This is a weird question but I have an ECU that doesnt have an AC control so Im having to do some wizardry. Does anyone know what voltage the pressure/thermo switches are rated for? I think I have a way to get it wired up without using any ECU control but I dont want to over volt them and they wear out extremely fast.

 

Does anyone have an answer for this or does it even matter since its a switch not a load? On the OEM diagram both switches go to the ECU which makes me thing their a 5v signal but does the FC even have a 5v signal or is it all 12v?

 

i was going to say 12v? i think the ECU just sits on the ground of the AC system. so instead of that going to the ECU and then ground it just goes to ground, you should double check that though

 

yeah thats what im going to do is just ground it on the coil side of the relay but because thats 12v I wanted to make sure I wasnt going to over-volt it. Also my pressure sensor has a crazy ammount of resistance so Idk if thats because its old or because its been running over-volted in this configuration for so long. Just want to make sure because if my thermoswitch fails I am guaranteed to break something pulling it out.

 

^Are you referring to the A/C pressure switch that's installed on the A/C plumbing by the dryer? If so, that's not a sensor, it's just a dumb pressure switch. FSM should have the specs on it, so if you put an ohmmeter across it's terminals, you should be seeing either 0 ohms or infinite resistance (or whatever maximum your meter reads), depending on the pressure in the line. IIRC, the A/C pressure switch on an FC is closed at pressures above 20psi or so, and open below that. If it was replaced with a pressure switch intended for an R134A A/C system, it will be closed at pressures between 20~300psi or so, and open outside of those boundaries.

 

I looked at the FSM but unfortunetly it does not show anything. Also kinda figured it was supposed to show no resistance which is why im replacing it but because it has such high resistance I want to know if its supposed to take 12v because if not thats probably the reason why it failed

 

Here's the FSM page that shows you how to test the AC pressure switch. If there's no refrigerant in the system, it will be an open circuit. For reference, the 2.3kg/cm^2 pressure referenced below = 32.7psi

 

ok but thats not what im after. I want to know if that switch can take 12 volts. with the way Im going to have it set up that switch will shut the relay off at open pressure. but with 12v constantly going through it on the ground side I want to make sure im not over-volting either it or the thermo-switch and wearing them out. this has nothing to do with their pressure ratings I just need to know if they can take 12v and that issnt shown on the FSM.
What is shown on the FSM is those two switches (thermo AND pressure switch) were in series going to the ECU which makes my mind immedietly think they were just feeding a signal voltage which from my understanding is normally 5v (if the FC even has a 5v signal circut anywhere, im just assuming here because nothing says anything). If their only rated to carry 5V and im pushing 12 through them then I may have a problem. Heck I dont even know if this is something I should even be worried about but I'd rather ask it then not and risk the thermoswitch going out and me having to tear apart the dash it replaced.

and yes I know their both switches, not loads like a relay but I assume they have some kind of voltage tollerance.

 

Just a thought, why not measure voltage at the connector?

The pressure switch pulls it's signal from the same place as the fan sub relay (I'm assuming a splice. I haven't had the harness apart). It's the blue/orange wire in the FAC-01 connector behind the front bumper.

From what I've seen on our cars, all grounds (chassis grounds or signal grounds) are some type of black wire. Whether it's solid black or black/red. My assumption would be that Blue/Orange would be a power wire. Try measuring the voltage there. Here are some pics from the FSM





If you're real desperate, you could always find out how much amperage that thing pulls (barely any I assume) and measure the resistance. Then plug that into ohms law and backtrack to calculate the approx voltage. But that seems like a lot more work for no apparent reason

 

I would do that but sadly someone's already messed with the wiring on the circut so its far from OE anymore. Basically what he did was bypassed the thermoswitch entirely and used the pressure switch to ground the AC relay. as far as I know the way the thermoswitch is wired right now is it gets power from the AC button then goes straight to ground. it doesnt do anything to toggle the AC relay if the evap core freezes because its not in series with the pressure switch anymore. idk why the hell they decided to wire it like that so im trying to fix it but when I measure voltage coming out of that connector going to the thermoswitch it only reads 10V when the car is on and only 8V when the car is turned off which doesnt make much sense to me.