I have a 2005 G35X with about 110k miles. My father had this car for the last couple of years. During this time there was a radiator leak which was found to be due to a cracked radiator. Subsequently, and not sure if it is related, the car developed an issue with the air conditioning where the AC works erratically. It doesnt always cool i.e. the compressor doesnt kick in every time. It also shuts off rather quickly. I took it to the dealership where they ran several 'tests' and after a few days told me it needs an air conditioner amp.

At some point during the last two years the fuel gague also started to malfunction. It doesnt go below half, even when the tank is completely empty. This has resulted in me being stranded on the highway once. The dealership said it needs the 'sender' unit, replaced both sender units, and it still does not work.

The dealership said they searched forums and discovered that this model has an issue with a ribbon that connects the audio system to the AC amp and 'fixed' that. Not sure if they did that but they claim they did; still no dice. Now the AC amp isnt in production, which means I need to get it from a junkyard or search ebay for it.

I am at a loss on what to do. Mechanically the car if A-OK. I can live with the malfunctioning fuel gague, but lack of an AC in the summer is a killer.

 

The easiest way to change your AC amp or temp control center would be to put an aftermarket radio kit in that replaces all of the old crap. The radio / temp control board and cd/radio itself are one unit in these cars and make it kind of hard to tack the problem down sometimes. I think I have a modified temp board in the classified section if you are up to self installing a radio or you can buy a ready to go install kit on ebay.

The fuel sending unit is a fun one to diagnose also. It has left and right fuel level sending units and a split fuel tank because of the driveshaft. The passenger side has the fuel pump, venturi, filter, and main sending unit. Driver side is just a sending unit. The only way I know how to test is to ohm it out while it's outside of the tank to make sure it reads correctly full sweep. On my turbo car I bought 2 extra fuel pump units from the Upull yard to modify. One worked but had dead spots, the other was almost completely dead. I would guess the contacts either wear or get varnished, I haven't really dove into it any deeper. Others here have said the gauge cluster itself can have problems too but I haven't seen that problem in any of my cars yet. When I had the "only see's 1/2 tank problem" I always reset my trip odometer and never went more than 300 miles before filling up.

 

Regarding the modified temp board: I am assuming it will work with the stock radio. Does this come with a new ribbon? Where can I get that ribbon? Might as well change that too while the whole thing in unbuttoned.

I'd be interested in the temp board. I have a mechanic who can do the install for me.

 

Isnt the AC control unit a separate unit form the radio in the 2005 model?

 

You have two separate problems, unfortunately the fuel gauge one is very common and is USUALLY the instrument cluster. However you should test for resistance at both the harnesses on the fuel pump sender and sub unit. Expected resistance values are listed in the FSM, it will vary between 3-80 ohms on the main pump for full-empty and the sub unit will be 3-43 ohms for full-empty. Leave the back seat off for a week so you have easy access to those harnesses. If both the harnesses continue to have the resistance increase but the needle stops moving at the halfway mark then you know that they're sending the correct information but the instrument cluster is screwed up and not moving the needle.

As for the AC, honestly it sounds like low refrigerant, usually when there's a problem with the AC amp it just won't work at all, but you said it DOES WORK SOMETIMES and regularly cycles on/off quickly which is a big red flag that you're low on R134A and the system is tripping from the low pressure switch. I would get a second opinion from an actual auto refrigeration shop before throwing any parts at the car. It's quick but they'll probably charge you 1 hour labor to throw gauges on the manifold and watch pressures while running the system.

Normal pressure is usually around 40psi for the low side a a little over 200psi for the high side.

You can also put the controller into diagnostic mode and test all the functions yourself without any special tools using the "diagnostic pedal dance" method. Steps are outlined in section ATC - Automatic Air Conditioner on page 52. If the compressor cycles on/off then it's probably a pressure issue. Here's a link to the FSM.

https://www.nicoclub.com/archives/in...e-manuals.html

 

At this point I can live with the fuel gauge issue by using the trip odometer and guesstimating fuel with known average consumption. I only posted the fuel gauge issue for full disclosure because sometimes these issues can be interrelated.

Regarding the AC the refrigerant has been tested by three different shops and found to be OK.

 

I would still put the system in diagnostic mode and run through all the variables, if the compressor clutch is NOT ENGAGING then pull the harness and check for proper voltage, the nice part about diagnostic mode is you know there won't be any cycling because the compressor clutch will either be ON or OFF for each various step of diagnostic mode and it's listed in the FSM which makes troubleshooting easy. If you have voltage then you have a bad clutch, if you don't have voltage you have a bad controller (or wires going to the clutch but you can also test right at the AC amp harness to verify).

Just out of curiosity do you have an aftermarket stereo? Also, did the AC work and then suddenly stop or is it a component that has never functioned properly?

 

Stock basic (not Bose) stereo.

When the dealership put it in diagnostic mode the AC worked but it worked no stop for 10-15 minutes.

 

Will the AC work on a cold day?

Will it work if you put it in automatic with the temp cranked down?

Will it work when set to a manual temperature?

Basically, are there any times when the compressor WILL turn on a function normally?

Does your display show the correct outside temperature?

What pressure readings did these different independent shops get while the compressor was running?