* The control panel itself: This is the obvious part – the unit with the knobs and buttons you use to adjust the temperature, fan speed, and air distribution. This panel *houses* some of the control circuitry, but it's not the "module" in the modern sense.
* The HVAC blower motor resistor: This is a fairly common failure point and is usually located behind the glove box or under the dash near the blower motor. It helps regulate fan speed.
* The amplifier module (potentially): Some 1990 Cadillacs, depending on options, might have a separate amplifier module for the climate control system. Its location would be under the dash, but precisely pinpointing it without the specific wiring diagram would be very difficult. This is less likely to be the main "failure point" compared to the resistor.
* The blend door actuators: These are small electric motors that control the mixing of hot and cold air. They are usually located within the HVAC housing itself, deep inside the dashboard. Access is difficult and requires significant disassembly.
In short, there's no single "climate control module" to easily locate. If you're having climate control problems, you'll likely need to troubleshoot the system component by component, starting with the simplest access points like the blower motor resistor and the control panel itself (checking for loose connections). A wiring diagram specific to your 1990 Cadillac Sedan DeVille would be extremely helpful for this process. You can usually find these diagrams online through automotive repair manuals sites or forums.
