Are you talking about the blower control switch? I'm not sure where that is. Is it attached to the controls in the dash?

I haven't done any voltage testing on that. How and what am I looking for?

 

I'm not sure on the blazers. On my full size GMC pick up the control switch on the front panel had different wires for each position for fan speed. Bad thing is that I had to replace all the controls because that is the only way they are sold. Maybe someone who has replace thiers can give more info.

 

Auto Zone has this part which I have attached an image of. Anyone know where it is located? Is this connected to the controls in the dash?

 

Hoping for some new ideas.

I just replaced the control switch in the dash and still no blowing. In total I have replaced the switch, relay, and resistor. I've also checked the fan and it works fine when I jump it directly to the battery. I don't think I have anything else left to change out.

Anyone got any new ideas. Its hot here in California. Need to get this puppy blowing some cold air.

 

In the instrument panel fuse block, fuse #6, HTR A/C, 20 amp fuse must show battery voltage on both terminals with the ignition in the START and RUN positions. Do not remove the fuse when testing it.




Disconnect the blower relay. In the relay socket there are 5 wires. Here's how to test them:

The red wire must show battery voltage at all times.

The black wire must show less than 5 ohms resistance to ground at all times.

With the ignition in the RUN position, the mode switch set on HEATER, and the blower switch set on HIGH speed, The orange wire must show battery voltage.

With the ignition in the RUN position, the mode switch set on HEATER, the dark blue wire should show a different voltage, (less than battery voltage) on each of the blower speeds 1, 2, and 3.

Purple: Goes from the relay socket to the blower motor. If you apply battery voltage to the terminal in the socket, the blower must run on high speed.

Post your results.

 

Picked up a new multimeter.

Red wire at relay connection shows battery voltage.

Orange with switch set to high and heat shows battery voltage.

Connected the black to the relay connector and the black wire on the fan connection and got less that 5ohms.

Orange didn't show a difference in voltage it was staying at 12 volts in all fan speeds.

Testing across the fuse is difficult. They are the smaller style fuses and have a pin hole connection. With the fuse out I get 12 volts across the connection. At the fuse the best I could get it to show was 6volts but I think this may have been because I couldn't get a good connection at the terminals. I did swap the fuse with another fuse that was working and no change.

Jumped battery to the purple and black wires on the relay connector and the fan turned on high.

Fan still isn't blowing with everything back together.

 

Just tested the orange wire again since it was acting odd the first time.

This time I get battery voltage at high on the switch but no power on 1-3 speeds.

 

Ignition in the RUN position, and the multimeter set on DC volts, black probe to a good clean ground. Without removing the 20 amp fuse, touch the red probe to each of the terminals on the 20 amp fuse. Post the results.

EDIT: Remove the relay from its socket. In the socket, jumper the red wire to the purple wire. Does the fan work on high speed?

 

Fuse shows battery voltage on both ends of the fuse when connecting to the vehicle ground. I was trying to jump across the fuse previously.

Jumping the red to purple wires in the relay connector does not power the motor.

I was doing some hunting online and some people said it may also be related to ignition switch failure. Thoughts on that?

 

Bingo, There's the problem. The motor has to run on high speed when you jumper those two wires together.

Earlier, I had you test the black wire from the relay socket to ground. Needs to be less than 5 ohms. It is the ground for the relay AND the blower motor.

The test that you performed... "Connected the black to the relay connector and the black wire on the fan connection and got less that 5ohms." This tested the resistance from the relay socket to the blower motor, but NOT to chassis ground.

The problem is the ground wire connection to the body/engine ground is bad. The black wire grounds to the rear of the left cylinder head, not a fun one to get to. The easiest way to repair it is to splice a piece of 12 ga wire on to the black wire at the blower motor, solder would be best. Don't cut the black wire, splice the new piece to it. Attach the other end to a good body ground or to the engine block.

The other test you did... "Jumped battery to the purple and black wires on the relay connector and the fan turned on high." This supplied voltage and ground to the motor and it ran at high speed. You actually bypassed the bad ground.


Gotta do the tests as instructed to get the proper results