From: rkertesz@home.com [mailto:rkertesz@home.com] Sent: Friday, July 06, 2001 3:12 PM To: 928 Subject: [928] A/C switch wiring Okay, here's one for all you 928 wiring gurus (I knew I should have bought that set of shop manuals when I had the chance). The A/C switch on the center console has gotten to be flakey (it's in an '88 S4 btw). It turns on the compressor about 20% of the time. Sometimes pushing the switch on and off five or six times gets it to work. I would like to get in there and wire in a standard on/off push button switch. My question is this: There are four connections comming off the switch. What do they all do and do I need them all connected to get the A/C to turn on? Thanks in advance for any help. Ron 88 S4AT Satin Schwarz Metallic From: David Schmidt [david.schmidt@ind.alcatel.com] Sent: Friday, July 06, 2001 6:37 PM To: 928 Subject: [928] RE: A/C switch wiring This is a known problem, and probably NOT the switch itself. The switch powers a relay located in the HVAC control head (behind the temp sliders) and that relay is not spec'd for the AMPs it needs to switch. I had the same symptoms and followed the instructions at http://www.928oc.org/tip/tip055.htm. Now the switch/relay work fine. Be sure to download the PDF file created by Dr. Bob. It has a nice drawing and complete instructions on how to do the job. I just used a Radio Shack 12v relay with a much higher current capacity. Louis Ott lists a couple part numbers on the 928OC tips page. Let me know if you have trouble with the link and I'll forward you the PDF file that Dr. Bob sent me. David Schmidt '90 GT, Guards Red, RMB davids@tower-mt.com http://www.tower-mt.com From: Dr. Bob [mailto:dr.bobf@worldnet.att.net] Sent: Saturday, August 10, 2002 11:37 AM To: 928 Subject: [928] re: AC trouble shoot Tony wrote to the list: >> With AC button pressed the "AC" light >> illuminates. I have LP switch jumpered, >> freeze switch jumpered, both coolling fans >> come on. a good 12V measured at LP >> switch, freeze switch and the connecter >> leading to the compressor on the front of >> the engine. When i cycle the AC swicth the >> voltage changes accordingly...12V...appx >> 0...12v..etc etc >> <> >> >> Question: I have good voltage but my guess >> at this point is not enough amps in the circuit >> to engaged the clutch. What amperage >> would/should i see? >> >> I know quite often the "little blue relay" in the >> control head is the culprit but i have a good >> 12v all the way to the compressor. Could a bad >> little blue relay still cause bad amperge even >> though i have good voltage?? Hi Tony-- Nice to meet with you again at the Devek weekend. I did a write-up on the relay diagnosis, and also the cure I used to fix my '89 when it was suffering from the same problem. I'll send a copy of that to you directly in a separate message. For those reading along at home, the key to deciding whether the relay is the problem is how you do your troubleshooting with the meter. The problem we most often see is a high resistance in the relay contacts. With the compressor clutch coil disconnected, the current in the circuit is alomost nothing, and the resistance causes virtually no drop in voltage on the clutch circuit. Connect the clutch coil and the current requirements go up to maybe six amps, and the voltage drops due to the contact resistance. So the troubleshooting technique should include testing voltage at any of the test points. The freeze switch is easiest to get to with meter leads with wiring still attached, but you can do it at the pressure switch, the sandwich connector by the jump terminal, or at the compressor wire connector too. You already made jumpers for the switches, so either point will be OK. The key is to do it with the load (compressor clutch coil) still attached. The little blue relay in the control head is not rated for six amps, is not rated at all for DC service, and is not protected from inductive field collapse when the clutch coil is disengaged. All these things work together to cause contact arcing whenever the relay is used. This arcing will soon cause the contacts to pit, and the excessive current can cause the arm in the relay to warp from all the heat as the contact resistance grows. After that, it's a death spiral for the relay until it no longer carries enough current to pull in the clutch coil. The 'fix' that I came up with involves removal of the original underspec'd relay, replaced by a larger more capable relay that's commonly available. Unfortunately, I was not able to locate a little flat-pack power relay as a direct replacement, so I wired a larger relay outside the controller case and attached it to the case with double-stick tape. After four years it's still hanging on there, so the mechanical portion of the install is fine. The electrical function has also been flawless. If you decide to go this route, the relay and the connecting wires are common Radio Shack parts. You'll need a soldering iron and rosin solder for the wiring, wire cutters, etc. To remove the controller, you'll need to remove the center vent, the plastic "H" trim on the console, the radio (needs a coat-hanger tool), and finally a small phillips for the screws on the controller itself. A couple small screwdrivers will get the controller sandwich case apart, and after that it's the electrical repair. The complete repair procedure is described is in the diagram which is available directly from me, and also is archived on the Greg Nichols website in the AC section. I'm on a dial-up connection in the wilds of Illinois right now, so if you can grab it from Greg's site it will make my day a little shorter. ;-) It's important to note that both new and rebuilt controllers come with the same underspec'd relay inside. In my limited experience with such things, it's a matter of "when" rather than "if" the relay will fail. Mine was history after only about 28k miles, albeit soCal miles where the AC was used a lot. Living in Las Vegas, Tony probably only uses the AC once a year, turning it on in April and off in October. It might get a vacation for track days but that's about all. Hope this helps! dr bob From: Wally Plumley [mailto:wplumley@bellsouth.net] Sent: Saturday, May 24, 2003 5:24 PM To: 928 Subject: [928] Re: A/C Control Head - Climate Control Relay At 12:55 AM 5/24/2003, Charles McGuire wrote: >1980 928S - Climate Control 80-83 - short version: Anyone have a good >source / part # for the notorious relay inside it? Maybe a beefier one, >capable of a little more current? Looks like there is more real estate for >a larger part. Dr. Bob? > >Long version: Since I am replacing the notorious shifter ball cup, "while >I am there", I'm replacing the leather shifter boot, etc., and removed the >temperature control / climate control from the console. It has been >"fussy" for several summers. The contacts for the slider switch >(off/eco/auto/<>/Defrost) were dirty and easily cleaned with a pencil >eraser. Likewise the eight "wiper" contacts were brightened with a very >light wipe of fine sandpaper. I'm thinking of using dielectric grease as a >lube for re-assembly, anyone advise against it? The relay contacts >measured 90 Ohms contact resistance. Not good. After a very light touch of >fine sandpaper it now measures 0.3 Ohms on closure. Current required by >this circuit is ___? I'm guessing that cleaning the contacts is only a >temporary fix, similar to filing the points on a model A, not that I've >ever done that... I guess I could measure current draw for the ac clutch, >but the battery is disconnected since there are lots of wires hanging... >One of the optical fibers to one of the slider buttons is broken. Has >anyone successfully polished/spliced these? I'm guessing they are >100-200u? I'm thinking of polishing/sanding both broken ends and using a >piece of shrink tubing to align the ends. > >Charles 80 928S still taking it apart, will I ever get to drive it again?! I can suggest a possible answer for your case. Since you should have a working relay, the goal is to simply keep the system working in a reasonably non-obtrusive, inexpensive manner. What if you bought a simple single-pole single-throw normally-open 12 vdc relay, and mounted it in any convenient location. This relay would be operated by the tiny one in the head unit, so the little relay would see only the small load of the new relay operating coil, while the new heavy-duty relay would operate the compressor clutch. I would suggest mounting it on the passenger fender under the jump start terminal. Hook an in-line fuse holder very close to the jump start terminal for power, run the output of the fuse to the power terminal of the relay, using 12 gage fine-stranded wire. Ground the relay and one side of the operating coil. Run the wire that now operates the compressor clutch to the other side of the operating coil, and run a fine-stranded 12 gage wire from the output terminal of the new relay to the compressor clutch. Reliable power, the little relay should last forever, no permanent mods (except for a couple of small mounting holes), and not very expensive. If I did this (and I have very seriously considered it for the '86), I would add a second 12 gage wire from the output terminal of the new relay to the aux cooling fan. Anytime that the compressor is running, the aux fan would be running. That should improve A/C performance a bit, and help prevent any overheating. Wally Plumley 928 Specialists www.928gt.com