Changed all electrical components and still no heat. 99 xj classic

[7roy1117]

I have searched through forum after forum and there is no answer in any of them to the problem I’m having. Last year the blower motor stopped coming on completely. Right before that it was in and out at random. I’ve replaced the control switches, blower motor, resistor, relay, and fuse. When I check the power coming out of the blower motor pigtail it is pulling a constant 12v. When I run my blower motor directly to the battery it comes on. When I connect the pigtail to the motor it does nothing. I can hear the blend door moving when I change the direction of air. But no air will come out. Is there a vacuum system that helps run the blower motor itself? If so what are the components called that could be suspect? I’ve been scratching my head with this for quite a while now. Any help or info is appreciated.

 

[Unclewolverine]

Sounds like a bad ground to me. I'd splice the ground wire directly to the battery.

 

[7roy1117]

Sounds like a bad ground to me. I'd splice the ground wire directly to the battery.

Would you splice in and eliminate the original plug ground or tie the direct ground to both?

 

[7roy1117]

Sounds like a bad ground to me. I'd splice the ground wire directly to the battery.

I did this when I got home and no luck at all. Still dead. Still pulling a constant 12v at the blower motor plug, fuse, and relay.

 

[Saudade]

Well, it looks like the the blower gets power directly from the relay, then grounds through the resistor. If you have power at the blower, check for power at the resistor. Looks like the BK/TN (Pin 7) is the bypass so should show full volts. The others step down based on the switch settings to provide slower speeds.