I just moved south 420 miles and damn it's hot and humid. I have been struggling to get my A/C to work and am at a complete loss.

So far I've:
1) Replaced the A/C fan and condensor relay (combined 6 pin relay on a 92)
2) Replaced two o-rings on the A/C compressor which was leaking
3) Tested continuity back to the pressure switch near the passenger headlight
4) Made sure the Fan Relay and Fuse were ok in the main fuse box
5) Tried recharging the system, but the clutch never kicks on

I have upgaded fans which use a relay to power the A/C fan. The relay is triggered by the big fan as it's wired in parallel.

If I use the stock A/C fan wiring to trigger the relay when A/C is activated, it sits just as dead as the clutch on the compressor.

I haven't messed with anything A/C related during my bp4w+ms3x swap and everything was working fine on my 1.6L with MSPNP1.

What would cause both the fan and the clutch not to work? I'd imagine since the ground is separate on the fan, it should run when I jump TFA and Ground on the diagnostic box (with stock wires triggering relay for little fan). But nothing happens.

 

It sounds to me like your not getting a signal. I know MS can be a little goofy sometimes with A/C your sure its configured and you have the settings right? Unless there is an overload tripped (which I'm pretty sure there aren't any on the Miata system) then your failing to call for the compressor to turn on.

 

MSPNP has a pass-through on the daughter board to get the signal from your AC switch to the components. You may need to duplicate this or install a jumper with your MS3X. The MS stickies have a LOT of info on this.

 

Please forgive me as I go full retard....

From Joe's thread:
"Thus, to make A/C work on a '90-'93 with a standalone MS, all you must do is put a jumper between pins 1Q and 1J at the ECU connector. When you press the A/C button, it will provide the closure to turn on the A/C relay, and the rest of the system will take care of itself."


Does this mean literally connecting the two together?

If it's anything internal, I'm electronically inept and may need to ask Brain for help as he built the unit. I didn't think there was more to it since the primary fan kicks on already with the a/c button. I'm lucky I was able to wire the crank position sensor and EBC correctly.

reading this thread has me a bit worried as I didn't assemble the unit myself.

 

Yes, jumper just means to connect the wires together somehow. Can be internal or external to the MS, the electrons will never know. You should ask Brain if that jumper is already there on the MS3X or not (it is on MSPNPs). Then you would know for sure.

 

I just jumper 1j and 1q on the ms harness and it still doesn't engage the aux fan. Going to clean all the terminals again and hope.

 

Your MS3X controls the A/C function. Has it never worked since your install?

TFA + GND doesnt run the A/C fan. There's a diode that prevents the cooling fan relay from activating the A/C relay, but when the A/C relay is activated it activates the cooling fan relay.

The harness is wired so that 1Q goes into the datalog input on the MS3x. When the MS3x sees this input is grounded, it performs its A/C Idle up functions and then grounds the A/C relay on 1J through the INJ H output.

I would make sure that the MS is getting the ground on 1Q and that your condenser thermoswitch isn't failed open or disconnected or something (under dash, behind glove box, towards the center console). Then make sure the software is configured properly to activate the A/C. Then make sure the MS is grounding the INJ H output to 1J.

If that all is good, then it's something between the MS and the A/C relay or the relay itself. Have you tested the A/C fan function and compressor by manually activating the relay?

 

A/C had never functioned since the ms3 install, however, A/C idle up works great which was required early on in the swap as these fans drew so much current the car would lean out and almost stall. So I suppose 1Q is grounding properly.

I never knew about the thermo switch; if its not an electric part, what are the tell tale signs?

I haven't manually tested because after scoping the wiring diagrams I was reluctant to start jumping things here and there.

My electrical knowledge is limited to checking continuity and voltage. That's why I liked mechanical engineering, when it's broken, usually you can see it. :P

I'll try some more stuff today after i get a leakdown test. Thanks for the pro-tips. This is the first time I'm troubleshooting both ac and electrical wizardry.

 

Should I undo what I just did last night (1j connected to 1q)?

 

Leave it connected for now. It's not hurting anything, and it removes the MS as a variable in troubleshooting.

Once you have the system working, then you can remove this jumper. If it stops working at that point, that means something is also wrong with the MS.

 

I'm not free this weekend, but I can take a look at it whenever as well.

 

That'd be great. I'll buy you a beverage or cat of choice.

I'll see what I can do in the mean time with all the suggestions made already.

I can be free most evenings next week.

 

Evenings are fine with me, it's a motivation thing at that point. This sunday might work actually.

can you post your current MSQ in the meantime? make sure it's set up properly.

 

Sure that's fine. I'm around all this week, biding time, before orientation at new employment on Monday.

Attached is the MSQ. I already notice something wrong (unrelated) that I have the injectors set as 900cc instead of 1000cc. hmph.

 

your fan control is set to H not G

and a/c output set to G not H. switch those around.


those outputs dont match the file i sent it off with.


The way it's configured I'm assuming your A/C turns on when the CLT reads over 210°F and the cooling fan turns on when you try to turn on the a/c?

 

Thanks for the catch. I switched fan control output pin to INJ H and A/C idle up output to INJ G.

Still same result. Clutch and aux fan do not kick on.

I wouldn't have known because in either case, the primary fan kicks om when the ac button is depressed.
I'm going to pull some intake bits off and clean the grounds on the compressor. I'll check for voltage tomorrow to see if it's actually getting voltage and just not completing the circuit. Still doesnt explain the fan.

 

The cooling fan relay (in fuse box) gets quite hot during operation. Is this normal?

 

if the main fan turns on when the a/c switch is pushed, assuming we have the outputs correct now, I'd look into replacing the a/c relay. Sounds to me like the MS is sending the ground signal to the relay but the relay isn't switching.

good thing you have plenty of others to swap out in place to test, iirc.

 

The 6 pin A/C relay has been replaced a couple days ago. I tried jumping the pressure switch, and it still has no effect. I'll test voltage but am not sure what values I should be seeing

 

When trying to jump the clutch directly, nothing happens. Either way I think I'm going to have to replace the compressor, on order for tomorrow. I have another A/C relay on hand in case.

I'm losing track of what needs to be done. @_@