Heater FAn Controls

Please explain how the heater fan switch changes the fan speed. My heater fan only runs on low speed regardless of the switch position.

Ok, I have the same problem - but mine only operates on high, I have taken the controls apart to see if I could figure out the problem - but could find nothing wrong... another funny thing is - it seems all of the problems people have on this forum "I" have had at one point or another... these must be common problems!

I don't know much about why or how it works this way but I've dealt with this prolem too. Here's what I found, maybe it will help you. In 3 different brand new fan switches, all 3 the same brand, #, and everything and all bought at the same place, one did not work on low, one did not work on medium, and one started smoking and quit altogether. From what I was told the switches are just not "the right ones" even though they are supposed to be. You can buy different switches for your vehicle (which all say they are the right ones) and some are only meant to have 2 settings instead of 3. My take... keep trying till you find one that you are happy with!

I have an 89 w/ ac I unplugged the switch and sanded the contact Now I ahve all 3 speeds but still cant get the vent/heat/defost to switch. I do have vacumn to the thingy by the gas pedal any ideas

The fan speed is derived from a resistor bank mounted inside the blower case in the engine bay. The switch connects the fan to a different value resistor. The lower the resistor value, the faster the fan goes.

What can happen I believe, is the resistors, being made of wire in a coil, are sometimes crushed together and short, or corrode and break away.

A multimeter will be needed to determine if the resistors are still in circuit. The wiring from the switch can be tested too.

The switch can be defective too. The little contact shoe inside that moves from set of wires to another, can get stuck and break free, possibly staying on one set of wires, always. New switch then.

If you have vacuum to the vent actuators (motors) then the fault is likely to be the slider having jumped out of its track. A careful dismantling job is required for that.

thank you the acuator only moves a little im going to attemp to take it apart and try to fix it

I have a 94 Jimmy which had the same prob. I did find a correction though. What I did was buy a new switch AND a new plug. There is no wiring harness, you have to build it from scratch. The dealer had the plug and the connectors that are inserted. He was nice enough to crimp different colored wires to the connectors, then inserted them into the plug. I got home, changed the plug, one wire at a time, then put the new switch in ... it's worked perfectly since. Total cost to me was about $25.

One of the contacts on the original setup wasn't making a proper contact, and eventually burned the connection. I had fiddled with that switch for months before it finally just stopped working. Opened it up a couple weeks ago, found the burnt plug ... got all new stuff. Some glad I did!

--Jake