Heater fan only works on high . Switch is ok , what do i do now ??
 

I replaced the switch with a brand new one . Just happen to have a new one laying around . Checked all the fused . That did not solve the problem . Under the hood , there is a large enclosure on the passender side fire wall . The A/C pipes go into it . That looks like the blower area to me . There is a 5 prong electrical plug that connects to the right side ( the side facing the steering wheel ) . I check the voltage to these connections , and different terminals have 12V depending on the position of the fan switch . However , when I put the fan on high and unplug this connection , the fan stays on ?? I figured this connection was controlling the fan , but I guess not ??? On the other side of this fan enclosure ( facing the antenna ) , there is a metal bracket holding a small metal box that looks like a relay . When I unplug that , the fan shuts off . So replacing that box would seem logical right ? Others have replaced that part wasted thier money because it did not fix the problem . So... what do I do now ? Any ideas anyone ?

Thanks .

sounds like the blower motor resistor is bad

I agree with your diagnosis.

Cool , sounds reasonable . So I how do I test that theory ?

the fact that the blower only works on high is test enough, when the resistors go bad they go into default mode. On chevy and ford I believe default is high, and dodge its low. Pull the motor resistor out and replace it. Should fix your problem

Right on buddy , thanks . I will do that .

Wait a sec .......
 

Just some Im clear on this , here is the situation :

Heater fan settings low and medium do nothing . Hi setting runs on hi . Not all 3 settings make it run on hi . I attached pics of parts . You are saying that I need to replace the part with the twisted wires ( as pictured ) , and not the little metal box ( as pictured ) correct ?

When I unplug the thing with the twisted wires , the fan does not turn off . When I unplug the little metal box , then fan does turns off .

And if the thing with the twisted wires needs to be replaced , how in the &^$%& does that part go bad ? It looks like twisted wires , not a computer !

when you unplug the resistor (twisted wire thing), the fan doesn't turn off because it's already being bypassed because it's faulty.

STARMAN, what are you working on? Might help narrow down your issue a bit better. From the looks of it, you have an earlier 1st gen. Please always provide your vehicle details when requesting technical help. It assures that the information provided is specific to your vehicle.

With the older resistor packs, it is very easy to test continuity on all of the coils to make sure that it is operating properly.

Once you post your vehicle info, I'll dig up a wiring diagram for the blower motor controls and we'll get to the bottom of your problem.

Sorry , its a :

1992 Chevy S-10 Blazer 4x4
Automatic
A/C
4.3 Vortec
212,000

If I have more time later, I'll take a look at what might be causing the issue, but for now, I figured I'd get you the schematic.

Then dash switch is new , fuses are good . I checked and cleaned the resistors . Then I went to a parts store and they let me borrow a new resistor to try . A new resistor did not make any difference , so I did not buy it . Im not sure what to do now .

Could be the relay. Again, I haven't had the time to dig in and really analyze the schematic I posted earlier.

Problem Solved ---------------
 

Well , here is what happened .

After a crappy day at work , I was diving home on an alternate route . Notice a sign that said " Pull A Part " . So I decided to check it out . Huge salvage yard . All vehicles are raised up off the ground , and there is NO mud/dust ,SUPER cheap prices !!! WOW . Entire salvage yard paved everywhere . 30 day unconditional return on all parts including electrical ! So I grabbed that little silver relay box off a junked blazer ( I posted a pic a few entries back ) to see if it would help . What do ya know . $2.50 and my heater fan works on all settings now .

Now that its fixed , its time to ride !

I was mistaken then. Glad you got it figured out!

Hey guys, I've got a 2001 chevy blazer 4.3 V-6 same problem, heater fan only works on high. So far I've replaced the fan blower, the switch on the dash, and still blows only on high. I'm pretty good with doing my own repair work been wrenching on cars and trucks with my ole man since 1968. I can't figure out this fan blower I'm dumbfounded, any suggestions would be greatly appreciated.

Peace Droidxusa,
aka Joe.

My problem and current situation is same as above, should I go ahead now and replace the relay. Could it be that simple of a fix, I will try this and see what happens. Thanks for any replies or suggestions.

Peace Droidxusa.

The vehicle in question is much older than yours, but the advice is still sound. The blower motor resistor is at fault. This is well documented on the forum as a search for "blower+motor+resistor" will show. Do some reading up. It quite easy to change out. Of course, if you have the electronic climate control (numbers around the temperature dial and not just blue/red), then you don't have a blower motor resistor pack.

Thanks swartlkk, when I tried searching earlier today nothing was coming up even under advanced search, so I tried your suggestion above and found that many of us have had this resistor go bad.

Again thanks for listening/reading about my electrical problem. I replaced the blower relay and fan still only works on #4 speed setting, going back to advanced auto to get the resistor now will install it tomorrow. And yes my switch is just blue and red.

I'll report back tomorrow with an answer of yes the resistor was bad or no its something else.

Thanks everyone for looking at my post.

Peace droidxusa.