air and heat blower will not run

[linda horton]

1998 500SL is there a way to test the blower relay to see if it is the problem. All fuses are ok. The relay has four wires . If we ground the blue wire ,on the relayto the black wire, on the relay the blower will come on. If I put a meter on yellow wire, and turn the speed control of the fan and turn it up to hight .It read 6 volts. the red wire reads 12 volts, the black is a ground.
The fan will not come on any setting (air, hear ect) does this sound like a bad relay switch or something else. thanks Linda

[stevebfl]

Sounds like a blower regulator.

[linda horton]

Stevebfl thanks for replay. do you know of any why to run a test on the relay switch Linda

[stevebfl]

Which relay switch are you talking about?

The blower is controller by a device called a blower regulator. It works like a huge transistor. The in and out (of the transistor) make the blower connection to ground, based upon the transistor base input signal strength which is a 0-6v signal coming from the pushbutton contoller.

Your description of testing sounds like your are on the wiring to the regulator (without a drawing I don't remember wiring colors).

On 129's I have tested the wiring was at the rear of the fuse box in a single conector.