Mechanical maggots--help with car fan

[Dexter Rutecki]

The fan for my heater/AC, that is. It only runs on the highest setting--settings 1-3 do nothing, but they do activate the AC compressor when the AC is supposed to be on. This just started, out of nowhere, a few weeks ago. I checked all the fuses and they're OK. What could be causing this?

[truth]

Gremlins.

[Mountainman]

maybe it's just a short. my truck did the same thing, i had to replace my switch. my buddies suby did the same thing, he replaced the switch. both work fine now

[Aldo]

Hey Dex,
Car and mileage? Could be time for a new blower motor.
sounds like a fan on the way out it it's a high mileage. I may be wrong bu the switch wouldn't activate the AC if it was bad.
This is all idle speculation.

[Mountainman]

true. i guess i don't know the extent of the switches on his car. on most vehicles i know, the knob you select what you want(ac heater vent etch) is one and the blower fan is entirely on it's own. but i'm pry wrong.

[Cornholio]

I doubt it's the motor. Don't these things work by just jacking down the resistance as you turn up the switch?

Sounds like you've got a short or a fray in the circuit that adds resistance when you turn the fan down.

But I'm a moron.

[Eldo]

I vote for a faulty fan switch. Usually things are wired so that the compressor comes on (if A/C is on) whenever you turn on the fan any speed.

The resistance part of the fan switch is probably screwed (in those lower speed settings), but the compressor still comes on because the power goes through a different part of the switch. (One that is either on or off, and doesn't vary in voltage.)

(At least that's how it works in the mid-80s vintage of one of my vehicles.)

What is this vehicle anyways? That might help.

[Beaver]

Another vote for the switch.

[basom]

i used to live across the street from click, or maybe it was clack. one of the tappit brothers from cartalk. he would know what your problem is. however, we both since have moved.

well that was a waste of everyones time.

[bagtagley]

The switch would be easy to test with a volt-meter. If that's not an option, another would be to borrow one for testing or get one from a junk yard. Unless it's domestic, it's doubtful that an auto parts store would have it, but that's another thought.

[tuffy109]

another vote for gremlins

[Ferniefreeheels]

Dex,

90% chance it is the blower motor resistors. It was a very common problem on GM/Chev pickups. I don't know what your driving but there are usually 3 or 4 resistors mounted on a board and probably bolted on the heater box somewhere. Your blower motor only has one speed, different speeds are achieved by switching the power source through the resistors. Good Luck!

[Dexter Rutecki]

Switch or motor--both beyond my ability to replace, was hoping it might be something easier. Which would be more consistent with it working, but only when turned to its highest setting?
'95 Altima, 130K.

[BobMc]

Dex,

Yup, as a few others have pointed out your blower motor resistor is shot. This is an electrical device that slows the current to achieve the lower fan speeds. High speed is directly connected to 12 volts, that is why this still works.

In a truck I'd imagine it to be pretty easy to replace. It'll probably be on the heater case, this is found in both the drivers side and passenger side footwell. Cram yourself into the footwell and look up and to the right if you are on the drivers side. You may have to remove a trim panel to see it. Look for wires going to a connector on the heater box. The resistor is usually held in by a couple screws. Once you get it out you can either test it with an ohmmeter or just buy a new one.

Most vehicles have them on the drivers side, but if you don't see it there look on the passenger side.

Hope this helps,

BobMc

Edit: This is what I get for skimming the thread ^

Dex,

Being as how it's a Japanese car I'm sticking with my diagnosis. Look around the heater case, you're sure to see it. I doubt an Altima has many stepper motors on the heater case, so it should be pretty easy to pick it out. It'll be one of the few electrical devices on the case.

Another edit: The resistor is on the passenger side, more or less behind the glove box. Easy to replace.

[DaveTV]

http://www.altimas.net/
Get the HAYNES...

[splat]

Feed the squirrel.

[Dexter Rutecki]

Thanks, BobMc and others. I will definitely look at that and see if I can replace it. If it was really going to cost money I was going to let it go and just deal with the fan either being off or completely on full, but hopefully this'll take care of it.

[trainnvain]

Come on guys, it's so simple, maybe you need a refresher course! It's all ball bearings nowadays!

[iceman]

Originally posted by splat
Feed the squirrel.

Yeah, right. That's about what I would have expected you to post. How can you talk about squirrels when it's obvious that it's the big rubber band that needs replacing?

[Dexter Rutecki]

At least iceman's been in the car, he's allowed to make fun of it. Splat hasn't earned that right yet.