A/C gas indicator light

Here's a good look at another z31 engine bay --- especially the FPR. I think there's little doubt that my photo is of the fuel temperature sensor plug. And if you look really close, you might pick up a bit of the yellow color of the wire that's within the black protective sleeve.

You mean like exposing your A/C system to atmosphere? draining lubricant from the compressor, and compromising the entire system to corrosion?

Fix it, or delete it.

I just looked at mine and confirmed that the connector has been replaced, and I'm pretty sure I did it because it has shrink over the splice. The earliest picture of my FPR that I can find (about a year after I bought it) has the spade connector already on it, but the splice had just recently been done and didn't have the shrink tubing on it yet. I confirmed that it has a solid yellow wire as well, which matches the FSM wiring diagram (EFEC-8 for me), so I'm satisfied MINE is wired correctly.

It is interesting that the wires to the pressure switch on the manual A/C are yellow with a blue stripe and yellow with a red stripe. Mine have the stripes running lengthwise down the wire… in the picture above, your "yellow" wire is actually yellow with a red stripe (maybe it might be called a red band since it doesn't run lengthwise with the wire). That seems odd, but maybe the '85 yellow wire isn't solid yellow.

If you figure it out, please post up what you find… I'm really curious.

You don't delete A/C in Texas… it will get fixed when I have the funds…

Let's keep in mind that one issue here is why grounding out the fuel temperature sensor circuit should somehow make the GAS warning light go out. Here is a quick scan from my FSM of page EF & EC 8 --- it is the only wiring schematic I can find that clearly indicates the fuel temperature sensor. Note that the color of wire going to it is simply identified as YELLOW, no stripe color at all. Well, wbn noted that my wire actually doesn't have a stripe, just red bands. Nissan might think this as just being yellow. But the real issue is that if you follow it in the schematic, you can find it connected to some A/C wiring as well. It appears the two systems are somehow electrically tied together.

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It's somehow tied into the Pressure Regulator control module. Under ordinary conditions this may not happen (the GAS warning lamp going out), but with all my A/C components gutted there might not be other circuit paths for the signal to travel along, and the temperature sensor to ground may now take priority. (Ever notice how some car tail lights change in display brightness when one of the bulbs is out and they step on the brakes? … something like that might be occurring here. When one piece of the circuit is missing, the signal may use another path to ground.)

The signal that goes to the FPR temperature sensor originates in the ECU, and there should be nothing common with the A/C wiring. If I read the schematic for the A/C circuit correctly, the pressure switch removes potential across (and therefore current through) the "gas" light by connecting on the ground side of the light circuit.

The only way to turn off that light is to either remove voltage supply or remove ground (i.e. parallel path for voltage to ground). If the wire to your FPR is doing either of the two, it must be the latter. I would bet a soda that if you remove the plug at the ECU and test continuity for the signal to the FPR, you will not find it.

Assume the word "can" was supposed to say "cannot"… at least, I cannot find a connection.

It shows a connection to the pressure regulator control module (in my schematic above), which I believe has something to do with A/C circuits.

"The only way to turn off that light is to either remove voltage supply or remove ground (i.e. parallel path for voltage to ground). If the wire to your FPR is doing either of the two, it must be the latter."

I agree. But it is through another mechanism that the bulb light is being disconnected in some way. That other mechanism could be a circuit that, due to the A/C components and switches no longer being present, is now grounding through the Fuel Temperature resistor I installed. And is tripping a switch that is opening the bulb circuit (somehow through components still wired to the pressure regulator control module). It's fooling the Freon pressure circuit/sensors into thinking the Freon pressure is OK.

That's the best theory I can come up with.

Throwing in the towel…

I missed that tie point in the schematic you scanned. My copy of EF-EC-8 does not show that same wiring. I downloaded the '84 and '85 schematics from xenonzcar.com and neither of them show that connection to the pressure regulator. What model year is your manual from? It is conceivable that the '85 I downloaded is actually copied from the files for '86 because they appear identical. However, '84 is different in some respects but quite clearly shows the same routing for the fuel temperature sensor - a single yellow wire to pin 15 of the 20-pin ECCS connector.

Regardless of the above, it isn't logical to assume something related to fuel (i.e. temperature) would be tied to the A/C circuit when there is a fuel pressure regulator that the very same sensor would be attached to if you had it. That FPR is controlled via a solenoid which is wired to the ECCS. Furthermore, refrigerant pressure isn't regulated per se, so that nomenclature would not even be used. The only tie to the ECCS from the A/C is to kick up idle on load signal from the HVAC fan switch (not the refrigerant pressure switch).

Just to round out my efforts on this, I did double-check my own wiring. The yellow wire on my fuel temperature sensor is enclosed in a black plastic sheath, and I had to cut some of that away to find that it also has red bands spaced about 1 inch apart. However, I could not cause my GAS light to come on by disconnecting it from the FPR. The light does come on with the bulb check the first time you turn the ignition to "ON", but then it goes out when I start the car. I don't understand that, since (as I said) my system is open and the wires to the pressure switch are disconnected.

I'm done… hope you solve this mystery… it would be a great learning for both of us (and maybe others as well)…

My FSM is that of a 1985 model year; I purchased it from the dealer where I bought the car. It agrees with your pin location (no. 15) on the ECCS connector.

Perhaps the only way to make the little light come on is to remove all A/C connectors to the compressor and associated sensors throughout the system (completely unplug everything), as I had done … and then pull the fuel temperature connector off the FPR. But that would be too time consuming and I don't think worth the effort at this point. You may even have to discharge the entire system of refrigerant; I'm certainly not going to ask you to do that. I will however pose this to my friend who is an electrical engineer and see if he has any thoughts. In the meantime, I guess it will just have to remain one of those little enigmas about the car.

I would be interested if anyone else has completely gutted their A/C system (1985 GL) --- and then have them unplug their fuel temperature connector to see if the GAS warning lamp lights.

That's about all that can be done at this point. Thanks for all the conversation.