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I have a 95 Deville and in November I noticed that my cruise wasn't working and the outside and indoor temp had dashes instead of numbers like the picture shows. Now that it is winter I've noticed that the heat doesn't do hardly anything at all. The defrost light is lit up and every once in a while when I start my car the interior temp will say 75, but then will go back to the dashes. Any ideas? 

HVAC control.jpg

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Hmm....these can be tricky to figure out. Several possible issues.

All the computers are tied together on a network....circuit 800. This way they can share information. 

If one of the computers messes up....the data becomes corrupt. You start getting issues like "--" displays. 

If you check....good chance you are getting some "loss of data" system codes. 

When this happens the IPC will go into defrost mode and you get "--". Kind of sounds like what yours is doing. 

So it can be a bad IPC......you would need a Delco Radio / speedometer shop to check the IPC. A contributing issue is dashes "--" to them is a normal test mode.....so kind of extra hard to detect if it is a bad IPC. 

Or....one of the other computers on the network is messing up. It looks like the fuel data is still valid....maybe just a bad ACP. 

I don't remember....but I think the ABS unit is on the network. These were moved from the trunk to under the front of the car. They are known for the plug in to be rotted from corrosion. It would be worth a checking out the ABS unit out front. 

Have you checked for system codes? Hard to diagnose these from a keyboard. 

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There is a way to check the codes of each system.....it will likely take you several tries to see all the codes.....and be ready to write them down. See...


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Sounds like the ACP unit is dead or dying....saw this on another site.....it was easier to paste it....kind of sounds like what is going on.


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