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Old 05-13-2013, 07:21 PM   #1 (permalink)
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Default P28/AC function (A15, B5 etc)

how does the ac system work in relation to the p28 ecu?

Does the p28 bump idle to compensate for the load? Or do the engine sensors otherwise compensate for the additional load?

Im specifically wondering what roles B5 and A15 play in the ac system. Are there any other pins in the PCM that relate to AC?

Are they output functions or inputs? All I can find is, for example, A15 = clutch.

This doesn't tell me much.

Is this an output function that turns ON the clutch? Or is it an input FROM the clutch that activates something else in the P28?

Looking for as much info regarding the p28 and is overall scope on AC function. Bore me with details!

Thanks guys.
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Old 05-13-2013, 07:50 PM   #2 (permalink)
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B5 = AC Switch - Input to ECU.
A15 = AC Clutch - Output from ECU to AC clutch relay.

the P28 does have a routine to adjust IACV duty cycle when the AC is turned on. in addition, it has a recovery point below which RPM the AC is disengaged to prevent the engine from stalling. there is also a routine that disengages the AC clutch above a specified TPS / load.
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Old 05-13-2013, 08:09 PM   #3 (permalink)
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Thanks for the reply!

When you say ac switch do you mean a pressure switch or do you mean literally the "on" or "off" switch on the dashboard that's labeled "ac"?

What is the voltage reference for B5? Or is it a ground input?

let me just get to the point.

I'm finally reinstalling my ac in my d16z6 swapped 83 civic.

I'm running the d16z6 with an OBD1 engine harness/chipped P28 (deleted ELD etc) wired as a standalone/piggy backed on top of the 83 chassis harness.

The 83 civic ac system is completely self contained in the 83 harness as far as wiring goes.

The only "output" wire I have from the 83 civic ac system is the wire that would have originally gone to an ac idle boost solenoid. It's actuated as a 12v output from the 83 ac clutch relay. I saved this circuit just in car I ever needed it.

I'm curious what the best (simplest) way to reinstall the original ac system would be.

Thinking about just hooking the lines up, recharging, and letting it rip since the 83 ac system is self contained in the untouched 83 chassis harness. In other words, I wouldn't need the p28 to turn anything "on" or "off" for the ac system to work.

does the p28 NEED to see that the ac system is on? based on what you said it seems like the p28 is pretty involved in running the motor correctly while the ac switches on or off - not sure how to integrate the 83 ac to the p28. so I'm at a loss.

What are your thoughts on my idea? I get the sense that I'm over complicating this but I'm really not very familiar with OBD1 honda electronics

could i cut the wire from the ac switch (cut between switch and relay) and feed the switch to b5, then send A15 back to the relay?

Last edited by Jonathan_ed3; 05-13-2013 at 08:16 PM.
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Old 05-13-2013, 08:24 PM   #4 (permalink)
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Quote:
Originally Posted by Jonathan_ed3 View Post
When you say ac switch do you mean a pressure switch or do you mean literally the "on" or "off" switch on the dashboard that's labeled "ac"?
the button on the dashboard. actually, it is a combination of the button, the blower knob and the AC pressure switch. if either one of these is open, B5 will read open.


Quote:
Originally Posted by Jonathan_ed3 View Post
What is the voltage reference for B5? Or is it a ground input?
ground input, like all other switches in the system.


Quote:
Originally Posted by Jonathan_ed3 View Post
The only "output" wire I have from the 83 civic ac system is the wire that would have originally gone to an ac idle boost solenoid. It's actuated as a 12v output from the 83 ac clutch relay. I saved this circuit just in car I ever needed it.
that circuit will not be used with an OBD1 system.


Quote:
Originally Posted by Jonathan_ed3 View Post
Thinking about just hooking the lines up, rech, arging, and letting it rip since the 83 ac system is self contained in the untouched 83 chassis harness. In other words, I wouldn't need the p28 to turn anything "on" or "off" for the ac system to work.

does the p28 NEED to see that the ac system is on? based on what you said it seems like the p28 is pretty involved in running the motor correctly while the ac switches on or off - not sure how to integrate the 83 ac to the p28.
the ECU is integral to the AC system. you can always bypass it, but it would be highly unwise to do so. you *need* to route everything to the ECU to get your engine to idle right, disengage AC on high load, etc.


Quote:
Originally Posted by Jonathan_ed3 View Post
What are your thoughts on my idea? I get the sense that I'm over complicating this but I'm really not very familiar with OBD1 honda electronics
based on what you're saying, I would assume that you are familiar with electrical wiring in general. I would suggest you download a D16Z6 factory service manual, look up the wiring schematics and wire your system accordingly.

at a high level, it's simple. feed the AC switch input to B5 and feed the A15 output to the AC clutch relay and condenser fan relay.
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Old 05-13-2013, 08:29 PM   #5 (permalink)
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Thanks! I'll try that out tomorrow!
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Old 05-14-2013, 06:31 AM   #6 (permalink)
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https://www.d-series.org/forums/gener...g-diagram.html
Second diagram has it
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