The drain is usually somewhere under the passenger compartment, often near the firewall, but it could be routed in several ways. It might drain directly to the outside, or into a drain pan that then drains outside. It's typically a small hose or tube.
To find it, you'll need to:
1. Consult a repair manual: A factory service manual specific to your 1989 Chevy truck model is your best bet. It will show you the HVAC system's layout and pinpoint the drain location.
2. Look under the dashboard: Carefully inspect the area under the dashboard on the passenger side, looking for a small hose or tube leading from the HVAC unit. This may require removing some trim panels.
3. Check the floor: Look for any damp spots under the passenger side carpeting – this could indicate the general area of the drain. Be aware, however, that a leak might indicate a problem beyond just a clogged drain.
4. Look under the truck: Once you've inspected under the dash, check the underside of your truck near the firewall on the passenger side. The drain might exit here.
Keep in mind that working under the dashboard requires some mechanical aptitude. If you're not comfortable doing this yourself, it's best to take your truck to a qualified mechanic.
