High speed on fan Doesn't Work

[Rmhord93561]

1997 Chevy Tahoe 4x4 ls
All the blower speeds work except high. Checked all fuses,, good. Checked and tested relay by blower resistor. Good. Replaced resistor, blower and Control unit in dash. Still no high speed. What am I missing? High should be a direct 12v to blower. Only lower speeds go through resistor. And they all work . No high speed, like turning fan off.

 

[DieselTech]

1997 Chevy Tahoe 4x4 ls
All the blower speeds work except high. Checked all fuses,, good. Checked and tested relay by blower resistor. Good. Replaced resistor, blower and Control unit in dash. Still no high speed. What am I missing? High should be a direct 12v to blower. Only lower speeds go through resistor. And they all work . No high speed, like turning fan off.

So you checked both fuses & the blower motor relay behind the glove box.

1 fuse is in side of dash.
1 50 amp or so maxi-fuse under the hood.
Then the relay behind the glove box.

 

[scott2093]

Replaced resistor, blower and Control unit in dash. Still no high speed.

I had to go through a couple of feepay control units to get one that didn't have the exact issue yours is having....which stunk because they were pristine looking..... but mine is a 93
I don't recall all the details at the moment

 

[CrustyJunker]

When you had it apart, were the connectors in good condition at the controls? The lower speeds can overheat the fan connector and melted plastic gets on the contacts - which prevents the relay from turning on.

If the relay gives you an audible click, make sure you have 12V actually coming out of the relay, too. A poorly made parts store replacement roasted on me once. Heard the click and the coil pulled in, but the tips inside were fried.

Good luck, and let us know how it goes!