2000 Blazer Heater Controls

2000 Blazer 4wd, 109k miles. About halfway into work this morning I noticed my feet were still cold. I started playing with the heater controls and only the defrost and dash settings are working. The dash/defrost switchover takes a little time. The floor settings default to defrost only.

Earlier this year while troubleshooting the 4wd system, I noticed some of the vacuum lines under the hood were in bad shape. I checked this morning and at least one small vacuum line had collapsed coming of the brake booster. I disconnected it but there was no change in heater control operation. Before I take out the heater switch, I’ll splice in a new vacuum line and see if that helps.

Any other other suggestions or things to check would be appreciated.


Ed B.

Did some checking after work. No vacuum leaks and the heater controls are working. There are three vacuum actuators/motors under the dash, floor/defrost, defrost/dash, and recirc. The floor/defrost actuator is working, i.e. the rod moves when the control is changed between floor and dash. However, there is no change in air flow (all defrost) when the control is set to the floor position.

I’ll have to remove more of the dash to see how the actuator rod is attached to the heat/defrost blend door. Is it possible for the blend door to become detached within the duct work with no outward signs?

Ed B.

Just going to put this thread to bed. It looks like any repair is going to involve removing the entire dash to access the ductwork. I think I’ll invest in a pair of fuzzy slippers for now and take a look at it in the spring.