Cadillac Repair: Cadillac a/c heat problem, vacuum motor, c programmer

Question
My 87 Cadi DeVille blows only heat through the vents.  This is due to the fact that when I check the outside temp reading it reads -40 below.  I have replaced the a/c programmer (at the advice of mechanic) and the climate control panel, both to no avail.  My question is:
Could this problem be due to a faulty Ambient Temperature control sensor, located behind the front grill, driver side?


Answer
Hi Mark, You may have 2 seperate problems going on here. First off if the air only comes out the vents then you need to determine if the programmer is getting adaquit vacuum and if it is being sent to the correct motor. If it is then a vacuum  motor or sticking door is suspect. The air should default to the windshield with no vacuum to the programmer. If that isn't happening then I would definitely look closer at the doors. Useing a handheld vacuum pump could isolate a bad door motor. The inside temp sensor may be a problem if there isn't a change from hot to cold. With the car having sat overnight all the temp sensors need to be checked and maybe there is one that is 10 or more degrees differant than the rest. Replaceing that sensor might be all that is necessary to get temp. changes. Your car is very sofisticated in that you can read all the computor sensors through the dash without the use of a scan tool. If a scan tool was used it might give faulse information or not enough info. to help diagnose this. I would get your car to a Caddy dealer tech and he should be able to get this problem diagnosed and fixed correctly without wasteing more money on unneeded parts. Bill