It's as simple as that.
Allthough I'm afraid fixing it wont be.
The heater blower quit working a couple weeks ago (winter sucks!) and the other day when I shut the door kinda hard, it kicked on. SWEEET!! Well when I go to leave the next day, it dosent work again . Four days go by and nothing, then today my sister shut her door, and it starts working again? What is going on here??? My guess is a short somwhere, or that resistor thing is jacked up, or the relay. Just wanted to see if anyone else had delt with this and won the fight before I started dolling out the frog skins.



Thanks,
Max

 

I'd say a dirty/corroded wiring connector. Try pulling the connectors and cleaning as required. Just pulling and reinstalling will probably be enough.

Or, could be a broken wire that is making intermittent contact.

 

It's likely NOT the blower motor itself. The 4-position fan switch in the dash, it's wiring harness, the blower motor relay and the resistor pack are the usual culprits.

 

Yeah, I had a feeling it would be somthing like that, just wasnt sure. Guess I'll trace all the wires I can get to, and clean all the switches and contacts accesable, then go from there.



Thanks,
Max

 

Is the blower motor making any odd noises? Does it seem to be going slower than it used too? In the past I have had a car that the blower motor would sieze up and when you hit a bump real hard, or slammed a door, it would break free. Usually when you shut it off, it wouldnt come back on. I went the route of checking all kinds of things, even replaced the switch in the dash, but it was definately the motor.

 

I agree with lj.

It's probably not the resistors, because they are only active in the 3 lowest speeds. If the resistors were intermittent, high speed would still work. In fact high will work with the resistors removed from the car.

It's probably not the relay, because the relay is in one position in the high speed, and the other in the 3 lower speeds. It's highly unlikely that BOTH fixed contacts of the relay would fail in EXACTLY the same way, and would come and go EVERY TIME at EXACTLY the same time. While possible, I'd describe it as unlikely; I'd put the odds against that, as somewhere in the class of numbers that astrophysicicts use.... one of those mind-blowing ones like, 1 followed by 30 zeroes, to one.

A common no-high-speed problem is a certain very stupid connector in the big red wire, right directly above the pass side valve cover. However, when that burns up like it always does, the 3 lower speeds still work.

THe only thing that can possibly cause your problem, is either the blower motor itself; or the purple wire, either where it attaches to the motor or to the relay; or the black ground wire from the motor chassis to the firewall. Which is worth checking, as the motor can rust underneath that little blade connector, and become intermittent.

You can figure this out. Don't go trying to pay somebody, they'll just charge you for half a day of diagnostic time, and tell you they can't find it, and you'll be out $200 or whatever and no closer to a car that works.

 

I will reitterate that the 4 position switch and it's wiring harness can very well be the problem. My 91 Blazer had the exact same symptoms which, upon initial diagnosis, appeared to be a bad relay (if you tapped the relay box with your knuckle or hit a decent sized bump it would suddently turn on again). Replaced the relay but no joy- same symptoms at all fan speeds. I was in over my head so took it to the shop. Next day the guy told me it was the 4 position switch and it's related wiring harness- says they see this kind of problem quite regularly.

Wait till you have the problem appear again and do a few quick tests. First one is to jump the fan motor directly to the battery just to make sure it runs fine- should come on full blast. If it passes that test (and it probably will) then you know you're down to the electronics that supply power to the motor. That's when it gets complicated. This simple system has more stuff to go wrong that you might imagine.

 

This is the first thing to do in any case, because its the easiest to test. I wouldnt count it out though, its a good possibility.

 

as has been mentioned there are a number of things that can cause this.
on something like this the first thing i would do is hook up a test light to the power wire & to the ground of the blower motor & leave the test light on there until the motor doesn't work, if the test light is on you know you have power & ground to the motor & if its not running the motor is bad, if the light isn't on you know to look else where.
you can make your own test light for cheap, some tape, some wire like you get with new speakers that no one ever never uses, a bulb & socket is all you need.
i normally use a dash light (the small 194 bulb) & its socket, i solder the wire to the 2 tabs on the socket, put the bulb in & tape it up. strip enough wire on the other end so you can pull the connectors off & slid the wire into them & plug them back up to the motor. it takes maybe 10 minutes to make a test light & hook it up. make sure the test light isn't against anything that it could melt or burn.