A/C button question

[spd]

Quick question regarding A/C... in particular about the way the button functions in the hvac console.


My car has working A/C and it serves the purpose well, but there are two issues with it that keep it from being ideal.

1) the button to engage a/c is a rocker switch on the console

2) there is no RPM window switch to protect the compressor



So I am wondering if the A/C button on the hvac simply connects two pins on the hvac connector together, or if there is more to it than that?

I have seen diagrams suggesting the a/c button is also routed through the fan speed switch, which to me adds a level of complexity that I may not want to deal with.


If, on the other hand, the a/c button simply bridges two pins..  could I simply transfer the wires from my current (console mounted) switch into those two pins? And then be able to use the factory a/c button?



Thanks in advance for any suggestions!

[halfspec]

Assuming you're working with a FD.....Unfortunately the AC switch is more complicated than a switch that open and closes its contacts. Take a look at the Electrical section in the first post of my DIY AC post:

http://www.norotors.com/index.php?topic=12654.0

You'd be concentrating on the right relay in the diagram I posted since it translates the AC switch signal into a more usable format. In your case if you wanted to just remove the rocker switch on your console, you could just build the right side of the diagram and just connect the rocker switch leads to pin 30 and 87 of the relay.
Just be aware there are two versions of the diagram (see the thread above).

A RPM switch is recommended as well. I'm guessing your engine is > LS1 so you're forced to use aftermarket control? If so, you can reference burtoncr's thread for controlling a LS2+ compressor with a RPM switch.

http://www.norotors.com/index.php?topic=846.0

Just make sure you fully understand the diagram. I make kits that do the same job and I don't build them like his diagram shows. I'm not saying it won't work because I've never built a setup exactly like his diagram shows, but I have a sneaking suspicion it won't work for everybody.

Additionally, you can check the AC GB link in my sig and I can set you up with plug and play controller kit for your AC that'll get you setup in a jiffy 

Lane

[spd]

Hey Lane,

If it wasn't obvious, the thread was semi-pointed in your direction lol


I have looked at those diagrams before but I still could not figure out how exactly to wire in the button...  other than it looks like B1-01 1E grounds the coil side of the relay?

So B1-01 1E is one of the contacts for the factory a/c button? Routed through the fan speed switch I take it?




It's weird because when I look at the FSM, (in your modified one, it is page 57 (Z-68)),  it looks as if the factory a/c button closes the circuit between terminals 1G and 1I




My problem is that the previous owner did the entire wiring for the A/C so I have no clue how it is set up.  All I know is the big rocker switch on the center console kicks on the compressor.


I guess what you're saying is that it's not as easy as simply transferring the wires from the rocker switch to the factory button?

[halfspec]

Alright. Since you're interested and because I'd like to have a place I can point other folks who are interested (I get this question in PMs often) I'll give you the long answer.

To start with you've got two diagrams that Pez put on this forum a few years ago:


This is the diagram to use when the stock fan #1 relay is in place.


This is the diagram to use when the stock fan relay is removed.

Concentrate on the AC request relay and note the subtle differences between the two diagrams.

Here is how they're different.
When you DO have the stock fan #1 relay the AC button gives out 12V when it's not pushed in and GROUND when the button is pressed in.
When you DON'T have the stock fan #1 relay the the AC button FLOATS (like nothing is connected) when it's not pushed in and GROUND when the button is pressed in.

Here is WHY they're different.
The AC button connects to the stock fan #1 relay on the ground side of the relay's coil taking a path through the thermo switch, X-07, etc. See pages Z-68 and Z-42. The reason this is significant is that the relay's coil acts as a pull-up resistor. In essence you have a weak connection to 12v through the relay. That's why you see 12v when the button is at rest when fan relay #1 is still connected to it. When the relay is removed/deleted that weak pull-up is no longer there so you get a floating connection. That simple change is enough to redesign the ac request relay circuit.

Now lets clear up the FSM mess on Z-68. IMO, this is one of the hardest parts of the FSM to understand. so don't feel bad that it's confusing.

Alright, pull up Z-68 and find the AC switch on the lower right. Notice that it's normally open. See the leg that exits out of 1G. That's the path to ground. How? You'll see it make its way to position 1 of the blower switch. When you switch the blower switch, this is how it gets ground.
Position #1 = Direct patch to ground through the switch
Position #2 = Path to ground through the diode then to through the switch
Position #3 = Path to ground through the diode then through the second resistor then through the switch
Position #4 - Path to ground through the diode then through the second and third resistors then through the switch
My theory on position 3 and 4 and the resistors is that the resistors are very low resistance (like 1-2ohms so they're negligible). The first resistor is a little more substantial therefore the diode path is there to shortcut it in position 2, 3, and 4.

So, you've got a path to ground through the AC switch on leg 1G. What about Leg 1l?

Leg 1l is the extra tricky one. You'll see it goes through the thermo switch then branches to the fan relay #1 then to the CPU (which is where you Pez's diagram says to pick up the signal at B1-01). Ok so remember the AC switch is NORMALLY OPEN so it only passes ground when you press the switch. When it's not pressed is what's tricky.

Case #1
Remember what I said about the coil of fan relay #1 providing a weak 12v pullup? Well when the relay is in place, and the AC switch isn't engaged (OPEN) the relay's coil sends 12V to B1-01. Then, when you press the AC switch and the blower is at least turned to position 1 you get a GROUND to B1-01. That describes the scenario in Pez's first diagram. What people get confused about here is the 12V pullup through the fan relay #1. That 12V doesn't just go away so what happens to it? Well that's the concept that makes pullup resistors useful. When you've got a STRONG ground through say the AC switch it OVERPOWERS the weak pullup through the coil so B1-01 only sees a GROUND. It also activates the coil on the relay, making the relay close and start fan #1.

Case #2
This case is when fan relay #1 has been removed / deleted. The weak pullup to 12V through the coil is no longer there so when the AC switch isn't pushed in (OPEN) B1-01 sees nothing  therefore it just sees an an OPEN AC switch. No voltage, no GND, no nothing. However, the actual switch's behavior doesn't change so you get a strong GND when you press the switch.



Soooo in your case, if you wanted to use the stock AC switch with as little mods as possible, you would determine which diagram applies to your situation (whether you have the stock fan relay #1 or not), then you'd build the AC Request Relay (no need to bother with the Compressor Relay), then you'd either hook the wires to the rocker switch to pins 87a and 30 (in the case that you DO have the stock fan #1 relay) or you'd hook the rocker switch wires to pin 87 and 30 (in the case that you DON'T have the stock fan #1 relay).

Hope that helps.

Lane

[halfspec]

Part #2

I realized that I didn't answer one of your questions with the mega reply above.

Why not just use terminals 1G and 1l as switch contacts?

1. You'd bypass the protection of your thermal switch and the security of knowing your blower motor is running. Without these two features you'd be begging for an iced over evaporator.

2. You don't know how the PO wired that mystery switch, so it's very possible he's running the compressor directly though the switch. While that's possible with a beefy aftermarket switch, you DEFINITELY don't want to do that through the stock switch.

Lane

[spd]

Thanks for taking the time to explain that Lane. Much appreciated! I think I'm (slowly) starting to understand. Still not 100% clear but I will re-read what you wrote a few more times.


I will talk to the PO (we are friends but we live about 70 miles away) about whether or not the stock Fan#1 relay is in use. Hopefully he remembers!

My suspicion is that it's wired independently of any of the Mazda wiring. I think the way it is right now it does not use the thermal switch, but I will verify.


Right now the compressor can definitely be turned on without the blower being on, but I am very cognizant of the A/C when I'm in the car. I think the risk of me leaving A/C on without the blower is quite low, so I am willing to forego at least that portion of the protection.



I also believe the aftermarket rocker switch is going through a relay already, not direct to the compressor.  Either way, adding a relay to control that circuit wouldn't be a problem.


One of my primary concerns is with losing blower motor functionality if I intercept the switch.

Is the blower motor switch reliant on the 1G - 1I circuit?  If I were to intercept the wires at 1G and 1I, and let's say just cut them off, would I lose blower motor control?


Many thanks for all your hard work and help - not just in this thread but in all things A/C!!

[halfspec]

Is the blower motor switch reliant on the 1G - 1I circuit?  If I were to intercept the wires at 1G and 1I, and let's say just cut them off, would I lose blower motor control?

No, the blower circuit does not rely on the AC switch to function through 1G/1l. In fact the opposite is true. The AC switch relies on the blower circuit to work.

I can see you're still considering tinkering with the idea of accessing 1G and 1l directly to try and take over the function of your aftermarket rocker switch. I'll just go ahead and go on record again and say I think that's a bad idea. It doesn't matter if the PO wires the compressor directly through the rocker switch or not, it's just not a good idea because you don't know exactly what the PO did and you don't know the ratings of the stock switch and if the stock ac switch even works that way (the FSM sometimes over-simplifies things) when you isolate 1G and 1l.

The proper way to do it is what I described at the bottom of in my second post. That way you retain blower control and your thermo switch + you don't endanger your stock AC switch. I can appreciate that you know how to sequence your AC for proper operation and keeping it from icing over, but what happens when you friend/relative/gf drives it or the guy that buys it from you down the road? All that's required to do it right is about $5 in parts and the time it takes to thoroughly understand what I've posted.

Lane

[spd]

Yeah I definitely hear what you are saying. I am going to consult with him first and foremost to see if I can gain any insights on how it was wired.

I'm not in a rush to get this done.


I have no problems using a relay as additional security.


I just don't know if I can wire it the same as your diagram because  1) the PCM is not controlling the compressor   and 2)  i'm not sure if B1-01 1E and its respective circuit is still intact


I will check it out though, most definitely.

If I can actuate the coil side of the relay from B1-01 1E, then I can just connect the existing rockerswitch leads to the high side of that same relay


I could also run the RPM switch between 1E and the coil side of the relay, too, could I not?

[spd]

I guess it could be set up like this?

[halfspec]

Nope. The Rpm switches I know of don't "pass" a signal, therefore you couldn't pass the signal from b1-01. They only provide a ground within the acceptable rpm range. If you can't figure out what the rocker switch is doing and you wanted to wire it to pins 30 and 87 of the relay (that should work) AND add a rpm switch, you'd have to add another relay. I'll try and draw you a diagram tomorrow.

Lane

[halfspec]

Here's the corrected diagram:



Once you get a RPM switch in your hands you'll understand why it has to be done this way.

I just don't know if I can wire it the same as your diagram because  1) the PCM is not controlling the compressor   and 2)  i'm not sure if B1-01 1E and its respective circuit is still intact

1. The AC Request Relay's only connection to the PCM is on 87 or 87a depending on which version of the diagram you're looking at. That's the only thing connected to the PCM and it's simply a translated output from the relay to an input on the PCM. From my second post I said "you'd either hook the wires to the rocker switch to pins 87a and 30 (in the case that you DO have the stock fan #1 relay) or you'd hook the rocker switch wires to pin 87 and 30 (in the case that you DON'T have the stock fan #1 relay)." That entails that you're re-purposing pins 87/87a and 30 to handle your rocker switch, therefore there is no PCM input/output. Like the diagram you posted, this circuit becomes independent of PCM control.

2. So? If you can't find the wire you need at B1-01 then trace it back to X-07. If it's not at X-07 then trace it back to G-08 (At the thermoswitch (my personal preference for tapping the signal)). The wire is violet all the way from B1-01 to G-08. It's a piece of cake and I seriously doubt your PO took the time to the AC wiring all the way back to the switch...

Lane

[spd]

Understood. I will investigate.


Thank you Lane!