Bill Ball

Hi Guys:

I am doing another AC controller relay replacement, this time on a 90 S4. The relay on the 90 S4 controller board is completely different from the Gruner 202 I am used to seeing. I haven't done anything newer than 89 before. The 90 S4 relay is a Matsu****a DSP2a-DC12V-R and the layout is different. Also, the board traces are different. It has me really confused about which pins to match on the RS 275-218. Take a look at this:



Pins 2 and 3 (circled) on the Gruner are unused. The Matsu****a has only 6 pins but the middle pins on each side go to a wide solder pad that includes the original pins 2&3 and another wide pad that includes pins 2&6 through a new hole drilled between each pair (so there are now 10 holes instead of 8). Pins 2&3, unused with the Gruner, now go to one of the edge connector fingers. [Note: the Matsu****a actually uses a different pin numbering system; I changed it above to coincide with the 1-8 Gruner pins.]

Bill Sanders did a write-up of changing the relay in his 94 GTS. It has a very similar Matsu****a relay, although the polarity on pins 1 and 5 are reversed. The weird thing is he hooked up the Radio Shack 275-218 exactly as we hook it up to the Gruner!

Here is the RS 275-218 arrangement.


Here is the match-up Gruner to RS 275-218


Any suggestions for the the Matsu****a-RS match-up? Bill used the same match-up as with the Gruner. I can do a timing belt in my sleep, but 928 electrics continue to stump me.

IcemanG17

odd............even more odd since I can't read electrical diagrams at all...... I'm lucky to figure out how to use my Fluke tester, just to get an ohm reading....... We should start an "electrically challenged 928 owners support group!"

Rob Edwards

EDIT- Oops, reading comprehension. I wrote this all then noticed you're talking about a different relay. Weird, my car is a midyear build #278, birthday 1/10/90, and had the old Gruner relay in the head. Ah well, I'll leave the pics up.......

Bill-

I used a 275-218 on my '90 GT head, here are some pics that I hope illustrate how I did it. I used three different colors of wire so hopefully you can trace where each one goes. I used Bob's directions and it works just fine. Just don't ask me how it actually works, 'cause I have no freakin' idea...

First, the old relay:



Then the wiring on the board:



And then the wiring on the relay:



Closeup of the relay wiring, brightened so you can see it:



Yell if this doesn't make sense or isn't clear enough.


Alan, please don't look too closely at my soldering skillz. Yes, I should have used bigger diameter shrink wrap that might actually have fit over the terminals....... Duh!

Bill Ball

Rob: I understand (or at least think I do) the Gruner relay and how to substitute the RS 275-218. It's the Matsu****a relay I encountered in the 90 S4 that threw me for a loop.

Bill Ball

Here's the way the Matsu****a-RS match-up looks to me.



But the fact that Bill Sanders successfuly used the Gruner-RS match-up posted previously has stopped me from proceding.

Bill Ball

OK. I'm definitely running for President.

ROG100

Bill,
Doc Mirror is your man and he is a genious when it comes to this stuff just like Alan.
I will PM him and see if he can chime in.
Roger

Bill Ball

Bill Sanders reported back that his AC is working fine using the Gruner to RS 275-218 mapping even though his 94 GTS has a Matsu****a relay. I'm baffled, which is par for the course with me and 928 electricals. I hope Doc or Alan, dr. bob, borland or any of the other electrical gurus take pity on me and help me out of my predicament.

Alan

Bill - your final mapping looks good to me. Without looking at yours I worked out the same thing except I had 5 ->7 & 1 ->8 (yours is 5 ->8 & 1 ->7) which just reverses the coil connection (which doesn't matter) but I did it that way to maintained the same pin between the Gruner & Matsu****a. Either way is fine. Is its possible Bill had a different pinout on the relay he replace/used?? otherwise I don't understand it...

BTW I have used a quite different preventative approach to this that I've never mentioned. Before my relay showed any symptoms of failure I added an additional relay on the CE panel to drive the AC clutch. This is just a standard SPST relay and is of course easily replaceable. The Clutch signal already goes through the CE panel so this is fairly easy to do. implementation varies slightly by year.

Alan

Bill Ball

Alan:

I wasn't sure of the polarity of the Gruner pins for the coil or the RS relay, so I just picked either. Glad to hear it doesn't matter. The Matsu****a relay in the 90 has the coil polarity reversed from the 94 GTS relay and most other DSP2a relays; hence the -R, I would suspect.

Here is are top and bottom picture of the Gruner and 90 S4 relays. The bottom view is from flipping horizontallly (<----->). The Gruner relay is symetric so the order right to left is not relevant, but the Mats is not symetric. I think I got the order right when I converted the Mats pin numbers to 1-8 in my first post. Maybe you can check my work again.



Although there has been mention of saving the controller relay by having it trigger another relay instead of directly driving the clutch, I wasn't sure where to mount and wire that, but you've just provided that information.

THANKS! YOUR ASSISTANCE IS INVALUABLE!

I will report back after I wire the relay. I still don't understand how Bill Sander's is working.

docmirror

Sorry, under a hot airplane all day. I don't see the cooresponding numbers on the Mas relay, so here's the xover by Mats pin and RS pin:

RS........ Func..........Mats......photo loc as seen from bottom with edge conn on left:
7..........Coil pick..........1..........Upper right
8..........Coil pick.........16.........Lower right
5..........Wiper.............5..........Upper ctr
6..........Wiper.............12........Lower ctr
3.........Norm open........8........Upper left
4.........Norm open........9.........lower left

Note that when you poke the wires in from the top you will be soldering from the bottom. Orient the head so that the edge connector is on your left hand, and the ***** face away from you. The coil pick lines will be on your RIGHT. The wipers will be in the CENTER, and the Norm Open contacts will on the LEFT. So, two wires on the right(solder side) go to 7 & 8 on the RS, Middle wires go to 5 & 6 on the RS, and left most wires go to 3 & 4 on the RS.

Or, send the whole thing to me, and you'll have it back in a few days all setup. Roger will also exchange for a good one that has been done and tested.

Call if you get stuck.

Bill Ball

Thanks, Doc. Yeah, I renumbered the Mats relay pins. Maybe more confusing to do that. . I'll look over you match-up and get soldering later tonight. I already did the wires to the board awaiting the proper relay pins to match up. Gotcha on the bottomside re-orientation. And thanks for offering to do this for me, although I think this is just within my skill level with electical stuff.

Bill Ball

So, to better illustrate Doc's match-up for electrically challenged like me, here are the relevant diagrams.



I had it right, as Alan said, but just keeping the Matsu****a numbering on the relay makes it clearer.

Thanks to Alan and Doc.

The pin match ups are different for MY89 and before controllers based on the Gruner relay. The 94 GTS has a Matsu****a relay with the polarity of 1 and 16 reversed, but otherwise the same and can be wired as shown here.

Bill Ball

OK, the 90 S4 AC controller now signals the compressor clutch with the above relay wiring. Now I just have to get the temp control working, as the car only has AC when the temp is set all the way down (tripping a microswitch). This should mean the inside and/or outside temp sensors is/are bad. I hope it's the outside one - I have spare and it is far easier to replace than the inside one. ONWARD! Thanks again to Alan and Doc.

Bill Ball

Well, fortunately the temperture regulation was relatively easy to fix. After I located the harness plugs in the center console, the inside sensor tested good, the outside bad. The external plug in the wheel well to the outside sensor was heavily corroded inside, but that wasn't the only problem. The sensor itself was bad. With a new (used) sensor, and competely reworked plug, the AC is entirely fixed now. It needed a new clutch (the coil was shot), controller relay and outside sensor and plug. I'm happy again. The diagnostic and repair time and parts would have probably been over $2K at a shop.