From: Wally Plumley [wplumley@bellsouth.net] Sent: Thursday, July 12, 2001 9:40 AM To: 928 Subject: [928] Re: A/C seal replacement kit? At 06:38 PM 7/11/01, you wrote: >my A/C is blowing warm only 6 months after it being recharged. everything >seems to be working ok, but i think the freon may have escaped. does someone >know of a kit with all the seals that are needed? or any other suggestions >as to what might be the problem? thanks to all. I would suggest doing some testing before any action. 1) With the engine running, A/C on, look at the compressor and see if the center of the compressor clutch is turning. 2) If it is turning, feel of the A/C return line at the firewall and see if it is cold. If it is, the refrigerant system is OK. 3) If it is not turning, kneel down and look in thru the grille at the receiver/dryer (round can between the bumper and the radiator), and find the electrical switch on the side of the can. 4) Pull the harness off, and jumper between the connectors on the harness. 5) If the compressor clutch is now turning, the freon is probably low. 6) If the clutch still isn't turning, you probably have an electrical problem in the compressor circuit. Could be the relay in the control head, the anti-freeze switch, the wire, or the clutch. Wally Plumley 928 Specialists From: Dr. Bob [mailto:dr.bobf@worldnet.att.net] Sent: Monday, August 19, 2002 2:30 PM To: 928 Subject: [928] re: R134a conversion; Pros & Cons? J.P. wrote to the list: >> Greg K., you can probably weigh in on this... >> >> '91 GT w/39k: >> >> My original AC (non converted) has been >> working fine, up until Friday when it didn't >> come on at all. I don't think that I have any >> component problems aside from a refrig. >> leak somewhere. My gut says that I could >> probably add a pound or so of r12 & be >> fine for a couple of years, but that's probably >> wishful thinking. Testing for no freon: Start off with a diagnosis that's a little more precise than based on a gut feel. While the gut is often right, there are sometimes more precise methods. First and easiest step is to find out if you are in fact low on freon. You can locate somebody with a set of gauges to attach to the car. Alternatively you can test or jumper, temporarily, the pressure switch that protects the system from no-freon operation. The pressure switch is located on the tubing manifold that's part of the receiver/drier assembly at the front right corner of the car, in front of the radiator and the AC condenser. On your car, there are two sensors there. One has nuts on it where the wires attach, and the other has spade terminals. You want the one with spade terminals. If you have a continuity tester, pull the plug off the switch, and test for continuity between the switch terminals. If the switch has no continuity, go to the No Freon paragraph below. Switch continuity means that there is freon in there, so you should look at Control Problems below. No tester? Make a wire jumper that will plug in to the wire harness connector. Start the car, turn on the AC switch, and look to see if the belt from the crankshaft is turning the center of the pulley on the AC compressor. If the pulley is now turning, shut the engine off, remove the jumper, restore the connector to the switch, and go to the No Freon paragraph below. If the compressor still doesn't run with the jumper installed, means that the problem is not related to freon in there, so you should look at Control Problems below. Control Problems: The electrical circuit for the compressor starts out at circuit X, the circuit that has power when the engine is running. I don't have your fuse chart handy, so I have to trust you to find the fuse for the AC that feeds from that bus. The same fuse feeds the dash controller and the light behind the AC pushbutton, so if the light comes on you can proceed without worrying about the fuses. The button actuates a relay in the dash controller, a relay that's a known weak spot. From the relay, current flows through a temp switch under the cowl between the wiper arms, through a harness that passes through a connector at the right top corner of the radiator sheet, through the pressure switch that you tested above, and to the compressor clutch coil, the one that actually causes the compressor to spin with the belt. There's a separate diagnostic procedure for that compressor control circuit, which I can send on request. It includes a detailed procedure for diagnosing the problem, and an example of a fix I used on my car. The procedure is also archived at the Greg Nichols tip site, by the way. >> >> When I called around to various shops & AC >> specialists about getting an r12 charge, >> everybody recommended against it. Some, >> because they don't deal with r12 anymore >> because of its cost and availability; but others >> that do have r12 say that since I have a leak, >> in order to troubleshoot & fix it, it would need >> to be evacuated... No Freon: There are various ways to find the leak. Best is an electronic sniffer that detects very minute quantities of freon, leaks that measure in the grams-per-year range. More popular is the UV dye method, where a dye is injected into the system, and a blacklight is used to find traces of the dye that have leaked out with your oil. Without knowing the history of your car, you may in fact have a grams-per-year leak, and the best method might truly be a pound or two of R12. You know that sometime in the future you'll be in there again, so it's a decision based on conversion cost vs. a freon cost. >> & I might as well do the >> conversion since I'm where I am. I guess the >> pros are cost of r134 over r12, and eventually >> complete obsolescence of r12. It will be a while before R12 is completely obsolete. Following the Montreal Accord, manufacturers had a couple years to stockpile R12 before the manufacturing ban actually took effect. The ban is hardly universal, with many major manufacturers carrying on the production in most parts of the world. Western European countries, Canada, the US, Japan, and a few others respect the ban. Many other countries, like Mexico for instance, are not bound by the ban and continue to source R-12. Dupont has a major operation in Mexico that still pumps out R-12. The cost issue is another factor though, as a progressive tax makes future purchase of stockpiled US R-12 more expensive as time marches on. >> Are there cons >> to an r134 conversion? Assuming that my >> components/hoses are fine, and the leak will be >> detected & repaired, what's needed for the >> conversion aside from adapter 'valves' >> receiver/dryer, oil and freon? Unless your components/hoses have been replaced in the last five years or so, you can't assume that they are good enough for R-134a service. There are varying opinions on the suitability of oil-soaked R-12 hoses, and mine is that they should be replaced. Along the way, no matter what the hose decision, you'll definitely need to install new o-rings at every connection. Since the hoses will all be loose for this part, why not replace with known good hose? The expansion valve has a temp profile that optimized for the gas that's in use. R-134a has a slightly different temp/pressure profile at freezing, and a bigger one at around 100f. The difference at freezing is the one you can take care of with a new expansion valve. You can gain up to about eight degrees of evaporator temp advantage with a correctly tuned expansion valve swap, assuming that all the rest of the system is intact. Got rear AC? Get the right valve for the rear too. Both are easy to change while all those lines are apart for the o-ring upgrade. So the list is: Hoses, o-rings, expansion valves, oil, gas, drier, conversion valves, a label for the radiator. >> Are there any >> good conversion kits out there for these cars? Yes. Charlie Griffiths packages some kits that include the parts listed above. You can get them directly from www.griffiths.com, but some of the Big Three have mentioned that they are available for bit less through them. Talk to your favorite among them for the details. One of the favorite vendors supplied all my components, excepting the hoses, from stock, and at a very favorable price. I had my hose assemblies rebuilt locally, using barrier hose to replace the rubber sections, also at a pretty good price. Charlie (and therefore the Big Three) also offers some interesting rotary compressor options if you are having compressor problems at the same time. From your description of the low miles on your car, that probably won't apply to you though. After that, it's up to the guys doing the conversion to get all the joints sealed well, get the old oil cleared out of the compressor, and get the system evacuated thoroughly and charged correctly. >> Is it true that R-134a is not as efficient as r12? R-134a is, for our purposes, just as 'efficient' as R-12, assuming that your components are up to the task. The biggest concern with R-134a conversions is the higher heat load and subsequent higher condenser pressures that go along with it. This is solely a function of boiling point and the pressure/temperature curves for R-134a flash. Fortunately, the 928 has a relatively large condenser area, no doubt the result of all the problems seen in the 911-series cars in the earlier years. Since the 928 was a clean-sheet design, it wasn't too big a problem to get a bunch of condenser capacity designed in from the first day. Later cars, '87+, have dual-pressure-switch function in the system, protecting the components from possible overpressure problems should the fans fail or perhaps you find yourself in 120f+ traffic, idling for extended periods. Part of that high-pressure problem also stems from folks overcharging with R-134a. R-12 is a heavier gas, that is it has a higher molecular weight, than R-134a. To get the correct -volume- of R-134a, you need to undercharge your system by 10% or so, based on weight of the charge. This may be where the myth of "less efficient" comes from, thinking perhaps that the compressor is a positive-displacement pump that isn't sensitive to gas pressures for most efficient operation. I hope this answers all your questions. Wally Plumley has put together a pretty good primer on 928 AC function, I hear. Might be worth begging a copy of that from him to help back up your understanding of the AC system in the 928. Nothing like lots of knowledge when you make a decision like this. FWIW: I converted my '89 S4 a few years ago, and was getting subfreezing vent temps from it after the conversion. Needless to say, I'm a fan of the conversion process. I also spent the best part of a day doing the work myself, and another hour the next day putting the gas in and cleaning everything up. This is not a trivial task whether you choose to do the work, even part of it, yourself. There's a $$ factor when you hire out the work, plus I wonder if every seal has been replaced correctly, etc. If anybody shortcuts anything or doesn't get it just right, you will be back in there just after your 30 day warranty expires, trying to find the two black o-rings inadvertently left in the system someplace. Of course, that fix will again cost you an evacuation and recharge after you remedy the problem. For me, this o-rings were the ones where the hose fitting attaches to the compressor body. Happens to the best of us, but can be expensive and frustrating.