Forums/Z31P/z31-basics basic-modifications-basic-questions-aka-the-newbie-forum/A/C gas indicator light
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NewJerseyZ: (2014-10-09 00:06:00)
A quickie here … I've removed my A/C system (completely) in order to adapt some of my mods, but now there's an annoying red light that's continuously on located on the top left of my center console, near the temperature setting slide lever. No doubt it's detecting a low amount of refrigerant pressure. Is there a simple (non destructive) way to have this light be off --- for good?
1985 Turbo 5-speed GL
Thanks.
Trbulnt: (2014-10-09 00:18:38)
As far as I am aware there is no low refrigerant pressure indicator on these cars. Solution is to remove the control console and remove the bulb.
les_joey_paul: (2014-10-09 01:17:31)
probably just jump that switch [archived image: redface.png]
Rick88ss: (2014-10-09 01:42:43)
Press the button and it should turn off.
NewJerseyZ: (2014-10-09 01:59:52)
It's a button/switch? That's news to me … but hey, I'll try it.
It is a very tiny light … we are on the same page, right?
Here's a photo of what I'm speaking of …
Gas Light.jpg
It's that little bright light to the left of the A/C switch/button.
It stays on all the time now. Pushing the A/C button in or out does nothing at all.
PS: There's also a cassette tape stuck in the player … any suggestions?
(That's why that arrow light is on.)
Trbulnt: (2014-10-09 02:32:18)
Well I learned something new! It does indeed mean freon is low. Makes me wonder where it gets its reading from and if its just a pressure transducer that completes a circuit with pressure in the system. If thats the case than it should be as simple as jumping that sensor to either ground or 12v depending of if its a one or 2 wire setup. I believe with all the questions you've had lately that a Factory Service Manual would be real handy for you to have.
NewJerseyZ: (2014-10-09 02:37:08)
I have one … imagine the number of questions I'd have if I didn't!
[archived image: rolleyes.png]
wbnethery3: (2014-10-09 05:23:18)
Based on the FSM schematic, it looks like a simple switch. You ought to be able to jump the wires to each other (assuming you can find them after the delete) to make it think it's got refrigerant. Of course, there are other things that may happen when you do that. Not sure what else that switch keeps from coming on… this is on page HA-30.
AC schmatic.jpg
Good luck…
NewJerseyZ: (2014-10-09 21:55:16)
It looks as though a bit of luck did come my way … thanks wbn.
My mods required me to increase my fuel pressure to 3 BAR, so I changed my FPR to a Nissan 3 BAR piece, but unlike the z31 unit, it had no sender for fuel temperature. I read somewhere that one can simply ignore it and just leave it unattached, the wire that plugs into the fuel temperature sender. The FSM (EF & EC - 50) shows that a working sender is a thermistor that when tested should have given resistances for noted fuel temperatures. Leaving it unconnected is basically like having infinite resistance, and higher resistances indicate colder fuel --- very cold. Colder fuel is denser than hotter, so to compensate the ECU is leaning the mixture, perhaps too much. So I wired up a fixed resistor of what I feel is for an average temperature range --- 750 ohms, for around 100F. Once I wired up the resistor and turned the engine over to start, I immediately noticed that the GAS warning bulb no longer came on. Pushing the A/C button on and off did not make it come on, nor did running the blower fan. Does the car run any better? … maybe, but at least the ECU doesn't think the fuel is colder than -20F. That's right, 20 below.
Why this works I have no effin' idea … but it did.
Totally unexpected.
Rick88ss: (2014-10-10 01:19:28)
Weird that now its off. Sorry I got confused with which light you were talking about. My 88 doesn't have it but I see what you mean in the pic. If it comes on again you should jump the 2 wires that used to connect to the pressure switch that was on the a/c drier.
NewJerseyZ: (2014-10-10 02:00:05)
I get it now … you thought I meant the light on the A/C button switch itself. I guess they dropped it (GAS bulb) in later years.
Thanks for the location of that switch. Schematics are great tools, but many times they don't give enough information.
wbnethery3: (2014-10-10 05:23:38)
Lingering doubts…
The FSM does also have a wiring diagram, I just didn't copy it since you said you have the FSM… I copied the schematic to show that the switch is a two-wire and can be jumpered. I don't buy that the gas light went off because you wired a resistor to the fuel temperature sensor circuit. On my car, that sensor grounds through the block on a single wire spade connector on the FPR, which grounds through the mounting screws to the intake manifold. My FSM for the '86 doesn't show the sensor on EF-EC-50, but on page EF-EC-71, so maybe there are some differences. Your resistance of 750 ohms would produce a fuel temperature reading of around 120 F according the '86 FSM.
My question is what did you wire a resistor to? You seem to know your eletrical fundamentals, so I doubt you missed this, but is it possible you wired a resistor to the two connectors for the A/C pressure switch? They're in the same general area of the car and might be confused with the spade connector for the fuel temp.
No matter…if you're happy, I'm happy… maybe that little bulb just burned out…
NewJerseyZ: (2014-10-10 17:53:23)
I pretty much agree with everything you said, but I'm pretty sure I got the correct wire. Here's a photo of the cut wire (and single spade plug) that was removed and replaced with the 750 ohm resistor … (I'm keeping this incase I should ever find a way to reconnect an OEM sensor back in line.)
FPR connector plug.jpg
Now look closely at the FPR from this front view; it was taken back when I was still using the OEM FPR. You can make out the sensor connector plug just above the spark plug wires. It's that same plug as in the previous photo. (I strongly doubt that wire could have reached anywhere near the A/C components.)
mgp Front Portrait.jpg
Here's the finished product. The resistor is grounded to the upper intake manifold along with another grounding lug. The one with the resistor is to your left --- rear facing and then snaking forward. The resistor itself is inside the heat shrink tubing being used as an insulator.
Fuel Temp Sensor Resistor.jpg
So it's on the correct wire (99% sure)… and it's grounded through the manifold as the original sensor was.
Now, the question is … does the light come back on when the ground is lifted? YES
It does not make sense to me either!
[archived image: confused.png]
wbnethery3: (2014-10-10 18:20:50)
Check the wiring color combination for the FPR temperature sensor in your FSM wiring diagram. I don't have mine (at work right now) but I'll look as well. That behavior sounds like it's simulating a closed switch for the refrigerant pressure. Being that yours is a different model year, and turbo vs. my NA, only other difference I forgot to ask about is whether yours had the automatic A/C or manual. The faceplate on yours is silver, mine is black so I'm not sure if that's just model year difference or also the auto A/C. Not sure if all those things matter at all, but better to know.
The other obvious way to confirm what you have wired the resistor to is to find the pin on the ECU for fuel temperature and test continuity.
Again, not sure it's important unless you want to know… I'm a little OCD and I sure as heck do. [archived image: smile.png]
wbnethery3: (2014-10-10 18:22:49)
Forgot to mention - that connector doesn't look anything like what would plug into the pressure switch on the A/C drier… it also doesn't look anything like what's on my FPR temperature sensor, but I think mine has been replaced with a simple female spade connector. I'm probably the one who did it, but my memory is a bit dodgy…
NewJerseyZ: (2014-10-10 20:08:43)
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.
88sinZ: (2014-10-11 04:20:55)
Again, not sure it's important unless you want to know… I'm a little OCD and I sure as heck do. [archived image: smile.png]
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.
wbnethery3: (2014-10-11 04:31:29)
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.
wbnethery3: (2014-10-11 04:35:21)
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.
You don't delete A/C in Texas… it will get fixed when I have the funds…
NewJerseyZ: (2014-10-11 13:28:42)
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.
img015.jpg
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.)
wbnethery3: (2014-10-13 16:50:14)
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.
wbnethery3: (2014-10-13 16:53:03)
… 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.
Assume the word "can" was supposed to say "cannot"… at least, I cannot find a connection.
NewJerseyZ: (2014-10-13 19:27:50)
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.
wbnethery3: (2014-10-14 04:52:12)
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)… [archived image: smile.png]
NewJerseyZ: (2014-10-14 12:27:41)
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. [archived image: smile.png]