My 2003 Blazer 2 door with 4WD and 82K miles has good AC/Heater fan from speeds 1-3 but no. 4 has no fan at all. if it was reversed: no 1-3 and 4 (high) is good, it would be the resistor board is bad. High is the only fan speed not controlled by a resistor. But why no fan in 4 speed? A/C works fine. Also the far left air vent is not working. The two center vents are blowing cold air.

 

At the blower motor relay, (center of firewall under the hood), there are 2 orange wires: One must have battery voltage at all times. The other orange wire must have battery voltage with the ignition in the RUN position, the mode switch in any position except OFF, and the blower switch on HIGH. Post your results.

 

At the blower motor relay, Orange no. 1 had batt. at all times. The Orange no. 2 was Zero with ign. off and 11.8VDC with 'ignition on' and fan switch on High. My battery voltage is about 12.69 VDC. I would have had this earlier, but had to watch the end of the 24 Heures du Mans. Yellow Corvette was fourth in class.

 

Unplug the relay, if the black wire shows more than 5 ohms resistance to ground, repair the open circuit to ground in the black wire. If the black wire shows less than 5 ohms resistance to ground, replace the relay.

 

Looking at the square connector , I have a Brown wire that shows 'Zero' Ohms resistance. There is a Black wire , but it is open. If the Brown wire is the Ground, it would mean it is the relay. Where do I find a Blower motor relay. Is it a dealer only item or can I find it at NAPA, AZ,or AAP? Could the brown wire be the Ground? If it is a bad ground, why doesn't it affect the 1,2,3 speeds on the blower?

 

Diagram of connector block.
**************************
o Orange Orange o

o Blue/green >>>> Clip for connector

o Black Brown o
****************************
Note: Brown = Zero Ohms, Black = Open

 

The black wire is the ground for the relay coil. The small orange wire is the trigger wire for the relay coil. If the small orange wire has voltage when the blower switch is in the HIGH position, it means the dash switch is capable of triggering the relay. If the black wire is open to ground, the relay will not latch and the high speed blower will not operate. Splice on a wire to the black wire and connect it to a good ground.

 

Got it,Captain Hook. Thanks!

 

It works now? Or you understand how to repair it?

 

No, it still doesn't work, but only because I haven't repaired it yet. I can't find the 'crimp' splice to add the grd to the black wire. Also I don't have a soldering iron to solder one on. I will try to get a crimp slice today. Oh, yes, on Monday , I tried to use the DVOM cable to create a temporary grd wire, but that didn't work. My Haynes manual has some diagrams, but apparently the HVAC blower motor wasn't on their list of critical components. Good news is their is a great grounding strap on the firewall just behind the blower relay.