[Aeroflux]

Sometimes I borrow an Acura from the family. The climate control on it is awesome. Just turn the dial to set the thermostat to whatever temperature you want. I want to do this for my honda. Right now I have a bad three-wire A/C Thermostat.

First thing I need to know:

Is it safe to bridge the thermostat plug (Yellow/White wire to Blue/Red Wire) and run the A/C, cutting the ground with the A/C switch when the cabin is cool enough? Is there any possibility the evaporator channels will freeze, crack and flood a sealed cabin with freon gas?

A/C wiring layout for my 95 EG

Second part is a bit more complex, more brainstorming than anything. If I understand it correctly, the climate control in the Acura is nothing more than a digital thermostat wired to a rheostat control. I realize that it won't be as easy to control heat, but for now I'm just thinking of having an adjustable A/C cut-off point. Something similar to this, or this, or this.

Thoughts?

 

[xile6]

Yes and no. Jumping the wire is kinda bad because if it doesn't get turned off at the right temp it will ice and leak like you said. I would keep that intact.
On the digi temp setup yea its possiable and you r on the right track.
So it all can be don't just some wiring to do. And you need a good temp switch

 

[Aeroflux]

What about running a simple thermometer to a digital controller? Wouldn't a temp switch open on a set temperature, or is that a wrong guess? What about a controller with temp probe wired into the A/C switch? Now that I know that the standard thermostat needs to be in the evaporator to keep it from freezing it changes things up a bit.

For instance, I need a more powerful fan to expand the cooling capability, less airflow will trip the stock a/c thermostat quicker...I think...and the cabin will be hotter as a result. Hmm...if there was a rheostat in place of the standard fan controller then one could really diversify the range of speed, and cooling as a result...that wouldn't be so hard to do, if it's just a simple stepdown of power. Replace the fan blower resister with a 12V rheostat, but what about amperage....looks like it runs on a 30A fuse...so it would require a Rheostat that could hold 30 amps? Possibly more if I can find some way to upgrade the blower motor...or just replace it. Looks like some Acuras share the same blower motor.

 

[xile6]

Yes the blower controls is just a set of resistors, but that same control also loops back into the compressor to cylce it on and off depending on what the blower motor is set to. I.e. fan on 1 might mean 75*, fan on 4 might mean 60*.
But as far as the evap temp switch goes. You first need to find out what is the lowest
temp that it trips at. And then you will go up from there. If the evap gets down to 40* before it trips the thermostat, then you need a switch that will trip at 40*. Then you would adjust up.

And it all depends on the temp switch. If you have one that outputs at a programed temped then yes. I.e. you set it for 60* and when it hits 60* it outputs a ground(or power). Then you could use that to trip a relay for the thermostat, it would then cut off the ac compressor till the temp with up.
The only thing with doing it that way is you will get a false temp. The evap is much colder then the temp out the vents. So setting it to 60 might mean 70* out the vent. It would take some getting use to and they would have to be an override so the temp doesn't get set to low.

I could probably help with making the wiring. Its just right now I'm replying from my cell so I'm not at home with my diagrams and software.

But just know fan controls are tied into temp on the civcs.


*edit
Also explain what all u want from this system. Could be over thinking the whole thing.
If your wanting to hit ac and set temp. Then all you might need is just a digital temp controller and some relays
The ac would be wired up that when it come on the fan spend would be 2 and then you set the temp and it will blow out cold air till that temp relay is triped. Then it could cut the compressor and just blow out air till the temp goes up, then the compressor would kick back on. Migt need a time delay so the compressor wouldn't be cycling on and off to fast.

 

[Aeroflux]

First of all, thanks for offering this much advice from your cell phone.

The original idea was to prepare the system to take over heating and cooling with a digital controller with a rheostat control and a target digital temp display. The heating part will be more difficult as the manual heater function needs to be converted to automatic through some type of servo. But for now I'd just like to focus on the air conditioning.

I've learned most of my electrical knowledge in bits and pieces, on computers, hobby cars and airplanes, and from fixing various problems with my car. I don't understand exactly how the thermostat functions. Two 12v wires feed into it, and one wire feeds into the A/C switch>fan controller>ground.

Since I just learned the fan controller also loops into activating the a/c compressor, I studied the diagram to attempt to figure out how. Since the Black/Yellow wire does not have a diode on the circuit, perhaps it sends a reference voltage to the ECU. Is that close?

This is another diagram of the Heater Control Panel. I figured I should post it since my pdf manual for the same generation car has multiple discrepancies (i.e. two wire thermostat instead of three wire)

I'm always trying to overthink things, to be prepared as I am prone to making costly mistakes. For instance, just last night I toasted a heater control panel pcb trying to bridge both the Yellow/White wire and the Black/Yellow wire to the Blue/Red wire. Fortunately I had an extra pcb and replaced it.
:3dtard:

Edit: Looking through the manual the thermostat test states that it should power a test light at 37 degrees and less (open) and come on at 39 degrees or more (closed).

 

[xile6]

not a 100% sure on how everything works. Didnt get to much into the ac wiring. But on the fan speed controls, they just us a different resistor to ground to change the speed.
easiest thing to do would be to leave the system stock. Then add your digital temp control to the ac clutch. So once the temp you set is reached then it would kill power to the ac clutch. Once teh temp inside goes up your digital temp control would feed back power to the ac compressor clutch wich it would then start bad to cold down everything. While all this is going on the fans would stay on.
And the ac button itself would be relay into your controller so that when you turn your controller on jumps the stock ac switch on the cluster.

For heat either live with sliding the cable or find some kind of motor that would work. and the heat would be a different circuit. It would have to turn off the fan speed when the temp got to high

 

[Aeroflux]

That sounds like a good idea. I still need to find out how the fan controller cycles the compressor though...and if there is a stepped temp reference voltage from the thermostat then maybe I can intercept that and use it somehow. But I'll need to get a new thermostat to measure it, and right now it's looking like I'll have to scavenge through the junk yards. Honda's warehouses are back-ordered and local stores don't carry it at all. I also need to replace the fan motor to take it out of the equation of any possible problems to cooling the cabin fast. Thank you for all the help!

 

[xile6]

I believe the fan is just controlled by resistors to ground. It cuts the compressor off by temperature. i.e speed 1 would more very little air so the evap would stay colder. Vs fan speed 4 which moves a lot more air but also warms up the evap.

Best thing to do is going to be to get your system up and running and then do some checks. But to get what you want its best to piggyback off of the stock system, then make a whole new one.

 

[Aeroflux]

That makes sense, I should have put the two together but I thought there was more to it. I just found some information via a DIY thread on the type of thermostat the 95 civics have:

"Hondas circa 1995 use an electrical sensor (a thermistor) and electronic switch (a transistor and more). The thermistor's resistance changes with temperature, electrically causing the transistor switch to open or close the compressor circuit. The c. 1995 thermostats have a three-wire connector, with the third wire being a 12-volt power source to allow the transistor to be a switch." (Link)

This explains why there are two 12v sources for the a/c thermostat. I'm only guessing, but perhaps the transistor is grounded (activating the a/c compressor) when the a/c button is depressed on the control panel. When the Thermistor reaches a certain temperature it must trigger the transistor to switch temporarily, until the thermistor gains enough resistance for the transistor to switch back on...I think...this is a little beyond my current understanding of electronic circuits. :wacko:

 

[xile6]

dont know to much about transistors. Just found out what they can do a week ago when i started to make my push button system. But i do know that they have 3 legs. 1 and 3 are normally a pass through and 2 is what controls if it passes through or not.

And to tell the truth it might just be easier to go to the ac switch on the ecu. I believe it outputs a ground when the compressor is suppose to run. So all you have to do is relay a ground in there with a diode. So when your temp hits preset it breaks ground and turns off compressor. But im just not 100% sure if this will work at all times.

But what would work at all times. Would be to cut the ac switch button. and relay that. So when your temp is reached it would be as if you just pushed the ac button which turns off the compressor.

Then blower speed would have to be a Rheostat that could hold 30/40A. Or just keep the 4 factory settings. Use a turn dial that would work like a dizzy cap and rotor. Each cylinder would output to a different speed. And the rotor would be the main ground. get what am saying? I know how it is in my head but putting it into words is a little hard.