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Mazda Miata NB2 Air Conditioning and Alternator Control

On the NB2 (01-05) Mazda Miata we took some liberties in design to optimize the Air Conditioning(AC) and digital alternator control.

The first half of this will detail how to setup the software in Tunerstudio to utilize AC control as we designed it, the second part will detail how to setup and utilize the alternator control circuit to reduce wear/tear on your alternator and belt system.

For the SpeedyEFI NB2 Plug And Play ECU, AC idle up uses the factory circuits to automatically adjust your engine’s air intake to compensate for added load from the AC compressor, the electrical load from the cooling fan, and your HVAC blower fan.
To utilize this feature on our hardware, you’ll need to use the Programmable Outputs our ECU offers. First, open Tunerstudio, find the Settings dropdown menu, and you will find “Programmable outputs”.
In the programmable outputs menu Rule 1, Output Pin Num 38, Output Polarity Active High, Activation Delay 0, 2nd Condition OR, Condition 1 Coolant Greater than 195(f), Condition 2 Aux in 0 Equal 0, Minimum output time 5.0.
This sets the cooling fan for the AC to turn on when coolant is above 195 degrees, or the AC button is triggered.

Then, change Rule 2, Output Pin 39, Output Polarity Active High, Activation Delay 1.0, 2nd Condition Disabled, Condition 1 Aux In 0 equal 0.
This turns the ac clutch on 1 second after the button is pressed, which gives the engine time to open the idle valve and prepare for the increased engine load of the AC compressor.

Next, we need to set the Idle Up Settings. Idle Up Enabled On, Idle Up Pin 37, Idle Up Pin Polarity Normal, Idle Up Amount 12.
This looks at CPU pin 37 to trigger the idle up based on if the HVAC system is ready for AC.

We also need to set the AUX 0 input to pin D37. 
Open the Accessories menu, at the bottom is the “Local Auxiliary Input Channel Configuration”
Aux0 should be set to Digital_local and Pin No. 37.

For the alternator system, we found that there needed to be a delay in alternator control to reduce belt squeal on startup and excessive heat in the alternator when the key is on, but the engine is not running.

To do this, we added an inhibit circuit which inhibits alternator output when active, and does nothing to inhibit the signal if nothing is programmed.

To enable this feature in the programmable output menus, select rule 3, output pin 52, Rule Alias Alternator Disable, Output Polarity, Active High, Delay 0, 2nd condition disabled, and RPM Smaller/Equal 600.
Then set the maximum output time to 16 seconds.

This sets the ECU up so that when the RPM is less than 600, the alternator will not charge. But it can only disable it for up to 16 seconds, otherwise the alternator works like normal.

8 thoughts on “Mazda Miata NB2 Air Conditioning and Alternator Control

  1. Is there a similar setup for na8 pnp units (purchased after a certain date possibly?) or is hardware modification required?

    1. 94-95 will be different, and 96-00 is its own as well. we should have writeups for both shortly

  2. Hey I ended up with one of the “pre production” 01-05 PNPs. I actually just installed it Monday and am now reading this post. I do not have an option for “Aux 0.” I was wondering if there is an update or something required to fix this. Thanks!

    1. Message us on the FB page if you haven’t already.

  3. When running these settings, my a/c compressor runs all the time. A/C button does control the idle up properly, but the compressor never shuts off. Any edits to suggest?

    1. Shoot us a message on the FB page

    2. Thank you John for pointing out that I glossed over the AUX0 Setup. I have updated the guide.

  4. Just bought your NB Miata Plug and Play don’t know anything about tuning this article on getting the air conditioner working was excellent I sure do appreciate it …now I just got to let auto-tune do its thing and see how far I get thanks again

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