Heater not blowing, help

[shorod]

If the motor has a thermal-related issue that causes it to go open after it's been running and heats up, it should not cause a relay to fail.

In what way was the relay bad? Was the coil open, or were the contacts stuck open or closed?

If the contacts were "welded," that would imply either a defective relay or a severe current draw at turn-on. If the blower fan is typically left on high speed when the car is started, those relay contacts are seeing a huge current surge when it closes. That can cause arcing, which leads to carbon tracing, reduced conductivity, and usually eventual "welding" of the contacts.

If the coil is open, then there may be a reverse emf diode that is faulty (not too likely) or the relay may have been faulty. An open coil would not be caused by a faulty blower motor. Rather, the coil probably failed due to poor assembly -- vibration failure due to a poorly prepared magnet wire, cold solder joint, or too long or too short coil wire lead to terminal.

-Rod

[jrngmn]

I swapped out the relay on a whim because it was $7. When I pulled it out the contacts were discolored and looked electrically shorted (burnt). When the fan worked after installing the new relay, I figured problem solved. Then it stopped again and I'm assuming the same thing is going on. I won't have time to mess with it until Tuesday, but I will try the suggestions. thanks.

[shorod]

You should attempt to determine the cause of the discoloration on the old relay contacts. Are you referring to the contacts external to the relay, or did you open the relay and physically inspect the "guts?"

If you are referring to the external contacts, you need to determine the cause of the discoloration. If the discoloration is actually due to arcing, you probably have a loose connection that should be remedied before it melts the relay connector or starts a fire.

If the relay had silver plated contacts, the discoloration may be due to oxidation, which is actually a better conductor than silver itself (silver oxide is actually one of the best conductors available).

-Rod

[jrngmn]

Originally Posted by shorod

You should attempt to determine the cause of the discoloration on the old relay contacts. Are you referring to the contacts external to the relay, or did you open the relay and physically inspect the "guts?"

If you are referring to the external contacts, you need to determine the cause of the discoloration. If the discoloration is actually due to arcing, you probably have a loose connection that should be remedied before it melts the relay connector or starts a fire.

If the relay had silver plated contacts, the discoloration may be due to oxidation, which is actually a better conductor than silver itself (silver oxide is actually one of the best conductors available).

-Rod

I'll exercise due diligence in the discoloration as it was the outside contacts. I think you were on the right path with the blower motor because it was working again today when I did a spot check after work. I'm thinking like you said it's going open after warming up. The resistor block seems to be working because I can change blower speeds without incident. Is the Autozone $40 blower good enough or do I spend the $108 at the dealer?

[shorod]

The Autozone blower is probably good enough, but be aware that it may be a more "universal" style and MAY require you to solder wires and/or re-engineer the vent (if equipped).

If you opt to replace the blower motor, you may want to remove the old and make sure you can get the squirrel cage fan off without it breaking before going on your parts run.

-Rod