Expert: autohelp - 11/14/2008

Question
Hello, I am having problems with my heater on my 1989
Cadillac Deville.  For some reason the heater will start to
blow cold air if the outside temperature drops below 23 F.  
Above that it works fine....Is this some sort of electronic
issue, or do I need to change the thermostat, or am I
looking in the wrong areas altogether?  Thanks.

Answer
IS or HAS the CHECK ENGINE light ever illuminated while driving the vehicle and or has any other lights illuminated or any messages from the message display center ?.

What work or diagnostics of ANYKIND WHAT-SO-EVER have been performed on the vehicle trying to fix this problem ?.

The problem is most likely in the A/C-Heater PROGRAMMER which needs to be tested of which you can do with simple directives.

If you are mechanicaly inclined or know of someone who is, You will need a DIGITAL MULTIMETER, Simple electrical schematics, Test procedures and picture locations of the components within the system that is causing you problems of which can't be done on this website which only allows one picture. I do not have a website so you will have to e-mail: onlineautohelp@msn.com in order to obtain the information.