As the title says, my heat (and air conditioning) isn't working correctly. The air blows out of the vents on all the low settings, but once i switch it to the highest speed, it doesn't work and the air barely comes out of the vents. It works perfectly fine on the low speeds, just not the highest one.
I searched and did not find anything. Do you think the switch isn't working right?
Thanks

Does the fan sound like its running when it's on high? Open the hood, pull the fan motor cover off and take a look, only about a half dozen 7MM screws. If you have never had the cover off, chances are good that it needs to be cleaned of debris that accumulates there. While the cover is off, you can check the fan operation visually.

[This message has been edited by jetman (edited 02-05-2011).]

Yes, the fan does sound like it is running, but very very slowly and quiet. Just for clarification, you mean the front hood right? I've never had the fan motor cover off, and never cleaned it out. But I'll check that tomorrow when it light out.

Here's a basic overview on how the blower motor controls work.

The three lowest speeds are controlled by a set of resistors. When you turn the knob on your HVAC panel (Low, Medium 1, Medium 2), a 12 volt signal is sent through a set of resistors (this is the same set that can cause cabin fires if not cleaned regularly), and depending on where the signal enters the resistor coils, a different voltage output is sent to the blower fan. The lowest setting sends voltage to the very beginning of the resistors, so the voltage is tapered the most, and the fan motor see's the lowest voltage and therefor spins the slowest. The medium settings connect to their appropriate points on the resistor circuit and output the correct voltage for the fan to spin at the different speeds. The 4th and highest setting, trips a relay which sends a full 12volt signal to the blower motor, and the fan spins the fastest.

Schematics:




It sounds like the relay has popped. It's located in the middle of the front compartment.

I had this same problem on my 87 S-10 years ago. I took that relay out and carefully sanded the contacts. Tried that a few times. I could not keep it working. Finally caved and bought a new relay. Worked ever since that.

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Rodney Dickman

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quote Originally posted by Rodney: I had this same problem on my 87 S-10 years ago. I took that relay out and carefully sanded the contacts. Tried that a few times. I could not keep it working. Finally caved and bought a new relay. Worked ever since that.

Rodney that makes you sound as cheap as me.