Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Fan switch

I have a 99 Astro, the blower fan no only runs on low or off, no matter which setting I use, and the vent selector only blows to the floor, is this a relay if so which one; or is there something else that could be causing this malfuntion? The fuses I checked all looked good.


On the blower speeds, it sounds like two problems. The high speed blower motor relay no longer works for the high speed of the blower motor. And the blower motor resistor pack has burned out resistors for most of the lower speeds of the blower motor.

The vent control part of the problem might be due from a vacuum leak. Depends on what the default mode of the vent system is when vacuum is lost. Most default to the defrost mode. Not the floor mode.


Astro’s have a accumulator bottle for vacuum (hard to get to ,by radiator on right side) The vents are vacuum controled but the default position is defroster.

I have replaced control heads for both fan speed concerns (default resistor failure is high),and vent position concerns.

Has the engine cover been off lately? it is possible to snag some HVAC vacuum lines when putting the cover back on.

You can pull the HVAC head and see if all the lines are attached (they are in a plug but it can come loose)take a look at the accumulator,see if you see anything hanging free.

The speed problem is either the head or the resistor group, the vent position concern,could be vacuum source,HVAC head,vacuum motor,linkage,I kept a spare head for test purposes.