Caveman357

The fan only works when its warm out. But when its cold out it will not work. (no defrost=no see) I have checked all fuses and was looking for a relay in the system, but no luck. Took it to a dealer for another problem and had them check this while it was in. They had no clue. It would not work on the lot, but would work in the garage. Been searching for some time now and found this for a 99.
Sounds like a resistor on this one. GM uses them. You can test the blower motor by disconnecting it and jumping 12v direct from your battery. That will confirm the blower is working. The resistor controls all the speeds. The part should not be expensive and is usually located under the hood on or around the evaporator box.
Does anyone have a clue?

MDTAHOE

It should be in the box near the blower motor. Although I am not completely sure because I do not think I have done one on these trucks yet.However that is where it is located in 99%. The part should be less than $30.00

shawnvw

Depends if you have automatic climate controls or not. If you do, you have whats called a blower motor control processor. It acts like a resistor, but changes the fan speed based on a variable 5v reference from the blower motor controls.
If not, you just have a resistor....both are underneath the passenger side of the dash near the blow motor.

You really need to check the blower motor itself with a jumper to the battery. The brushes could be bad in the motor causing it to act this way. if it works using the jumpers, but not when plugged in, you need to test for voltages at other locations(depending on what system you have) to find out what the problem is.

73shark

Welcome to the Tahoe forum. I'm thinking since it only works at higher temps, maybe it's bearings in the motor.

Caveman357

It does have automatic climate controls.
I have an appt. at the shop tuesday.
Old school friend works there and seems to think it may be the temp control as well.
Looks like its time to check the bank account again.
I will report back as to what was wrong.

Caveman357

Well just got the news.
Blower motor is the problem.
It has a tight bearing, which allows it to work in warm temp. but would seize in cold temps.
Of course there is more bad news.
Rear brakes are wore out.
Going to have the steering wheel arm replaced too.
Would do it myself, but snow and a packed garage, plus no time.
Just a tad over a grand.
Not to bad, got it for 8 grand under book value.
Should be done Wed. evening, we will see.

Caveman357

Update:
Wrong. Back in the shop with the same problem.
Will update again shortly.