1999 Tahoe Blower (high speed only) Stopped Working

[rage]

I have a 1999 Tahoe. The high speed (only) stopped working. I replaced the blower switch and the blower relay. I checked the voltages and continuity between the various components and all seem ok though I do not have a wiring diagram to be sure. The voltage (purple wire) to the blower increases as the speed selecter is switched from low to high while connected to the blower except at max blower speed the voltage at the blower is zero. However when this same wire is disconnected from the blower the voltage to ground is ~12 volts at all four blower switch speed positions including max speed. There is no evidence of any over heating or corrosion of any connections or wires. I have detailed voltages at all of the various components/terminals versus the four blower switch positions if that is useful.
Since the blower runs fine at all but the max speed I am assuming it is not the pproblem. I only see two wires to the blower 1.) the purple power wire and 2.) the black ground wire. I am at a loss as to what is wrong. Any help is appreciated.

Thanks

 

[bowtiefreak]

resistor?

 

[ezdaar]

91-99 all have the same problems.
Its either the switch or the spring resistor thing thats mounted under hood in the heater core box.

Start by jumpin the socket that switch plugs into.. if blower goes to high, then its switch, if it doesn't its the resistor thing under hood...
If switch, buy new one. if resistor, go hit junk yard.
Had same problem on a 91, 94 and 96 S-10 and a 96 camero..

 

[SunlitComet]

What resistor under the hood?

the high activates a relay that bypasses the resistor. If you have replace the switch and the blower high speed relay as stated then look for a blown blower fuse in under-hood box should be a 50 Amp ****-type. In high speed the fan switch activates a relay to bypass the in cab fuse for blower power and draws power from the under-hood box fuse instead. Since you said you have 12v at blower wire even in high the above seems unlikely and maybe the blower motor commutator is really fracked but check it anyway. Physically remove and check the fuse in case there is corrosion on it.

 

[bowtiefreak]

https://www.napaonline.com/Catalog/...R76_0239905477&An=599001+101997+50014+2014365

 

[SunlitComet]

Good call. I still keep referring to it as not being under the hood since it is part of the box inside the cab. kinda sorta.:-/

---------- Post added at 04:07 PM ---------- Previous post was at 04:04 PM ----------

Keep thinking it is near the blower relay. Oops.

 

[rage]

What resistor under the hood?

the high activates a relay that bypasses the resistor. If you have replace the switch and the blower high speed relay as stated then look for a blown blower fuse in under-hood box should be a 50 Amp ****-type. In high speed the fan switch activates a relay to bypass the in cab fuse for blower power and draws power from the under-hood box fuse instead. Since you said you have 12v at blower wire even in high the above seems unlikely and maybe the blower motor commutator is really fracked but check it anyway. Physically remove and check the fuse in case there is corrosion on it.

I checked the 50 amp fuse and ok & no corrosion.

At blower switch positions of 'low' , 2, 3 and 'HI' there is 12 volts at the blower power wire connector with the connector NOT attached to the blower. With the blower power wire connector connected to the blower there is ~3 volts at the 'Low' switch position, ~6 volts at the '2' switch position, ~8 volts at the '3' switch position but 0 volts at the 'HI' switch position. This makes sense for blower switch positions of 'low' , 2, 3. The 12 volts for the 'HI' blower switch position with the blower power wire connector NOT attached to the blower but 0 volts when the blower power wire connector IS attached to the blower I am having trouble understanding.

PS Sorry for the multiple posts on this subject. My thought was that I did not want to miss the person with the answer by posting where that person did not see it. Lesson learned.

 

[SunlitComet]

If you replaced that relay how about some loose wire terminal or something may be that wire connection is breaking when being flexed?

 

[rage]

I found it. It was the single inline red wire connector located under the dash between the 50 amp fuse feed and the relay. It was melted internally and would pass 12 volts with no load but 0 volts under load.

Thanks all.

 

[SunlitComet]

When you replace it with an equivelant sized wire may knock the fuse down to a 40 amp or to get an extra safety factor in there. The fan amp load is about 23-27 amps. So you should be fine.