timjj

HI guys,
I have a 2004 350Z softtop and have had issues with AC unit since I got it.
The AC unit has 2 options - Cold (when set at 18 on the dial) and Hot when set to anything but 18. Makes no difference is AC button is on or off. There is no range. I have read it can be because of the sun sensor on the dash (no idea how that could be of any effect). I replaced the passenger side one but makes no difference - no surprise there. I have pulled the white AC control box out from under the stereo but everything looks fine. No broken cables, all lights and functions of the unit work - just the ability to adjust them temperature is stuffed. Anyone come across this issue before and been able to find a solution? Really annoying having either a hot or cold cabin and nothing in between!

Thanks!

Tim

icer5160

iTrader: (4)

Hi Tim,

If you're not getting an inbetween range, it could have something to do with the blower box vent valve. That vent valve opens and closes redirecting airflow between recirculate and outside air. If you're getting steady hot or cold when set to both extremes (max cold and max hot) then it sounds like both, your AC Evap core and Heater core are functioning as intended. This is where I would look next. Maybe the servo arm stopped working or broke somehow? It's fairly easy to access the blower motor housing. But before dropping it, I would suggest pulling up the battery cowling under the hood. From there you can visually inspect the vent flap/valve from the outside air inlet port. Make sure it's opening and closing in accordance with your AC controls. I'm not an expert with the Z's AC system beyond this. There could be other components behind the dash that work to together with the blower box to help manage temperature. I believe there are other vent valves/doors that redirect airflow. For example the front window defrost and foot well vent settings.
Hope this suggestion helps. Good Luck!
-Icer

timjj

Thanks for the reply Icer.
If I am understanding correctly, your thinking is that the valve might only be opening//closing fully and not in smaller increments - pretty much an on/off system?
I'll pop under the hood and have a look and try get familiar with it.
Thanks again, will post up what I find.

Tim

icer5160

iTrader: (4)

Hi again Tim,

Yes, that's the logic I'm following.

Found an older thread with some info regarding a similar issue. The more I read, the more I think you have an "air blend door" (or what I called a valve) causing your issue. But this thread mentions other components that could cause this issue. The sunlight sensor, interior temp sensor, and outside ambient temp sensor. There could be more than one "air blend door" . One I know for certain is part of the blower housing which I mentioned previously, but I suspect there is another "blend door" built into the vent system around the heater and evaporator core housing. The heater/evaporator core is located deep in the dash behind and underneath the radio and AC controls, lots of work to uncover.

Have you verified your vent controls are working properly (Feet, defrost, & main vents)? You should hear the blower motor slow down while the airflow is redirected.
Regarding a possible faulty sensor, I'm not sure how to go about testing these. I believe the ambient temp sensor displays information on the multi-display in the center dash (triple pod).
-Icer

Peterman

Hey Tim,

I have the same issue in my 08 350z. It started after I upgraded my head unit and had to deal with some weird wiring issues from the previous owner/installer. When the dial is all the way to the left (cold) I get cold air but even one tick towards the right (hot) I get heat; no middle ground. I haven't really dug into it since I run AC pretty much all the time here in FL, so I’m not sure if it was caused by the work I was doing or just coincidental. I’m going to start with Icer's suggestions but If you figure out what your issue is I would be interested in what the resolution was.

zakmartin

I can think of four things that could cause this (off the top of my head):

1. Bad potentiometer (pot) in the heater dial
2. Bad BCM
3. Bad blend air door actuator
4. Thermistor attached to the kick panel (below and to the right of the steering wheel behind the small scalloped opening) is bad or disconnected.

timjj

Icer - yep all the other features work without at problem. Purely just the temperature range. I have looked at the cost of a second hand a/c amp control box with is about $100 here in Australia - about $75 over there. Cant even be 100% that the module will be working correctly either but probably the easiest place to start.

Peterman - You have the exact same problem. I believe my Z had an aftermarket headunit before I got it although they put the original back in. I have since swapped out for an aftemarket also. I will let you know if/when find a solution.

Zak - thanks for those options. I didnt even know what a few of those meant (thanks google!). Ill add them to the list and get cracking at it all over weekend.

Appreciate all the feedback guys.

icer5160

iTrader: (4)

The AC Amp control box is cheap enough to take a gamble on it in my opinion and replacing this unit has been a common solution to many AC control woes. I've seen threads talking about a loose harness connection to the AC amp causing all kinds of weird things to happen or sometimes the wiring was damaged by an aftermarket headunit install.

To debug something as complex as the AC system, you would need a dealer level scan tool. I'm not sure how much diagnostics fees are in Australia, but this might be a viable course of action before throwing parts at it. So far I don't see any clear red flags if the "air blend doors" are working properly. Still, do your due diligence and check the wire harness around and connected to the AC amp. If this has been taken apart more than once, it could be related to your issue.
Keep us updated!
-Icer