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Old 07-24-2014, 10:29 AM   #1
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Default Blower speed and AC switch input

This past weekend my brother re-configured my MS2 so I can get better idle when AC kicks ok. The MS looks at 1Q grounding (AC clutch energized) then bumps up idle 300rpm and after short delay allows the 1J output to energize the AC clutch relay. It works great! Much better idle with AC on now!

Here is the problem, it only works with the blower switch in position 1. If I move it to 2,3 or 4 it will not keep the clutch on. Every now and again you can see the clutch try to engage and the fans bump. The MS shows the AC input coming in briefly and then going away.

If I take the blower switch back to 1 it works great! I have looked at 3 different wiring diagrams for my 91 and cannot see anything that would show the circuit that grounds 1Q changing with fan speeds. Am I missing something here?

Could I just have a bad blower switch? It doesn't make sense because it controls the 4 blower speeds just fine.

I am about to go back to jumpering 1Q and 1J, and wire an input off of the AC clutch circuit to let the MS know that the clutch is on. I will not be able to delay the compressor start after bumping up the idle, but I will at least still be able to increase idle duty cycle when AC is on. I tested it in blower speed 1 with no delay and it is still enough to prevent a stall when I come to a stop. I will then wire in a N/C relay contact in the AC coil control circuit to work as a high RPM or TPS based AC cutout.

Does anyone know why I would see the AC input on 1Q in blower speed 1, but not in the other three speeds?
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Old 07-24-2014, 10:43 AM   #2
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I don't have the wiring diagram in front of me. However, if the switch has one contact set that selects fan speed and a separate, wiping symbol that is in series with the A/C switch, then that wiper-looking contact set is bad. I'm thinking that is very likely.
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Old 07-24-2014, 11:06 AM   #3
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what exactly did your brother do?
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Old 07-24-2014, 12:44 PM   #4
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Miata Specific research:
https://www.miataturbo.net/megasquir...-verify-67046/

Hardware Mods:

AC input circuit:
1Q -> Active Low Input Circuit > DIP40pin10 > JP4 > PEO
http://www.msextra.com/doc/ms1extra/...s/lowinput.jpg

AC output circuit:
1J -> Relay Control Circuit (1K, TIP120, IN4001) -> AD6

Firmware = ms2extra_3.3.2

Software Configuration:

Startup/Idle > Air Conditioning Idle-up
A/C Idle-up=ON
Idle-up Output=AD06/JS5
Idle-up Input=PE0/JS7
Idle-up Input Polarity=Low
Idle-up Delay(ms)=0
Idle-up Min RPM=0
Compressor Delay Since Last On(s)=0
Idle-up Duty Adder(%)=17.4

MS Testing:
Tested mods on Stim: Output grounds when Input goes low

Car/Wiring testing:
Confirmed that grounding 1J causes AC compressor clutch to engage
Confirmed that 1Q is going to ground when AC sw is on and Fan on 1

Observations:
Intermittent grounding behavior on 1Q when AC sw is on and Fan on 2.3.4. This is odd as blower, AC, and fans work correctly when 1Q and 1J is jumpered?

Proposed next steps:
I need to verify the expected behavior on 1Q so I can confirm or deny the possible wiper issue on fan switch dial.

Follow up Questions:
Can somebody point me to a (confirmed) diagram or description of what we are supposed to be seeing on 1Q on a 91?

Thanks,
Servaas (Relte's Brother)
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Old 07-24-2014, 12:57 PM   #5
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What he said^^^^! Sorry, i just know enough to get in trouble.
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Old 07-24-2014, 01:07 PM   #6
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I'd look at the input circuit built.

I'm guessing that circuit is keeping the voltage higher, enough where it's above the MS's low trigger point and the MS is not triggering the output.

if you actually measure the voltage at 1Q, youll see it's very low when on fan speed 1, and rises slightly as you go up to fan speed 4.

take a reading on 1Q on the different fan speeds and report back. IIRC the voltage needs to drop below ~1.7v before the MS will consider it "triggered"

im also guessing, that if you ground 1Q by hand when the fan speed is at 4, it will work. (you can introduce the ground at the thermoswitch plug).


I think you need a 12v pull-up, 1Q might stay at 12v normally when off, i cant remember, you can test.

I suggest building the circuit that MS3X expander uses for teh tableswitch input: http://msextra.com/doc/general/ms3v3schems.html#ms3x
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Old 07-24-2014, 02:17 PM   #7
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My further thought is that if all 4 speeds worked before, it is doubtful it just went bad. More likely a wiring error.
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Old 07-28-2014, 08:53 PM   #8
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The voltages measured were 4.6V with fan off, 0.9V speed 1, 1.4V on 2, 1.6V on 3 and 1.7V on 4.
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Old 07-29-2014, 09:07 AM   #9
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voltages are in line with what I measured last time. I was having a similar issue in my car, but that was after something randomly odd happened in it where EVERYTHING was screwed up. Never could quite figure out what the cause was. But I eventually switched my input on the mainboard (using that active-low) to bringing it in on the expander board and that at least solved that.
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Old 07-29-2014, 06:03 PM   #10
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Great,Those voltages explain the observed behavior.

I am first going to try changing the pull-up resistor on the existing circuit. With a higher ohm resistor it should keep voltage below the threshold on all the fan speeds.

Servaas
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