Had our first overnight low in the 50's this morning, so I decided it was time to test the operation of the heat/defroster, before the colder weather later in the year in my 2003 Impala. the heat was good and warm, BUT it only comes out the floor and dash ducts, it won't come out of the defroster ducts. What is the issue, and what do I need to do, to fix it?
The mode switch is a rotary vacuum valve that directly applies vacuum to the appropriate vacuum actuator. It sounds like it's not switching vacuum to change from vent to any other mode.
All I know, is when I had it in the defrost setting it was coming out of the floor and dash ducts, not the defroster ones. I've not touched anything on the HVAC system
Nope, I checked vacuum lines from the floor to the engine compartment and they were all ok. Looking like I will have to go ahead and pull the trim piece out and look at the back of the mode switch. Have to replace the fan switch anyhow as it only works on position
4, and 5
Update: Was looking deeper under hood yesterday and found a vacuum line broken. I slipped a piece of hose over it, and now the mode selector works. Just have to fix the blower speed switch as it only works on positions 4 and 5
The speed control issue is usually what's called the blower motor resistor. In some cases, they actually contain resistors; in other cases, it contains a more sophisticated electronic circuit for controlling the fan motor speed. Either way, as long as you get a "blower motor resistor", you should be fine.
Looking on Autozone's website, most of them are around 40 bucks, but there are two outliers: one at 12 bucks and another at 94.
The resistor is located near the fan, up above the passenger's feet, against the firewall.
^+1. Again, on my old Fords, underhood vacuum breaks/leaks were common. Think age and engine heat/cold. Also, with a faulty/burnt blower motor resistor, blower fan only worked on high speed(s). Mode (vent) selection was controlled by vacuum, temperature was controlled electrically via the temp blend door actuator motor.
My leak was in the thin black vacuum line from the manifold. It was in the area below the fuse/relay boxes.
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