een chasing through diagrams all morning and cant figure it out.
Car is a 99 thats been pretty thoroughly hacked up. Harness and all (its an engine swap race car being put back on the street)
Anyway, i need to control the hvac setup. All i need is a signal from the a/c button on the dash to trigger my relays and such. Power or ground, dont care.
I cannot figure it out for the life of me! What wire is the ac button output, and is it power or ground?
The AC relay is triggered by a ground signal from the ECU. On a 93 it is blue/black.
If the Miata ECU is not being used, I would guess that the signal from the switch that goes to the ECU would need to be hijacked. Once again for a 93 it would be a green black. Best place to find and conect there two would be at the Miata ECU plug.
I believe that for later cars there is a second splice needed but I dont have the diagram for the later cars.
This is the wiring diagram I've been using for my 99s: 1999 Miata wiring diagram
The headings are a little misleading, but the A/C system is on page 3.
A/C switch shows pink wire (12V in), black/blue wire to A/C amplifier, blue/yellow to fan circuit.
Not sure what the outputs are without putting a meter on them, but I would guess black/blue is the one you want.
I just realized i never want to swap my car to a Chebby v6
In reply to Rodan :
Same exact duagram im using. What/where is the ac amplifier?
In reply to Dusterbd13-michael :
Upper left corner of diagram. Diagram says "Behind right side of dash". I've never messed with it myself, so I can't say exactly, but I'd look in the area above/behind the glovebox. It connects to the refrigerant pressure switch and evap temp sensor, not sure of its exact function.
Had to go look this up:
If your air conditioning system has a heart, it would be the compressor. It keeps the flow of the whole system in motion by compressing and transferring the refrigerant gases. But for before it starts doing what it does, another component is needed to take control of the compressor. And that's exactly what an A/C Amplifier does. If the compressor is the heart, this device is the brain that handles its overall function. It serves as a control module which directs the operation of the compressor based on various inputs like evaporator temperature, low-pressure switch, and A/C request. Aside from this function, this component also acts as a protection device. It's able to do this by comparing the speeds of both the engine and compressor. By determining whether the speed of the two devices match, the amplifier is able to prevent the compressor from incurring any damage by turning it off when its speed is not in sync with the speed of the engine. Due to its important role, it's important for this device to have a long service life
Not specific to Miata, but to expand on the above:
The chassis manual has a nice section on the AC system, even diagrams the circuit for you. the "magic blue knob" does exactly as mentioned, adjusts when the amp will let the clutch engage in regards to RPMs.
Clockwise=lower RPM
CCW=higher rpm required to run the AC.
The amp gets a signal from the coil, same wire as the tach, that it reads for RPM.
Thermister and pressure switch functions are also controlled in the AMP, it all come down to telling the compressor when to run and when to shut off.
Just remember that to bypass the entire amp just jump the yellow wire to the black with white wire and the clutch will engage when the AC button is pushed, disengage when the button is out.
Justjim75 said:I just realized i never want to swap my car to a Chebby v6
Chevy makes it easy. The computer controls the compressor clutch and the fans and does the idle-up strategy, all you need to tell it is if you want the compressor on or not. Which you can do by just splicing to the chassis' compressor-on wire. Might have to use a relay to turn a power into a ground, it's been a while.
In reply to Knurled. :
My patience and personality, combined with my lack of facilities or patience, lead me to think my lack of patience for things like harness splicing and nonexistent patience would end in fire
A GM powered Miata is honestly more fun than most one night stands I've had. However it requires more patience and attention to detail than saving my marriage ever did. And I still can't figure out the damn AC signal to fire a relay to fire the compressor with the factory button
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