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Cadillac Repair/Dash Vents not working on 1990 Cadillac Deville

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Expert: - 6/11/2011


Question
I have a 1990 Cadillac Deville and when I turn on the a/c it blows cold air from the top vent onto the windshield and onto the floor. However, it does not blow from the dash vents.

I've been told that there is a vacuum line that comes in and gives the system vacuum. However, I have traced all the vacuum lines to the vent doors and the only thing I can find is something that looks like a vacuum pump under the glove box on the passenger side.

I'm curious to know, if this is a vacuum pump if it supplies the vacuum to the vent doors because I cannot find a vacuum line running from the engine compartment. And if there was a vacuum line, I do not see where it connects to supply vacuum for the vacuum lines to the vents.

Does this particular model come with a vacuum pump and does not need a vacuum line from the motor? Sorry for all the details and questions, I have been workng on this for a week and cannot figure it out, nor do I have the money to take it in somewhere right now.

Thank you, Danielle

Answer
Hi,

Many cars run vacuum pumps to operate the mode doors. It sounds like you have one and your symptom is consistent with the problem you present. Normally one line will run from the engine and another line runs to the heat/a/c mode.

As for your specific model, I don't have manuals that old, but it sounds like you are on the right track for diagnoses.

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Rob Painter

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Alarm system questions cannot be answered on this forum. These systems are not what I can answer. Without being physically at the vehicle and not knowing what kind of electrical service has been done on the vehicle, there is no possible way to give an accurate answer over the internet. My expertise is in Ignition/key based anti-theft systems. These issues include GM VATS (resistor chip in key blade) PASSLOCK (MRD)-ignition lock rotation based, no special ignition key and the PKIII Transponder (computer chip in key) systems. These systems are not alarm based and are integral with the starting of the engine. This is why I cannot diagnose alarm problems without physically looking at the vehicle: Alarm systems are a completely different annimal than ignition key/lock based anti-theft system. Many alarm questions come from vehicles 10 years old, and since older, many hands that had been involved over the years.I am an expert in all GM factory (ignition/key based)systems. Alarm system questions pose to many situations beyond my knowledge as to what has been done to the vehicle over the years. Some guy may have actually wired the stereo into the alarm system. Who knows? Over my past 30 years in vehicle wiring repair, I have seen unbelievable wiring disaters done by guys that consider themselves "mechanics." I have seen stereos and alarms intalled using surgical tape. I have seen modules burn up, un-fused circuits, wiring jambed between the doors and even lamp cord used for a starter kill. To answer alarm questions over the internet without examining the vehicle is like asking; What does it take to remove a dent?

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Education/Credentials-ASE certified. 11 years with a GM dealer and 17 years with a repair facility dealing with only the repair of theft recovered vehicles.

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