When I turn off my 1990 cadillac deville there is clicking sound coming from behind the glove box.

Usually they are located behind the glove box.

It sounds like the flapper valve behind the dashboard that diverts the incoming air from outside air to AC cooled air is not working. The cable wire may have come loose. It's located under the right side of the dash. If it's like my 1989 - you can access it by removing the glove box... fairly easy to do, just open the glove box and remove the upper and lower phillips head screws, and gently pull the glove box out and unplug the wiring connector on the left side. Also check to see if the solenoid valve is working when you change from off to heat or cool.

The pcm is located behind your glove compartment. you may be able to lower your glove box, but most likely you will have to remove your dash to get to it . if you have anymore questions feel free to contact me

I have a 2000 deville dts that was doing
the same thing.The problem was the mode door actuator located behind and to the left of the glove box. There is only one there and it is about a 3"x5" black box. Disconnect the electrical connector, two 5.5 mm screws, a little wiggling and pulling straight out, and it's out.

Hi there:
On 1992 Cadillac Deville 4.9L SFI 8cyl the Engine Control Computer is located in front seating area, passenger side, under dash, mounted behind glove compartment cavity on firewall.



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lower left side on driver's side near the hood release.

behind he glove box

The BLOWER MODULE is located on the A/C EVAPORATOR housing located UNDER THE HOOD passenger side firewall. Has 2 electrical connectors. Mounted with 4 screw bolts.Hope this helps

Remove the glove box, you will see the relays, sounds like a bad ground.

you need to take glove box out. It's right behind three three 7mm bolts for the plastic piece that holds it in. two 10 mm nuts that hold it to the plastic piece. Should come right out with a little finessed force.