[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?

 

[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.

 

[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).

 

[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!

 

[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: