Chev dash fan not working on high

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Bjwinspect

Bjwinspect

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Lynchburg Va
I have seen this problem in previous post, but have not been able to locate the answer I need.  In my 99 Aventurer with the Chev chassis, my dash fan will stop running on high after about 15 minutes, other speeds continue to work... if I turn it back on high after about a minute on another setting, it will start running again, for about another 15 minutes.  I know the slower speeds are controlled by a resistat  and high has a direct connection.  I tried changing a relay under the hood on the outside of the blower housing, but this does not correct.  The resistat  is also in same area, if I unplug the resistat the fan does not run on lower speeds but willon high so it is apparent that the high circuit does not go through it.  Does anyone know where the relay that controls power to the high setting is located? I think that is my problem... or does anyone have other ideas?
 
the blower motor typically has a direct connection to 12 volts via a fuse and relay during high speed operation and the blower motor resistor is only used for the lower speeds. It sounds like you have a poor electrical connection in the harness or connector or a failing motor. Check the red wire on the connector going to the blower motor. This the high speed wire and should have 12 volts when switch is set to high. If the wire still has 12 volts when the blower quits, then you likely have a failing blower motor or a damaged wire going to the motor that when overheated breaks connection. Chevy blower motors are known to draw excess current as they age and discolored wires are the telltale of over current draw. Inspect the connectors and wires closely for signs of overheating.
 
The blower may be running off a circuit breaker  More on that later.
Chevy uses a HIGH SPEED RELAY to power the fan on HIGH and it too may be failing but I'm inclined to suspect a circuit breaker.

On my Workhorse there is a terminal labeled for the HEATER (HEVAC) blower and it is protected by a fuse. but they did not hook up there. they hooked to AUX-1 which is a breaker.. THankfully the wire is clearly labeled so I was able to figure it out and replace the faulty breaker.
 
touchracing said:
I always remove and visually inspect the resistor first because 99% of the time that's the issue.
Click to expand...
I would agree but on HIGH it is never the issue. it's also "not there" when on HIGh. it is bypassed.

But ... The bypass conneciton is often made AT the resistor

And if. as on mine the circuit breaker is a circuit breaker and not working properly.

Well that is EXACTLY how mine worked till I replaced the breaker.
 
Is it a circuit breaker for only HIGH ?  Because  when it stops if  I move the speed down it immediately runs, if I move it back to HIGH it stops untill after a minute of two then it will  return to operating on HIGH.  So, it could be a bad circuit breaker if it is only used on HIGH.

I know I am getting wordy in explanation! 

But I think I have:
Ruled out the resister (it will run on HIGH even if resister removed.)   
Ruled out the motor (because it will run fine continuously at other speeds)
Ruled out the relay that was close to the resister under the hood (I installed a new relay.  With this relay removed it does not run at any speed)
Ruled out a blown fuse (it resumes operation after a time of rest)
Ruled out bad wiring (it is consistatly the same on how it runs, stops, and resumes)


I think this leaves as a possible cause that I can think of:
A faulty relay that is only used for HIGH that I have not located
A faulty breaker that is resetting

Now I KNOW I am getting wordy !
 
Bjwinspect said:
Now I KNOW I am getting wordy !
Click to expand...

No your Good....Your giving information and it's easy to read.

Now if it was one long paragraph....ALL IN CAPS. Then we might have a problem. ;D ;D
 
Bjwinspect said:
 
Ruled out the motor (because it will run fine continuously at other speeds)
Click to expand...

You can rule out the motor if it was replaced and the problem still occurs, until then, it's still a potential cause. The high speed winding on the motor may be drawing too much current causing a thermal overload or fault at a connector and that connector may be inside the motor housing. Locate the high speed wire where the motor is connected. Use a volt meter or a test light to monitor the wire and turn the fan on high and wait till it stops. If your test light or meter still shows 12v but the motor has stopped then it's the motor because the circuit (relay, fuse, switches, etc) has not interrupted power to the motor. If you lose the 12v when the motor stops, power is being interrupted and now the fun starts.
 
Well it might be the switch. but I'd not expect that.  NO the breaker is for all speeds and you more or less just ruled it out too. at this point all I can suggest is take a test light to the path of power and see where it is bright and dark. 
 
Update: The motor only has one power feed.  It goes dead when the fan stops.  So maybe the switch..  I guess if I wanted to eliminate a medium speed, I could try bypassing that speed at the resister..  I have not yet tried to get to the wiring at the back of the switch.  It?s really not that big of a deal..just trying to figure it out
 
I know your said you replaced it but older GM vehicles that the high blower quits is usually a high blower relay. Very common and easy to replace. Sometimes the plug at the relay gets so hot that it melts the inside of the plug and causes a bad connection.
 
Update:  I found a 30 Amp circuit breaker in the fuse panel under the dash that was getting hot and opening the circuit.  The AC, and lower speeds all work without this breaker.  I find it hard to believe that just a fan would need 30 amp, but I have not found anything else on the circuit.  This problem has lasted a year and 11,000 miles, it has always done fine on lower speeds.  I will replace the breaker and see if that fixes.  It may be a few days before I can tinker with it again.
 
Update:  the new circuit breaker also tripped when on high.  I removed the fan, it seems to run normally.  It seems like it will continue to run without tripping the breaker when not installed, it?s not rubbing on anything when it is installed.  I believe that the resistance of the air being blown at high is what is putting a strain on it causing overheating and tripping the breaker.    It actually looked real clean, but I?m going to clean it up some more and reinstall.    I have not located a cabin air filter.. air flow does not appear to be restricted coming out of the vents
 
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