C5TRED

97 C5 Dual Zone A/C comes on some times. No lights no temp nothing shows up. Then all of a sudden it starts working everything good, shut off the engine and restart no A/C no lights no nothing. Fixed by replacing ignition switch!!!

bobs77vet

welcome.....when you turn it on manually does it work? or is this part of the mind of its own syndrome?

C5TRED

I did get from the DIC - 99 HVAC: No Comm. I have all four of the factory shop manuals and I cant if nothing on it. Yes it is part of the mind of it's own.

bobs77vet

so how do we know the interior temperature sensor is working?

C5TRED

Haven't checked it. I have no lights on any of the controls temp doesn't show nothing works. Its like it's unplugged checked the fuses and relay they are good, following the schematic so far every thing I check is ok.

bobs77vet

that does sound like a power issue doesn't it.....I wonder how the control modules interface and power these?

I am still learning these systems also

Amazing1

I may have a similar problem. I'd say that about 1 in 6 times that I start my 04 the A/C turns on ( judging by light in dash) along with the light that depicts air flow from the outside (again, this light also comes on).
I hardly ever use the A/C and when I do it works fine, so I know that I haven't been just shutting the car off with the A/C on. That would be too simple an explanation.

Any idea's what is going on? How to diagnose and solve this minor problem, but maybe this is the source of a drain on my battery when the car is turned off. Ideas?

midnight01

if you are saying when you start your car the hvac display is blank, then after a couple seconds or more it lights up, that is your ignition switch.
Mine did the same thing, I would start the car and the screen was blank like it had no power. I replaced the ignition switch and now it works perfectly.

Amazing1

Midnight - Not sure I would say that when I start the car the "screen" is blank. I would say that each and every time I exit (and turn off the car for the day) I make sure to turn off everything, radio, any HVAC stuff that I may have had on, etc. But now, sometimes when I start my car, I notice that rather quickly I start to hear the blower/fan is on, and when I look at the controls, the "lights" in the A/C power switch and also the one which means you are allowing air to come in from the outside, this buttons' light is also on.

Ignition switch, that is very interesting. I'm headed to the Dealership today for some nice new Mobil 1, so maybe I'll head over to the parts counter while waiting and see how much replacement would set me back. THanks.

midnight01

I would rather you not throw money at the problem, the ignition switch I think has nothing to do with your issue; its the Auto mode of your controls. There were times mine did that too but I set all the controls manually and did not use auto and also set up the memory. Do you have memory seats, mirrors, and such? if you have memory option the hvac comes on automatically based on your memory setting. I set all my options, then pressed memory 1 for 2 seconds.
Mine does not come on anymore: here is the excerpt from the owners manual
MEMORY can store and recall the settings for the
driver’s seat position, the outside rearview mirror
positions, telescopic steering wheel (if equipped), radio
presets, tone, volume, playback mode (AM/FM, tape
or CD), last displayed station, compact disc position and
tape direction and the last climate control setting.
2-8
The MEMORY buttons are located on the driver’s door,
above the power mirror controls. The MEMORY
buttons can store and recall settings for up to three
drivers. Use button “1” to store the settings for the
first driver, button “2” for a second driver or press
buttons 1 and 2 at the same time for a third driver.
To store your memory settings:
1. Adjust your settings for the driver’s seat position,
outside rearview mirror positions, and telescopic
steering wheel (if equipped).
2. Press and hold a MEMORY button. The light above
the MEMORY button will glow steady for one
second and then flash once when the settings are
complete. Then the light will go off.
3. Set the climate control temperature, fan speed and
mode settings, radio presets, tone, volume, playback
mode (AM/FM, tape or CD), tape direction and
compact disc position.
Your memory settings are now programmed. Any
changes that are made to the audio system and climate
controls while driving will be automatically stored when
the ignition key is turned off.
When first entering your vehicle, after pressing the
unlock button on your remote keyless entry transmitter
or a MEMORY button, a recall of your settings will
occur when the door is closed and the ignition key is in
the ignition switch. As the memory settings are recalled,
the light above the button will flash until the correct
settings are achieved, then glow for five seconds
when complete.
A memory recall can be stopped by pressing any
memory seat, mirror or steering column position button.
When your remote keyless entry transmitter has been
programmed to driver 1, 2 or 3, and you insert the key into
the ignition, memory will also occur. Drivers 1, 2 and
3 correspond to the order in which your remote keyless
entry transmitters were programmed. See “Fob Training”
in the Index for more information.
Memory recall will not work if the vehicle is moving.
Memory recall will be temporarily interrupted during
engine crank.

bobs77vet

after reading this the memory function was also was what i was thinking.....but if it works correctly it remembers the last settings upon exit and key removal.....maybe the "memory's" ability to recognize changes has faded away and it has a mind of its own.

Amazing1

Thanks again guys. I will re-set my memory functions making sure that the A/C and whatever functions I want are set to my preferences, and see if that solves this minor problem.

On a separate note. For those of us who don't do our own work, modifications, etc., is there anything else like the feeling of driving your car around after a new crankcase of oil has been put in? Still feeling that now an hour afterwards.

Ceedub53

bobs77vet

sure have your fuel injectors cleaned...new spark plugs...new shocks...new tires

C5TRED

My Car dose not have the memory package. I did read somewhere about the ignition may be the problem. When I start the car the A/C sometimes show's up and run's other times it doesn't show up but while driving down the road it will turn on and sometimes run until I shut off the car. Some times it will run for a while and then shut off while I'm still driving? It's possessed.

midnight01

Well, could also be the unit itself. The ignition switch being bad would tell if you start the car, and there is no lights on the hvac display at all, its blank. Then after a minute or less they decide to come back on. The other theory is the actual hvac control unit itself. If you press the button and turn off the ac and it decides to turn back on out of nowhere then the buttons could be sticking or going bad.

GCG

I would suggest to start by addressing the lack of communications with the HVAC Control Module. All these communications take place through the Serial Data Bus. The Star Connectors, located by the passenger's foot well, are very helpful when troubleshooting the bus.

If this is the only "No Comm" code you have, then you can troubleshoot it by opening the Star Connector 1 and then proceed to verify continuity between pin L from the Star Connector 1 and the corresponding pin in the HVAC Control Module's connector.

If the wire tests OK, double check the serial wire female pin in the HVAC connector to make sure it is not deformed and has a good grip. If not, you would need to repair it to eliminate bad contacts.

Take a look at the following schematic showing the link between pin L from the Star Connector 1 and the HVAC Control Assembly.

C5TRED

So I should look more toward the ignition? because I can jut turn the key to the on position and to lights come on not temp no button lights at all. They use to come on when turning the key to on.

C5TRED

Thanks I will check that for sure. Thanks for the schematic.

C5TRED

Thank you all for your input and taking the time to help me out. Very nice forum.