de frost heater control

[p--sed chevy owner]

The vacum pump that controls the heater and de froster will only work in the window defrost and vent modes only. Looked at the vacum pump it moves when the knob is turned only in two settings. Should it move to 4 settings based on the control settings on the dash?

[BlazerLT]

Vacuum pump?

The controls run off of engine vacuum.

[ricksza]

Originally Posted by p--sed chevy owner

The vacum pump that controls the heater and de froster will only work in the window defrost and vent modes only. Looked at the vacum pump it moves when the knob is turned only in two settings. Should it move to 4 settings based on the control settings on the dash?

I'm assuming that you have C60 option HVAC.
You must be referring to the mode actuator under the dash on the heater box. There are two vacuum hoses going to it (yellow and brown). Yellow should have vacuum to it in all but the following settings: MAX, NORM, BI-LEV & VENT. Brown should have vacuum in the following settings: MAX, NORM & VENT. If one of these is wrong, you have a bad mode control switch.