CQ AC relay or early hitachi ECU question

[ShadowofBob]

So I charged my AC on my CQ which has retrofitted B4 Climate control. And it does work...sort of. The control head says all is well and that the AC is on. The trigger wire from the head is being grounded when I turn the AC on. Unfortunately my AC relay doesn't appear to be working. Does anyone have or know the pinouts on it?

I know:

87: To AC clutch(is bridged with 30 upon trigger)
30: +
5/T: + trigger wire(+ w/ ignition)
31: ground (is controlled by HVAC head)
87a: ???

Does anyone know what 87a is? It goes to pin 24a(this is also bridged to 8a) on the early Hitachi ECU. I think it is just a signal(12v w/ ac clutch engauged, 0 w/ it not) wire for the Hitachi ECU but I am not positive on that. Does it need to be connected for the relay to work? I had it bypassed since the B4CC can do this function with one of it's own outputs. I tried reconnecting and it didn't do anything.

I'm think my relay coincidentally failed since working 6 months ago or I somehow burnt it out. Although I am not sure how since all looks good, unless the 87a does more than I thought.

[panzerwagen]

I'd say you may have to score the Bentley Manual ....

just for the electrical schematics. It is worth it's cost just for the electrical info it has.

[S2central.net]

I like a challenge

[S2central.net]

87: To AC clutch(is bridged with 30 upon trigger) : YES

30: + : YES, routed from pin 19 on head-unit actually

5/T: + trigger wire(+ w/ ignition) : This one is confusing. Bentley has a typo showing bk/gy connection to a/c programmer on track 35 which is shown on another page as bl/gy. This would seem to be pin #5 on the controller.

31: ground (is controlled by HVAC head)

87a: This is just described as connecting to fuel injection control unit - must be signalling one way or the other. Further investigation required. I can scan this if you wannit

[S2central.net]

Right - found it...

That pin 4/87a should track to pin 24A on the ECU of the 7A engine (MPI) this is a 0.5mm wire that is also bridged to pin 8A on the MPI ECU.

Note also that pin 23 on the head-unit should connect to MPI ECU on pin 12A - this seems to be a black/yellow wire.

HTH - Just shout if you need the schematics, or more help if this for a different engine application

Paul

[S2central.net]

WARNING - DANGER - that info above only applies to MPI ECU up to 8B-L-001109 (approx March 1990).

Later ones have DIFFERENT MPI wiring which I've just noticed such that

A/C Relay pin 87a goes to MPI pin 10C
Head Unit pin 23 goes to MPI pin 11C

To clear this up let me know which drawins you need

[S2central.net]

This shows it pretty well - for a 3B application of the old clima system in a Coupe --->

http://www.s2central.net/S2_Schematics/D/D45.PDF

[S2central.net]

And this one for sweeter digital climate control as per B4. This for ABY, but you'll see the important differences and signalling links to ECU which you can extrapolate to 3B or 7A

http://www.s2central.net/S2_Schematics/B/B75.PDF

[S2central.net]

Looks to me like pinout on the relay at position 4 is different between old clima and new system.

[ShadowofBob]

I do have the Bentley manual. It doesn't go into enough detail on the functions of each pin on the ECU for my liking.

Thanks for the info. The reason my wiring is different is because of my B4 climate unit I swapped in. I bridged 5/T with the other positive signal wire on the ac programmer so that it is + all the time since the B4 unit grounds rather than turns the + signals on.

I guess I'll just leave the relay hooked up to the ECU and not the B4's signal wire, at least until I do more testing and confirm it functions the same way as the B4 wire.

Unfortunately something has gone awry in my my B4 head. Now my wire that triggers the clutch relay isn't grounding for some reason. It does still go from infinite resistance to 230 ohm with the AC on, but doesn't pass my multimeter's continuity test with a ground. Either something inside is bad or my wiring is at fault.

If I can't fix it would it be a bad idea to use the unused signal wire(12v w/ AC on) that goes to the motronic ECU to trigger the relay?

No codes are being thrown from the climate head(well asides from my interior temp sensor fan being faulty, but that is insignificant) and it thinks it is triggering the AC on.

[S2central.net]

Just get the right flavour of Relay #4 installe and check the wiring up to its pins from your new loom is correct.. That should get you going.

Paul

[ShadowofBob]

I have the correct OEM relay(got an extra couple at the junkyard) that came with my car. The problem now is the trigger wire issue I mentioned in my previous post.