he gassed the system, the compressor engaged for steadily longer > intervals, but he had put the correct amount in and didn't want to put > any more in. The blowers are freezing. Perhaps I need a new accumulator? > > Martin Yahoo! Groups Sponsor ADVERTISEMENT <http://rd.yahoo.com/M=244522.3313099.4604523.1261774/D=egroupweb/S=170512 6215:HM/A=1595056/R=0/*http://ashnin.com/clk/muryutaitakenattogyo?YH=33130 99&yhad=1595056> Click Here! <http://us.adserver.yahoo.com/l?M=244522.3313099.4604523.1261774/D=egroupm ail/S=:HM/A=1595056/rand=779481584> To unsubscribe from this group, send an email to: DMCForum-unsubscribe@xxxxxxxxxxxxxxx Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service <http://docs.yahoo.com/info/terms/> .
<<attachment: winmail.dat>>
Back to the Home of PROJECT VIXEN